Fatty liver reexamined choline and mitochondrial toxin amelioration

Abstract

Choline supports phospholipid synthesis, membrane integrity, neurotransmission, verylowdensity lipoprotein export, and one-carbon/epigenetic pathways, yet most United States adults fall short of adequate intake. Fatty liver is now viewed as a mitochondrial-centric metabolic–inflammatory disorder; ethanol and excess linoleic acid (LA) can magnify bioenergetic stress when choline is insufficient to sustain phosphatidylcholine/phosphatidylethanolamine. This narrative review examines whether optimized choline delivery, alongside reduced exposure to mitochondrial toxicants, offers a rational therapeutic approach. Low choline intake associates with higher liver fat and aminotransferases. In rodents, choline deficiency combined with ethanol or LA lowers mitochondrial membrane potential, limits β-oxidation, and promotes steatosis and inflammation. Advanced formulations-especially citicoline-demonstrate favorable absorption and tissue choline delivery and may lessen trimethylamine-N-oxide formation versus free choline salts. Early, small human studies suggest that choline repletion, together with curtailed ethanol or dietary LA, can reduce intrahepatic triglyceride content and improve insulin sensitivity, though large randomized trials are lacking. Framing fatty liver as nutrition-modifiable mitochondrial toxicosis highlights correctable choline insufficiency when the liver is burdened by ethanol or excess LA. A dual strategy—using higher-bioavailability, gutmicrobial trimethylamineNoxide-sparing choline forms and mitigating mitochondrial toxicants-targets core bioenergetic defects, may reverse early steatosis, and warrants testing in adequately powered clinical trials.

Key Words: Choline; Citicoline; Fatty liver disease; Linoleic acid; Mitochondrial dysfunction; Phosphatidylcholine; Phosphatidylethanolamine; Phospholipid metabolism; Dietary intervention; Hepatic steatosis

Core Tip: This review recasts fatty liver disease as a reversible mitochondrial toxicosis driven by linoleic acid (LA) and ethanol when choline intake is inadequate. It collates pre-clinical and pilot clinical evidence showing that bioavailable, gutmicrobial trimethylamineNoxide-sparing choline carriers (citicoline, αglycerophosphocholine), together with LA restriction or alcohol abstinence, restore phosphatidylcholine/phosphatidylethanolamine balance, revive hepatic respiration and shrink intrahepatic fat. This dual nutrition-first approach targets the root bioenergetic defect, offering a low-risk route to halt steatosis progression and warrants large, randomized trials.

INTRODUCTION

Nonalcoholic and metabolicdysfunction–associated fatty liver disease (NAFLD/MASLD) has exploded into the most common chronic liver disorder worldwide, now affecting roughly onethird of adults and trending higher each year[1]. Parallel to this epidemiologic surge, United States surveillance data show that the vast majority of Americans-well over 80% in every National Health and Nutrition Examination Surveys (NHANES) cycle from 20032018-still fail to meet the adequate intake (AI) for the methyldonor nutrient choline[2]. These two trends are not coincidental: Emerging mechanistic work positions choline insufficiency at the center of a toxindriven collapse of hepatic mitochondrial function that culminates in steatosis, inflammation, and progressive fibrosis.

Mitochondria sit at the nexus of this pathobiology. Contemporary reviews detail how impaired βoxidation, defective respiratorychain flux, and excessive reactive oxygen species (ROS) production form an early, actionable lesion in NAFLD/MASLD[3]. Key exogenous stressors amplify that lesion: Dietary linoleic acid (LA), which peroxidizes into 4-hydroxynonenal (4-HNE) and other aldehydes that punch holes in the inner mitochondrial membrane[4], and ethanolderived acetaldehyde, which directly inhibits the pyruvatedehydrogenase complex and throttles oxidative phosphorylation[5]. Decades of lipidbiology research also warn that modern Western menus deliver LA at 6%-10% of total energy—far above historical norms and far outpacing protective omega3 intake[6].

When scarce choline collides with these mitochondrial toxins, hepatic phosphatidylcholine (PC) and phosphatidylethanolamine (PE) pools shrink, verylowdensity lipoprotein (VLDL) export stalls, and triglycerides clog hepatocytes. Classic depletion–repletion studies in humans demonstrated that frank choline deficiency alone can trigger steatosis within weeks—a lesion rapidly reversed by intravenous choline[7]. More recently, experimental nonalcoholic steatohepatitis (NASH) models show that citicoline [cytidine diphosphate (CDP)choline] rescues mitochondrial redox signaling and attenuates steatoinflammation even in the face of a highLA load[8].

Not all choline vectors are created equal, however. Populationscale data associate chronic use of αglycerophosphocholine (αGPC) with a 46% higher 10-year stroke risk-an effect plausibly mediated by gutmicrobial trimethylamine-Noxide (TMAO)[9]. In contrast, citicoline boasts about 95% oral bioavailability, negligible TMAO formation, and a robust neurologic safety record, making it an attractive therapeutic backbone[10]. Mitochondriacentric drugdevelopment pipelines likewise converge on phospholipid restoration and toxin attenuation as highyield targets for reversing hepatic bioenergetic failure[11].

THE PIVOTAL ROLE OF CHOLINE IN HUMAN PHYSIOLOGY

Choline was formally acknowledged as an indispensable nutrient by the Institute of Medicine (IOM) in 1998, and occupies a pivotal position in human physiology due to its multifaceted contributions to vital biochemical processes[12]. This quaternary ammonium compound is integral to the primary composition of cell-membranes, neurotransmitter synthesis, lipid transport, and methyl-group metabolism[13,14] Its recognition as an essential nutrient underscores its non-redundant roles, which have been elucidated through decades of scientific inquiry and are increasingly appreciated in contemporary medical research for their implications in health and disease.

Dietary choline traverses the intestinal lumen where its absorption is facilitated by specialized transporters[15]. Choline’s metabolic fate primarily involves its conversion to phospholipids like PC through the CDP-choline pathway, a process ubiquitous across all nucleated cells, though it is particularly prominent in hepatocytes due to their high capacity for phospholipid synthesis[16]. Figure 1 shows how choline is converted to PC, a major structural lipid in cell membranes, through a series of biochemical steps including phosphorylation and CDP-choline intermediate formation.

Figure 1 Choline’s conversion to phosphatidylcholine. This figure illustrates the cytidine diphosphate (CDP)-choline pathway, a critical metabolic route converting choline into phosphatidylcholine (PC), the predominant phospholipid constituting over 50% of mammalian cell membranes. Choline is initially phosphorylated by choline kinase to form phosphocholine, which cytidine triphosphate: Phosphocholine cytidylyltransferase then transforms into CDP-choline; subsequently, CDP-choline: 1,2-diacylglycerol cholinephosphotransferase catalyzes its conversion into PC. The diagram highlights PC’s amphipathic structure—featuring a hydrophilic head and hydrophobic tails—essential for membrane fluidity and signal transduction. In hepatocytes, where this pathway is notably active, PC facilitates very-low-density lipoprotein assembly, exporting triglycerides to prevent lipid accumulation. CDP: Cytidine diphosphate; PC: Phosphatidylcholine.

Moreover, choline’s metabolic versatility is exemplified by its rapid intracellular transformation. Upon cellular ingress, choline is phosphorylated to PC via choline kinase, a pivotal step in PC biosynthesis[17]. Betaine, a trimethylated derivative, plays a crucial role in methyl group metabolism by donating methyl units to homocysteine (Hcy), thereby facilitating its conversion to methionine (Met)-an essential amino acid integral to proteinogenesis and S-adenosylmethionine (SAM) synthesis[18]. In the sections that follow, we will analyze the implications of these processes, exploring how choline’s contributions to membrane dynamics, neurotransmission, and methyl-group metabolism inform our understanding of health maintenance, disease etiology, and the potential for targeted therapeutic interventions.

PHOSPHOLIPIDS ARE ESSENTIAL FOR CELLULAR STRUCTURE AND MEMBRANE DYNAMICS

Choline is essential for the biosynthesis of PC, the dominant phospholipid in mammalian cell membranes and subcellular organelles. PC makes up about 50% of total membrane phospholipids and accounts for roughly 95% of the total choline stored in tissue[19-21]. PC is essential for preserving membrane integrity and fluidity, properties that are indispensable for cellular function, particularly in tissues characterized by rapid cellular turnover, such as the liver and the developing brain. Furthermore, choline contributes to the synthesis of sphingomyelin, a key constituent of myelin sheaths and a mediator of cell signaling cascades[22]. Inadequate choline availability impairs the capacity of cells to construct or repair their membranes, a deficit that compromises tissue homeostasis and function[12].

Given the vital role of choline and PC in maintaining membrane integrity in tissues like the liver, it is essential to examine how these compounds support the function of hepatocytes, which are integral to lipid metabolism, orchestrating processes such as lipid synthesis, modification, and export. These cells exhibit exceptionally high metabolic activity, processing lipids at rates that can exceed 100 g per day in humans, which imposes substantial demands on their structural integrity[23]. To withstand the rigors of continuous lipid flux across their membranes, hepatocytes require a resilient architecture, conferred by phospholipids to fortify the membrane against the mechanical and biochemical stresses of perpetual lipid processing while facilitating the efficient transport of lipids out of the liver. Beyond its structural and neurological roles, choline is integral to hepatic lipid metabolism and systemic metabolic equilibrium[24]. In the liver, choline is incorporated into phospholipids, which form the backbone VLDLs essential for triglyceride export. A deficiency in choline disrupts VLDL assembly, resulting in triglyceride accumulation within hepatocytes—a hallmark of hepatic steatosis.

PE, another key phospholipid constituting 20%–30% of cellular membranes, also plays a substantive role in membrane dynamics and bioenergetics. The ratio of PC to PE governs key biophysical properties of cellular and organelle membranes, including as fluidity, curvature, and bilayer asymmetry. PC, characterized by its bulky choline head group, stabilizes the bilayer structure, whereas PE, possessing a smaller ethanolamine head group, promotes negative curvature, facilitating processes like vesicle formation and exocytosis[25]. This compositional balance, historically studied for its role in cellular dysfunction such as Alzheimer’s disease, where the PC to PE ratio can decrease by up to 20%[26], also sustains membrane asymmetry essential for signaling, such as during apoptosis[27]. Furthermore, the PC to PE ratio influences lipid metabolism, as these phospholipids interconvert via biosynthetic pathways, yielding signaling molecules such as diacylglycerol (DAG). In addition, organelle-specific differences, such as elevated PE levels in mitochondrial membranes supporting adenosine triphosphate (ATP) synthesis, highlight its functional significance[28]. Thus, this ratio is pivotal to membrane dynamics and cellular homeostasis.

Elevating PE levels, either through supplementation with its precursor ethanolamine, significantly extends lifespan across various organisms, including yeast, flies, and mammals[29]. On the other hand, reducing PE levels results in an increased production of ROS. Furthermore, PE is indispensable for mitochondrial function, where it supports the electron transport chain (ETC) and maintains mitochondrial membrane integrity[30]. Consequently, modulating PE levels emerges as a promising strategy to extend lifespan by simultaneously enhancing autophagy, mitigating oxidative stress, and supporting mitochondrial function. Targeting PE metabolism could pave the way for novel therapeutic interventions aimed at combating age-related diseases and promoting healthy aging[31].

While PC remains the predominant phospholipid in cellular membranes, an exclusive emphasis on PC optimization has overlooked the important contributions of PE to cellular homeostasis and metabolic function. An imbalance favoring PC could perturb this metabolic equilibrium, potentially leading to the depletion of PE, which is particularly abundant in mitochondrial membranes and crucial for ATP synthesis. Historically, phospholipid research has prioritized PC due to its prevalence; however, contemporary investigations underscore that optimizing both PC and PE is essential for comprehensive metabolic performance.

CHOLINE’S MULTIFACETED ROLES IN CELLULAR FUNCTION AND METABOLISM

While phospholipids are fundamental to cellular structure and membrane dynamics, choline-the key component of PC-extends its influence far beyond membrane integrity. Choline is indispensable for several critical biological processes, including lipid metabolism in the liver, neurotransmission in the brain, and methyl group metabolism for epigenetic regulation. The following sections explore these multifaceted roles, underscoring choline’s central importance in maintaining cellular function and metabolic homeostasis.

NEUROTRANSMISSION AND COGNITIVE FUNCTION

Choline’s significance extends into the realm of neurotransmission as the precursor to acetylcholine (ACh), a neurotransmitter pivotal to both central and peripheral nervous systems. ACh facilitates memory consolidation within the hippocampus and governs neuromuscular signaling for muscle contraction[32]. The availability of choline in neuronal terminals represents a rate-limiting step in ACh synthesis; when choline levels diminish, nerve terminals falter in sustaining ACh release, leading to impairments in cognitive performance and motor coordination. This neurochemical dependency has fueled research into choline’s therapeutic potential in neurodegenerative disorders.

FETAL AND INFANT DEVELOPMENT

Choline is essential during fetal and infant development, playing a key role in brain formation and cognitive function. Adequate maternal choline intake supports the development of the hippocampus and other brain regions, enhancing memory and cognitive performance in offspring. Studies suggest that higher choline levels during pregnancy are associated with improved learning outcomes in children[33]. During embryogenesis, methylation reactions are crucial for normal development and long-term epigenetic programming. Choline deficiency shifts the burden to folate and vitamin B12 for methyl group provision; conversely, suboptimal folate intake heightens reliance on choline-derived betaine[34]. Elevated Hcy levels, a marker of disrupted one-carbon metabolism, link choline inadequacy to cardiovascular and neurological risks[35]. Notably, pregnant women with concurrent low choline and folate intake face an elevated risk of neural tube defects in offspring, likely due to compromised methylation during neural tube closure[36,37]. Table 1 presents the AI levels for choline across key demographic groups, as defined by the IOM in 1998. It highlights age- and sex-specific requirements, the heightened needs during pregnancy and lactation, and the widespread shortfalls identified in national dietary surveys.

Table 1 Choline requirements across different populations⁶.

Population group	Adequate intake	Special considerations
Adult men (19–50+ years)	550 mg/day	Increased risk of deficiency with MTHFR/PEMT polymorphisms1
Adult women (19–50+ years)	425 mg/day	Needs may increase with low dietary intake or genetic variants1
Pregnant women (all ages)	450 mg/day	Elevated demand for fetal development; polymorphisms may increase requirement2
Lactating women (all ages)	550 mg/day	Supports infant development through breast milk; higher need sustained3
Infants (0-12 months)	125-150 mg/day	Rapid brain development; adequate intake based on observed intakes in healthy breastfed infants4
Children (4-8 years)	250 mg/day	Supports growth and cognitive development
Elderly adults (51+ years)	425-550 mg/day	Same as general adult needs; absorption/utilization may be less efficient with aging5

¹PEMT and MTHFR gene variants can impair endogenous choline synthesis, increasing dietary requirements.

²Choline supports fetal brain development, methylation, and placental function during pregnancy.

³Choline output via breast milk increases maternal demand during lactation.

⁴Adequate intake for infants is derived from average choline concentrations in human milk.

⁵Aging may impact choline metabolism and absorption efficiency, requiring consistent intake.

⁶This table delineates the adequate intake levels for choline, as established by the Institute of Medicine in 1998, across distinct demographic groups. Adult men require 550 mg/day, a threshold reflecting their vulnerability to hepatic steatosis, particularly in those with PEMT polymorphisms. Adult women need 425 mg/day, though over 90% fall short per National Health and Nutrition Examination Surveys, while pregnant and lactating women demand 450 mg/day and 550 mg/day, respectively, to support fetal synaptogenesis and milk composition. Infants (125–150 mg/day) and children (250 mg/day) rely on choline for myelination, whereas the elderly (425–550 mg/day) face reduced absorption efficiency. These data, grounded in decades of nutritional research, highlight choline’s varying physiological demands across the lifespan.

METHYL GROUP METABOLISM AND EPIGENETIC REGULATION

Choline’s influence further permeates methyl group metabolism and epigenetic regulation, mediated through its oxidation to betaine primarily in hepatic tissues. Betaine serves as a methyl donor in the remethylation of Hcy to Met within the folate-dependent one-carbon cycle, a process integral to DNA and histone methylation and, consequently, gene expression[38]. Betaine and choline also collaborate in supporting liver function, particularly in lipid metabolism and detoxification processes[39]. Betaine then acts as a methyl donor in the Met cycle, converting Hcy to Met[40]. This process replenishes SAM, a crucial cofactor for methylation reactions that facilitate the synthesis of PC and the detoxification of harmful compounds.

GALLBLADDER FUNCTION

Choline also plays a pivotal role in optimizing gallbladder function, primarily through its contribution to bile composition within the hepatobiliary system. As a precursor to PC that constitutes approximately 10%-15% of bile’s lipid content, choline ensures the solubility of cholesterol in the biliary environment[41]. This solubilization is essential for preventing the precipitation of cholesterol crystals, which can coalesce into gallstones—a condition that disrupts gallbladder function and predisposes individuals to significant digestive morbidity[42]. Historically, the significance of choline in bile homeostasis was revealed through experimental models, wherein choline-deficient diets resulted in altered bile lipid profiles and elevated gallstone formation in rodents[43]. Furthermore, PC enhances the emulsification of dietary lipids, thereby facilitating their hydrolysis and absorption within the intestinal lumen. In this context, adequate choline intake is critical for maintaining bile stability and supporting efficient lipid metabolism[44].

HISTORICAL CONTEXT AND EVOLVING KNOWLEDGE

The recognition of choline as an essential nutrient is embedded in a historical narrative spanning over a century, marked by incremental scientific advancements and transformative shifts in nutritional science. Initially isolated in 1862 by German chemist Adolph Strecker from pig and ox bile-fittingly, as the Greek word for bile is chole, hinting at its etymological roots. By the late 19^th and early 20^th centuries, PC’s presence within lecithin, a phospholipid abundant in egg yolks had been delineated. Yet, during this period, choline’s dietary necessity remained overshadowed, as nutritional science historically prioritized the characterization of vitamins such as thiamine and ascorbic acid[45]. In 1850, Theodore Gobley characterized "lecithine", a term derived from the Greek "lekithos" for egg yolk, thereby laying the groundwork for comprehending phospholipid structures. In the mid-19^th century, Adolph Strecker identified choline as a component of lecithin. Lecithin, which contains PC, was later understood to provide choline when consumed.

By the early 20^th century, lecithin was being studied for its health benefits, particularly after Charles Best’s work in the 1930s showed it could prevent fatty liver in dogs, with choline identified as the active component[45]. Choline chloride's therapeutic potential was recognized in the 1930s after research demonstrated its efficacy in preventing fatty liver in animal models, leading to its exploration for liver conditions such as cirrhosis by the mid-20^th century and inclusion in infant formulas by the 1970s[46]. In contrast, choline bitartrate's therapeutic applications emerged later, gaining traction in the 1970s and 1980s for cognitive and neurological conditions like Alzheimer’s disease. By the 1990s, it was widely used in dietary supplements for cognitive enhancement and liver support[47].

The late 20^th century heralded a resurgence of interest, catalyzed by pivotal discoveries that redefined choline’s status. In the 1970s, Richard Wurtman’s investigations revealed that dietary choline modulated cerebral ACh concentrations, with supplementation elevating levels by approximately 50%, thus igniting therapeutic explorations for neurological conditions such as tardive dyskinesia[48]. The definitive substantiation of choline’s essentiality emerged in the 1990s through Steven Zeisel’s meticulously controlled depletion-repletion trials, wherein human subjects on choline-deficient diets exhibited hepatic dysfunction, evidenced by serum aminotransferase (ALT) elevations surpassing twice the upper reference limit in most male and postmenopausal female participants[49].

In response to this robust human evidence, the United States IOM established AI levels in 1998: 550 mg/day for adult men and 425 mg/day for adult women, with escalated recommendations of 450 mg/day during pregnancy and 550 mg/day during lactation to address heightened physiological needs. These thresholds, designed to avert hepatic damage observed in experimental settings, formalized choline’s integration into dietary guidelines[50]. Subsequently, in 2016, the European Food Safety Authority designated an AI of 400 mg/day for adults, reflecting a slightly divergent yet congruent approach grounded in similar preventive principles[51].

Pregnant women require higher choline intake to support fetal brain development, with evidence indicating that maternal supplementation (e.g., 930 mg/day, double the standard recommendation) enhances offspring cognitive processing speeds[52]. Infants and young children depend on choline for myelination and brain growth, reflected in its abundance in breast milk (7 mg/100 mL) and fortified formulas[53]. The elderly, facing potential declines in endogenous choline synthesis and hepatic function, benefit from dietary choline to preserve cognitive and liver health[54]. Additionally, genetic polymorphisms, such as those in the PEMT gene, which affects about 40% of premenopausal women, or methylenetetrahydrofolate reductase variants that impair folate metabolism, amplify choline requirements, rendering dietary adequacy paramount.

PUBLIC HEALTH IMPLICATIONS AND ONGOING RESEARCH

This formal recognition underscored the imperative for dietary recommendations, particularly as national surveillance, such as the NHANES, disclosed that typical American intakes ranged between 300-400 mg/day, with over 90% of individuals falling short of the AI[55]. The historical progression of choline—from an enigmatic biochemical entity to a keystone of nutritional science—epitomizes the iterative refinement of scientific understanding.

Contemporary investigations have since pivoted toward optimizing intake for enhanced health outcomes, notably in neurodevelopment, where maternal choline consumption exceeding 450 mg/day has been associated with cognitive enhancements in offspring, yielding IQ increments of up to 10 points by age seven[56]. In this context, the ongoing exploration of choline’s broader physiological impacts continues to inform public health strategies, ensuring its integration into nutritional frameworks remains both evidence-based and forward-looking.

Another important aspect of the historical journey is the slow translation of knowledge into public health action. Even after 1998, choline remained relatively “under the radar”. For years, many multivitamin supplements and prenatal vitamins did not include choline at all or included only a token amount (far below the AI), reflecting a lag in policy and industry response[57]. National nutrition surveys also only began to track choline intake in the 2000s.

These kinds of data have spurred increased calls from nutrition experts to raise awareness. By the late 2010s, articles in scientific and public health forums began to warn of a potential “choline crisis” if trends in diet continued[58]. In summary, our understanding of choline has progressed from a biochemical curiosity in the 1800s, to an experimentally confirmed essential nutrient in the late 1900s, to now an area of active investigation and concern in the context of modern diets. The historical context sets the stage for why we must pay attention to choline’s roles and ensure dietary adequacy moving forward.

DIETARY SOURCES OF CHOLINE

Choline must be partially acquired through dietary intake to meet physiological demands, given that de novo synthesis via the hepatic PEMT pathway is insufficient[59]. This nutrient is unevenly distributed across food sources, with animal-derived products generally containing higher concentrations than plant-based alternatives. As a result, individuals following vegetarian or vegan diets face distinct challenges in meeting choline requirements, underscoring the need for a detailed understanding of food sources and their relative contributions.

Table 2 summarizes the choline content of common animal-derived foods, highlighting practical sources based on serving size. Eggs and beef liver emerge as the most concentrated sources, with a single egg providing up to 150 mg and a small serving of liver offering over 350 mg. Muscle meats and fish contribute modest amounts, while dairy supplies only trace levels. Given the significantly higher choline content in animal-derived foods, the following discussion and accompanying table prioritize these sources for meeting daily requirements, though plant-based options like soybeans and cruciferous vegetables may contribute modestly to intake and warrant consideration in vegetarian or vegan dietary planning.

Table 2 Dietary sources of choline (animal-derived sources)².

Food item	Serving size	Choline content (mg)	Notes
Beef liver (high)1	3 oz (85 g)	350–360 mg	Top source; high in vitamin A-daily use not recommended
Egg (large) (high)	1 large	147–150 mg	Top source; mostly in the yolk (about 90%); cost-effective and bioavailable
Beef (muscle meat)	16 oz (454 g)	Approximately 500 mg	High iron; excess may pose oxidative stress and ferroptosis risk
Chicken breast	3 oz (85 g)	Approximately 73 mg	Moderate choline source
Milk (whole)	1 cup (240 mL)	Approximately 38 mg	Readily available; minor contribution
Fish (salmon)	3 oz (85 g)	Approximately 56 mg	Healthy fat source; moderate choline

¹High choline content (≥ 100 mg per serving). Top sources for practical intake.

²Choline content of select animal-derived foods. Values reflect typical serving sizes and estimated ranges of choline content per item. Beef liver, egg are high-choline foods (≥ 100 mg per serving). Beef liver, egg items represent top sources based on practical intake potential. While beef liver ranks highest, its high vitamin A content limits safe daily consumption. Eggs offer a cost-effective, bioavailable option for regular use.

Among animal-derived foods, organ meats stand out as exceptionally rich sources of choline. Approximately 500 g (or roughly 4.65 ounces) of beef liver would be needed to supply 550 mg of choline. However, daily consumption of this quantity of liver could quickly lead to vitamin A toxicity, due to its high retinol content-approximately 10000 µg of retinol activity equivalents (RAE) per serving-which is more than double the adult tolerable upper intake level of 3000 µg RAE/day. Consequently, despite its nutrient density, liver is not advisable as a routine dietary source of choline, a caution grounded in the well-documented risks of hypervitaminosis A historically observed in populations with frequent organ meat intake[60-62].

In contrast, skeletal muscle meats, such as beef, provide a more moderate choline contribution, with 16 ounces (454 g) yielding approximately 500 mg-nearly meeting the daily AI for men. However, this quantity of beef also introduces another nutrient excess concern: Iron overload[63,64]. This condition, which is associated with oxidative stress and metabolic perturbations, including lipid peroxidation and insulin resistance, arises from excessive accumulation of unbound iron in tissues. Furthermore, elevated heme iron levels may exacerbate ferroptosis, an iron-dependent form of programmed cell death characterized by the accumulation of lipid hydroperoxides, which can precipitate cellular damage in organs like the liver and heart. In this context, the interplay between habitual dietary heme iron intake and ferroptotic pathways warrants further investigation to determine its long-term impact on human health[65]. Thus, while both organ and muscle meats offer choline, their respective excesses-vitamin A in liver and iron in beef—necessitate careful consideration within nutritional planning.

THE “EGG CRISIS” AND ITS IMPLICATIONS FOR CHOLINE INTAKE: A NUTRITIONAL CONUNDRUM

Among dietary sources, egg yolks emerge as a highly favorable option for daily consumption, delivering a substantial choline payload in a highly bioavailable form. A single large egg yolk provides approximately 150 mg of choline, predominantly as PC[66]. Among dietary sources of choline, egg yolks remain one of the most concentrated and accessible. However, a convergence of sociocultural, environmental, and economic factors has led to a decline in egg consumption—a trend often referred to as the “Egg Crisis”-with potential consequences for population-level choline sufficiency. Historically, the stigmatization of eggs emerged in the 1970s through 1990s, driven by the cholesterol hypothesis, which postulated that dietary cholesterol directly elevates serum LDL cholesterol, thereby heightening cardiovascular risk[67].

Public health edicts, such as those from the American Heart Association, which recommended capping egg yolk intake at three to four per week, catalyzed a precipitous drop in per capita consumption-from roughly 400 eggs annually in the 1950s to fewer than 250 by the 1990s in the United States[68]. This shift gave rise to a widespread preference for egg-white preparations, particularly among fitness enthusiasts, effectively eliminating the yolk-which contains approximately 90% of an egg’s total choline content-from many diets[69]. Although contemporary research has largely exonerated dietary cholesterol as a primary cardiovascular culprit, favoring saturated fat as the dominant driver, the cultural aversion to egg yolks endures[70,71].

Concurrently, the ascent of plant-based diets, fueled by ethical and ecological imperatives, has further eroded egg consumption[72,73]. The EAT-Lancet Commission’s planetary health diet, advocating a mere 1.5 eggs per week, exemplifies this paradigm, which prioritizes sustainability over traditional intake patterns[74]. Such regimens yield suboptimal choline levels; for instance, vegan diets exhibit mean choline intakes approximately 50% lower than omnivorous counterparts[75]. Economic perturbations exacerbate this trend, with avian influenza outbreaks intermittently decimating poultry flocks and inflating egg prices. In late 2024, egg costs in some regions surged by over 50%, rendering this choline-rich staple less accessible and prompting substitution with choline-poor alternatives[76]. These episodic disruptions underscore the vulnerability of relying predominantly on eggs for choline procurement.

EXPOSITION ON CHOLINE SUPPLEMENTS: MECHANISMS, FORMS, AND IMPLICATIONS

Choline bitartrate, a salt form esterified with tartaric acid, dominates as the most prevalent choline source in nutritional supplements, largely owing to its low production costs and routine inclusion in multivitamins and single-nutrient tablets. Comprising approximately 40% choline by weight, a typical 500 mg tablet of choline bitartrate delivers roughly 200 mg of elemental choline. Its limited intestinal absorption of only 10–20% yields a mere 20–40 mg of systemically available choline per 500 mg dose, rendering choline bitartrate among the least efficacious modalities for nutritional supplementation[77,78]. Moreover, its microbial conversion in the gut to trimethylamine, which hepatic flavin monooxygenases oxidize to TMAO, introduces significant concerns. For example, TMAO levels above 3.5 μmol/L have been correlated with heightened cardiovascular risk, notably endothelial dysfunction[79]. Thus, despite its widespread use driven by affordability, choline bitartrate’s drawbacks prompt recommendations for more bioavailable forms to optimize therapeutic outcomes.

Choline chloride which has historically been prioritized in animal nutrition due to its elevated choline content of approximately 74% by weight, outperforms choline bitartrate, which yields only 41% elemental choline[80]. Nevertheless, despite this apparent superiority in choline delivery, choline chloride is less than optimal for dietary supplementation in humans. This is because, akin to choline bitartrate, it contributes to the production of TMAO. Consequently, while its high choline content appears promising, the combination of poor palatability and TMAO-related risks renders choline chloride an impractical choice.

The absorption of choline from bitartrate and chloride forms hinges on their dissociation into free choline, which is transported across the intestinal epithelium. Research suggests that bioavailability may plummet to as low as 20% in certain cases, influenced by factors such as gut microbiota composition, intestinal pH, and genetic variations in choline transporter expression[81]. This variability complicates the reliability of these supplements, particularly when precise dosing is critical, as in prenatal nutrition where fetal brain development depends on consistent maternal choline availability.

Lecithin, typically derived from soy or sunflower, contains a mixture of phospholipids, with PC being the primary component[2]. However, due to its botanical origin, the acyl chains of these phospholipids are enriched in LA. The implications of excessive LA consumption will be addressed in a subsequent section of this manuscript. Although lecithin’s choline is bioavailable, its concentration remains modest, with PC comprising approximately 20%–35% of lecithin’s weight, and choline constituting 13%–14% of PC, resulting in a total choline content of only 2.6%–4.9% by weight.

Lecithin's limited choline yield, a long-recognized issue in nutritional science, poses challenges in meeting daily choline requirements efficiently. Only 75% of lecithin's choline is biologically available, requiring 16.7 to 25.6 g (about two tablespoons of granules) to achieve the recommended 500 mg daily intake[82]. This substantial amount not only presents a practical hurdle but also introduces a high intake of LA. Similarly, while choline bitartrate and choline chloride effectively raise plasma choline levels, they raise safety concerns due to TMAO production[83,84]. Consequently, despite the benefits of PC, lecithin’s modest choline concentration and high LA content, combined with the safety issues of other choline sources, underscore its inefficiency as a primary choline source.

Citicoline is a watersoluble cytidinediphosphate ester that is about 95% orally bioavailable and almost completely absorbed via the sodiumcoupled choline transporter. Once hydrolyzed, free choline increases plasma levels while cytidine is rapidly converted to uridine, boosting denovo PC and PE synthesis through the Kennedy pathway[10]. Citicoline preserves cardiolipin, mitigates lipid peroxidation, and stabilizes mitochondrial membranes in both hepatic and neural tissues[85]. Importantly, citicoline circumvents gut microbial TMA formation, producing negligible circulating TMAO[80].

αGPC is a deacylated PC derivative containing about 40% choline by weight. A stableisotope tracer trial in healthy adults showed that αGPC delivers proportionally more labelled choline into hepatic PC pools but produces a lower peak of free plasma choline than citicoline, suggesting slower firstpass clearance yet efficient phospholipid incorporation[86]. In contrast to citicoline, αGPC undergoes partial microbial demethylation to TMA and elevates fasting TMAO in humans[87]. A Korean national cohort (n = 12 million) linked ≥ 2 months of αGPC prescriptions to a 46% higher 10year incident stroke risk after multivariable adjustment, implicating TMAOmediated vascular effects[9]. Nevertheless, a 2023 systematic review concluded that shortterm, αGPC remains effective and generally welltolerated for cognitive impairment[87].

This has important practical implications: Citicoline provides a dual phospholipid benefit (PC + PE) with minimal TMAO burden, making it the preferred therapeutic backbone for addressing the PC/PE imbalance described earlier. αGPC may be reserved for shortcourse cognitive support when rapid brain ACh replenishment is desired, but should be avoided in individuals with elevated vascular risk until additional longterm safety data emerge.

Table 3 provides a head-to-head comparison of citicoline and α-GPC across critical pharmacokinetic and safety metrics. While both exhibit excellent oral bioavailability (about 95% and about 85%, respectively), citicoline demonstrates superior plasma choline kinetics and, crucially, minimal TMAO production compared to α-GPC's moderate elevation. The 46% increased stroke risk associated with chronic α-GPC use underscores the clinical relevance of selecting choline donors with favorable vascular safety profiles.

Table 3 Comparative pharmacokinetics and safety profile of citicoline vs α-glycerophosphocholine.

Metric	Citicoline	α-GPC	Key takeaway
Elemental choline	18%-19%	40%-41%	α-GPC more choline-dense
Oral bioavailability	Approximately 95%	Approximately 85%	Both excellent
Peak plasma free choline (500 mg eq)	↑2.6-fold vs baseline[10]	↑1.8 fold vs baseline[86]	Citicoline faster spike
Effect on hepatic PC/PE	↑PC + PE balance[85]	↑PC preferentially[86]	Citicoline broader scope
TMAO production	Minimal[80]	Moderate↑[87]	Clinically relevant
Long-term vascular signal	Neutral (no association)	+46% 10 years stroke risk[9]	Use cautiously

PC/PE: Phosphatidylcholine/phosphatidylethanolamine; TMAO: Trimethylamine-Noxide; α-GPC: Αglycerophosphocholine.

CITICOLINE, THE IMMEDIATE PC PRECURSOR: THE PREFERRED CHOLINE SUPPLEMENT

In my initial analysis of the data for this paper, an overreliance on established knowledge led to a significant error: The premature dismissal of citicoline, a compound overlooked due to the unfounded assumption that factors beyond my immediate expertise lacked scientific merit. This oversight is not unique; many in the field may have similarly overlooked citicoline as a choline supplement, despite its benefits, which could position it as a leading option if further prioritized in research and application. Citicoline’s surprisingly limited popularity likely stems from practical challenges, including its low choline content of only 21% by weight, necessitating multiple daily capsules, and compliance challenges, as historically, supplements with higher bioavailability have been favored. This highlights a pervasive flaw in scientific inquiry—the tendency to prioritize familiar frameworks over emerging or less conventional contributors.

To correct this, researchers must evaluate data with humility and rigor, systematically assessing all plausible factors, including citicoline, irrespective of their alignment with prior knowledge. Overfamiliarity can obscure the potential of compounds like citicoline, which may yield valuable insights when explored thoroughly. My original dismissal of citicoline exemplifies this risk, as it could have led to errors that a more open-minded approach would have avoided. This revision underscores a key principle: Unfamiliar elements should not be presumed insignificant merely because they diverge from tradition. By incorporating citicoline and acknowledging its potential, researchers can base their conclusions on comprehensive, evidence-based reasoning. This approach reduces the risk of overlooking critical contributors and strengthens the scientific process.

Having established the necessity of such inclusive inquiry, it is pertinent to examine citicoline’s biochemical significance and therapeutic promise, which underscore why its initial oversight was a serious misstep. Citicoline, scientifically designated as cytidine-5’-diphosphocholine (CDP-choline), was identified in the 1950s by Eugene Kennedy as the immediate precursor in the biosynthesis of PC[10]. Present in minute amounts within mammalian cells, citicoline was successfully synthesized in 1956 and by the 1970s had evolved into a commercially available therapeutic agent, with a historical emphasis on its exploration for neurological applications as it has been shown to have neuroprotective properties and enhance cognitive performance, particularly in individuals with compromised brain function[88].

The association of citicoline with neurological conditions emerged from early clinical investigations in the historical emphasis in neuropharmacological research in the 1970s for cerebral ischemia[89]. A seminal human study in the 1980s demonstrated that its administration improved cognitive recovery in ischemic stroke patients[90]. This foundational research, coupled with trials targeting Alzheimer’s disease and traumatic brain injury, established citicoline as a promising neurotherapeutic agent[91-94]. Consequently, subsequent studies reinforced this trajectory, creating a self-perpetuating focus of its applications in brain-related outcomes.

Citicoline, frequently highlighted for its neurological efficacy, is recognized for its capacity to augment ACh[95]. However, this attribute is not unique to citicoline, as it undergoes hydrolysis into choline and cytidine. The choline moiety then serves as a substrate for ACh biosynthesis-a pathway shared by all PC precursors. This perception of uniqueness may be exaggerated, in part because its name closely resembles that of choline, reinforcing the mistaken belief that citicoline alone supports ACh synthesis. In contrast, the mechanistic overlap with other choline donors underscores that citicoline’s effect on cholinergic transmission represents a shared biochemical property rather than an exclusive therapeutic advantage. Thus, while citicoline remains a valid option for cholinergic supplementation, its role in ACh modulation does not confer a singular distinction over comparable precursors.

While citicoline’s impact on ACh modulation is significant, its broader effects on cellular health, particularly membrane support, are often underemphasized due to several contributing factors. First, the rapid, quantifiable cognitive enhancements linked to ACh production align with clinical priorities and research methodologies, whereas membrane-related benefits manifest gradually and lack dramatic endpoints. Second, decades of accumulated neurological data have entrenched this focus, overshadowing emerging evidence of broader applications. Additionally, market dynamics exacerbate this disparity; the consumer demand for cognitive enhancement, as demonstrated by the widespread use of nootropic supplements, emphasizes the role of ACh over the less commercially prominent, yet biologically vital, function of maintaining cellular homeostasis by enhancing membrane integrity and function.

Citicoline is commonly administered orally in encapsulated or powdered formulations, with therapeutic dosages ranging from 500 to 2500 mg per day. However, its notably bitter taste, a longstanding barrier to patient adherence, has prompted newer efforts to improve compliance through advanced formulation techniques. Specifically, recent innovations have focused on converting citicoline powder into a microencapsulated form, a process in which the powder is coated with a biocompatible polymer to mask its aversive flavor. This microencapsulated citicoline, which retains its bioavailability, can be seamlessly incorporated into food matrices.

Citicoline undergoes hydrolysis into choline and cytidine, which are subsequently integrated into the glycerol-3-phosphate backbone of phospholipids. Cytidine is then metabolized into uridine within hepatocytes, which serves as a substrate in the Kennedy pathway, facilitating the synthesis of PE[96]. This dual role in generating both PC and PE is one of the primary reasons citicoline is so valuable in therapeutic contexts. By facilitating the synthesis of both primary phospholipids, citicoline helps maintain the vitally important PC/PE ratio.

Citicoline’s capacity to enhance PC and PE synthesis underscores a therapeutic potential that extends well beyond its established neurological applications. Its systemic influence on membrane health also supports diverse physiological systems; for instance, it promotes hepatoprotection by mitigating lipid dysregulation in fatty liver disease and bolsters cardiovascular function by enhancing cardiomyocyte resilience against oxidative stress. Despite these benefits, citicoline’s adoption remains limited, likely due to compliance challenges associated with its low choline content. Citicoline’s pivotal role in optimizing the PC/PE ratio likely harbors numerous as-yet-unexplored benefits, warranting further investigation into its therapeutic versatility.

Table 4 compares the choline content and bioavailability of common supplemental forms. These distinctions are critical for selecting appropriate formulations in clinical or therapeutic contexts.

Table 4 Comparison of choline supplement forms¹.

Supplement form	Choline content	Bioavailability
Choline bitartrate	40%	20%
Choline chloride	74%	20%
Phosphatidylcholine	Approximately 13% (varies by source)	Moderate (Approximately 60%)
Citicoline (cytidine diphosphate-choline)	21%	High (> approximately 90%)

¹Comparative analysis of choline supplement forms by elemental choline content and estimated bioavailability. Choline chloride contains the highest proportion of choline by weight but is poorly absorbed. Citicoline (cytidine diphosphate-choline) stands out for its high bioavailability, making it an efficient source despite its lower choline density. Phosphatidylcholine, while lower in choline content, may offer additional functional benefits related to membrane structure and lipid metabolism.

RECONCEPTUALIZING FATTY LIVER DISEASE

Fatty liver disease, a term that collectively encompasses conditions historically delineated as NAFLD/MASLD and alcoholic liver disease, has surged to epidemic proportions and represents a burgeoning public health challenge in the United States. The current epidemiological landscape shows a high prevalence, with estimates approximating nearly half (47.8%) of the adult population[1]. Table 5 outlines the prevalence of fatty liver disease across major United States population groups based on NHANES data from 2017–2018. Hispanics exhibit the highest rates at 63.7%, followed by non-Hispanic whites at 56.8%. Non-Hispanic Blacks show the lowest prevalence at 46.2%, despite a comparable or higher burden of metabolic risk factors[97]. These rates reflect the powerful damaging influence of obesogenic environments and metabolic dysregulation, historically prioritized as key drivers of hepatic steatosis (Table 5).

Table 5 Prevalence of fatty liver disease¹.

Population group	Prevalence (%)	Notes
Hispanics	63.7	Highest in Hispanics
Non-Hispanic whites	56.8	Second highest
Non-Hispanic blacks	46.2	Lower prevalence
Overall United States adults	47.8	National average

¹Prevalence of fatty liver disease among United States adults, based on National Health and Nutrition Examination Surveys 2017–2018 data. Hispanics show the highest rate at 63.7%, followed by non-Hispanic whites at 56.8%, non-Hispanic blacks at 46.2%, and a national average of 47.8%. These disparities, which reflect metabolic differences and dietary habits rich in linoleic acid, underscore the status of fatty liver disease as a public health challenge.

This alarming prevalence underscores the urgency of reevaluating the nomenclature and pathophysiology of hepatic steatosis. Recent updates in terminology-most notably the shift to MASLD-reflect growing scientific consensus that metabolic dysfunction, rather than alcohol exclusion, defines the condition’s core pathology. Yet this traditional divide between alcoholic and nonalcoholic causes obscures a shared metabolic foundation—prompting a shift toward the unifying term “fatty liver disease”. Extrinsic fructose, dissociated from its native whole-food matrix, also exerts a substantive influence in fatty liver disease[98]; however, the pivotal convergence of these etiologies resides in their shared induction by mitochondrial toxicants-specifically LA in non-alcoholic manifestations and ethanol in alcoholic variants-both culminating in a unified pathway of mitochondrial impairment.

In NAFLD/MASLD, excessive dietary LA undergoes peroxidation to yield toxic metabolites such as 4-HNE, a reactive aldehyde that disrupts mitochondrial membrane integrity and impairs oxidative phosphorylation[99]. Similarly, ethanol metabolism generates acetaldehyde, another reactive aldehyde that inflicts comparable mitochondrial damage, evidenced by elevated ROS and diminished ATP synthesis[100]. Thus, despite divergent triggers, the resultant hepatic injury-characterized by triglyceride accumulation and steatohepatitis—bears striking similarity, challenging the validity of their historical separation.

Amid a burgeoning public health crisis, the United States has experienced a dramatic surge in alcohol-related mortality over the past two decades, with rates escalating approximately twofold-an alarming trend substantiated by national health statistics[101]. This escalation is exacerbated by the synergistic interplay of prevalent comorbidities, notably overweight, obesity, and diabetes, each of which independently contributes to hepatic pathology through mechanisms such as steatosis and inflammation. Given the scarcity of viable alternative interventions, the prevalence of self-medication behaviors-often aimed at alleviating adverse psychological or physiological states-is notably elevated, underscoring the urgency for targeted clinical interventions informed by the convergence of metabolic and dietary stressors.

These risk factors, coupled with alcohol consumption, may precipitate an additive effect, accelerating the onset of liver damage and subsequent mortality. In this context, the modern dietary landscape introduces an additional layer of complexity, characterized by ubiquitous exposure to LA-rich industrially processed oils, which have elevated LA intake to unprecedented levels-estimated at 7%-8% of total energy in Western populations, far surpassing physiological thresholds. This excessive LA consumption amplifies the generation of oxidative byproducts, such as 4-HNE[102], which, in conjunction with acetaldehyde derived from alcohol metabolism, induces mitochondrial dysfunction and hepatic lipid overload. Figure 2 illustrates the converging mechanisms by which LA and ethanol promote mitochondrial toxicity. Together, these insults compromise the ETC and reduce ATP production, undermining cellular energy metabolism at its core.

Figure 2 Mechanism of mitochondrial toxicity induced by linoleic acid and ethanol. This schematic illustrates the synergistic mechanisms by which LA and ethanol induce mitochondrial toxicity, leading to cellular dysfunction. LA undergoes peroxidation to generate reactive oxygen species, such as hydroxyl radicals (OH), and lipid radicals (L). These reactive intermediates, in the presence of molecular oxygen (O₂), further propagate the formation of lipid peroxyl radicals (LOO). Subsequently, lipid peroxides (LOOH) are produced, which can be exacerbated by hydrogen ions (H⁺). In this context, lipid peroxides may undergo Hock cleavage or β-scission, yielding secondary products like 4-hydroxynonenal, a highly reactive aldehyde known to impair mitochondrial membrane integrity. These stressors inhibit the electron transport chain, notably Complex III, reducing adenosine triphosphate synthesis. Vitamin E’s role in neutralizing lipid peroxyl radicals is also shown.

Consequently, fatty liver disease emerges as a spectrum of mitochondrial pathology rather than a binary classification[103]. For instance, comprehensive reviews published in the last two years have demonstrated the role of LA-derived aldehydes in exacerbating insulin resistance and hepatic inflammation, key hallmarks of metabolic diseases[104]. These findings, coupled with evidence of acetaldehyde’s parallel effects on mitochondrial bioenergetics, highlight the physiological significance of dietary and metabolic interventions. In this context, the liver’s role as the body’s principal detoxification organ-reliant on membrane stability and phospholipid synthesis-becomes critically impaired, further compounding the therapeutic challenge. As such, addressing this escalating public health crisis demands a unified approach to fatty liver disease, one that transcends outdated distinctions and targets the mitochondrial underpinnings of this pervasive disorder.

Glossary of Core Mitochondrial Terms: Protonmotive force (Δp)-The electrochemical gradient generated by the ETC; mathematically Δp = Δψm + (59 mV × ΔpH)[105]. Mitochondrial membrane potential (Δψm)–The electrical component of Δp (= −150 to −180 mV in hepatocytes); collapse of Δψm halts ATP synthesis and favors ROS generation[106]. ATP synthase (FOF1)–Rotary nanomotor that converts Δp into ATP; its catalytic βsubunits are directly driven by proton flow[107]. Uncoupling / proton leak: Return of protons through the inner membrane independent of ATP synthase; regulated by uncoupling proteins and pathological lipid peroxidation products[108]. βoxidation–Stepwise removal of twocarbon units from fattyacylCoA within the mitochondrial matrix, yielding nicotinamide adenine dinucleotide (reduced form) and flavin adenine dinucleotide (reduced form) (NADH/FADH2) that feed into the ETC[109] (Figure 2).

Having established that fatty liver disease may be reconceptualized as a mitochondrial disorder responsive to targeted intervention, we now turn to explore the therapeutic potential of strategies aimed at modulating phospholipid metabolism and reducing mitochondrial toxin burden. This approach, which integrates the enhancement of PC and PE biosynthesis with the deliberate reduction of LA and ethanol exposure, emerges as a radical, yet mechanistically sound paradigm for the near elimination of hepatic steatosis. Although large-scale clinical trials validating this precise regimen remain forthcoming, the anticipation of its success is anchored in a confluence of robust physiological mechanisms, supported by mounting empirical evidence and a nuanced understanding of lipid-mitochondrial interplay. The next section reviews the possible mechanisms underpinning this strategy, weaving a narrative that bridges molecular insights with therapeutic promise.

ADDRESSING THE CHOLINE CONUNDRUM: AN ADVANCED APPROACH TO HEPATIC OPTIMIZATION

The quest to optimize choline intake has long been hampered by the limitations of dietary sources and conventional supplementation strategies. Choline remains inadequately consumed by the vast majority of the population. NHANES data from 2009–2012, substantiated by supporting reviews, reveal that over 90% of individuals-particularly pregnant women (91.49%) and females (93.9% in specific analyses)-fail to achieve the AI for choline[7]. The low sufficiency of choline intake is likely related to the difficulty in consuming adequate amounts through diet alone. Achieving these thresholds through diet demands substantial daily consumption of choline-rich foods, such as four egg yolks (approximately 500 mg choline) or 16 ounces of red meat (approximately 515 mg choline)-a feat impractical for most.

Compounding this challenge, commercially available choline supplements are frequently underdosed or inefficiently absorbed, with over 75% of the administered dose failing to reach systemic circulation. Instead, much of this unabsorbed choline is metabolized by gut microbiota into TMA, which is subsequently oxidized in the liver to TMAO which is implicated in elevated cardiovascular risk. Thus, an important question emerges: How can we surmount these barriers to deliver therapeutic levels of choline effectively and safely?

HEPATIC PC METABOLISM AND THE ROLE OF MICRONUTRIENTS

Central to this therapeutic vision is the augmentation of PC synthesis. Hepatic steatosis, characterized by triglyceride accretion exceeding 5% of liver weight, arises in part from impaired VLDL secretion, a process historically linked to choline insufficiency[110]. By upregulating PC availability-achievable through dietary choline supplementation or stimulation of the PEMT pathway—hepatocytes regain their capacity to package and export triglycerides into the circulation, thereby alleviating intracellular lipid burden[33,111-113]. Figure 3 illustrates the critical role of choline, through its metabolite PC, in the hepatic assembly and export of VLDL.

Figure 3 Role of choline in verylowdensity lipoprotein assembly and lipid export. This schematic illustrates choline’s role, via phosphatidylcholine (PC), in verylowdensity lipoprotein (VLDL) assembly and lipid export within a hepatocyte. The hepatocyte, depicted with a jagged plasma membrane, contains a central nucleus (light orange) and an endoplasmic reticulum (ER, orange) where PC (purple box) facilitates initial VLDL assembly. Lipid droplets (yellow circles) contribute triglycerides to VLDL, which matures in the Golgi apparatus (light purple) before export into the bloodstream (red). Green VLDL particles, marked with "PC Enables Triglyceride Export", highlight PC’s role in lipid secretion. Arrows trace the pathway from ER to Golgi to bloodstream, emphasizing the sequential process of VLDL biogenesis and hepatic lipid clearance. VLDL: Verylowdensity lipoprotein; PC: Phosphatidylcholine.

In the 1950s, Eugene Kennedy and his collaborators conducted pioneering research that elucidated the fundamental framework of numerous phospholipid biosynthetic pathways. Notably, their work revealed that cytidine triphosphate (CTP), rather than the more commonly utilized ATP, serves as the essential substrate for the biosynthesis of key phospholipids such as PC and PE[114]. This finding was unexpected, as ATP is typically the primary energy currency in cellular metabolism, thereby highlighting the distinct biochemical pathways involved in membrane lipid production.

This foundational work by Kennedy enabled the discovery of specific phospholipid biosynthetic pathways, such as those for PC in hepatocytes. The biosynthesis of PC within hepatocytes proceeds via two primary pathways: The CDP-choline pathway and the PEMT pathway[115]. The CDP-choline pathway, which accounts for approximately 70% of hepatic PC production, relies on the sequential action of choline kinase, CTP: Phosphocholine cytidylyltransferase, and CDP-choline: 1,2-DAG choline phosphotransferase. In contrast, the PEMT pathway utilizes PE and three methyl groups donated by SAM, derived from the essential amino acid Met, to synthesize PC[116]. Figure 4 contrasts the structural and functional differences between a healthy hepatocyte and one affected by choline deficiency. In the healthy liver cell (left), intact mitochondria and functional VLDL export support normal lipid balance, with minimal intracellular fat. In the steatotic liver cell (right), choline deficiency impairs VLDL assembly, leading to intracellular triglyceride accumulation, mitochondrial damage, and disrupted membrane integrity. This side-by-side comparison highlights choline’s essential role in maintaining hepatic lipid homeostasis and preventing steatosis (Figure 4).

Figure 4 Impact of choline deficiency on liver function. This figure juxtaposes a healthy hepatocyte (left, green) with a steatotic hepatocyte (right, red) to depict the consequences of choline deficiency. The healthy hepatocyte features a smooth plasma membrane, sparse lipid droplets (yellow, < 5% of cell volume), intact mitochondria (orange), and an outward arrow indicating robust verylowdensity lipoprotein (VLDL) export, reflecting efficient triglyceride clearance. In contrast, the steatotic hepatocyte exhibits a disrupted membrane, excessive lipid accumulation (dense yellow droplets exceeding 5% of liver weight), damaged mitochondria, and impaired VLDL assembly. This comparison underscores choline’s pivotal role in hepatic lipid homeostasis, where its deficiency precipitates steatosis—a condition historically linked to diets low in methyl donors. VLDL: Verylowdensity lipoprotein.

The PEMT pathway, though less dominant, is particularly relevant in conditions of choline deficiency, capable of contributing up to 30% of PC under such circumstances. To optimize these processes, a targeted supplementation strategy must incorporate not only choline and ethanolamine, but also Met, folate, and vitamin B12-cofactors integral to methylation reactions. For instance, folate and B12 facilitate the regeneration of SAM via the Met cycle, ensuring a robust methyl donor supply for PEMT-mediated PC synthesis[117].

Furthermore, the provision of these cofactors supports the synthesis of PE, thereby bolstering comprehensive membrane integrity. This dual-target approach-enhancing both PC and PE production-addresses a fundamental aspect of cellular homeostasis often overlooked in conventional supplementation. As the body’s principal detoxification organ, the liver also processes xenobiotics and endogenous waste, a function reliant on membrane stability.

Although extrahepatic tissues participate in PC biosynthesis, the liver emerges as the predominant contributor due to its utilization of dual metabolic pathways-the CDP-choline and PEMT routes-coupled with its substantial synthetic capacity and systemic dissemination through lipoprotein particles. These pathways, historically elucidated through studies of lipid metabolism, enable the liver to produce PC at a rate that likely constitutes 50%-70% of the total body pool. In this context, while tissues such as the lung, which generates dipalmitoyl-PC for surfactant, and the brain, which forms PC for neuronal membranes, contribute locally, their output is comparatively limited. Furthermore, the liver’s unique ability to leverage the PEMT pathway, accounting for roughly 30% of its PC synthesis, enhances its role under conditions of choline scarcity[118].

MECHANISTIC SYNERGY AND ANTICIPATED THERAPEUTIC EFFICACY

Parallel to the enhancement of phospholipid metabolism, the reduction of mitochondrial toxins-namely LA and ethanol-addresses the upstream drivers of mitochondrial dysfunction, a keystone in the pathogenesis of fatty liver disease. LA, pervasive in contemporary diets, undergoes lipid peroxidation to yield reactive aldehydes such as 4-HNE, which adduct to mitochondrial proteins, impairing Complexes I and III of the ETC. By curtailing dietary LA intake this oxidative insult is diminished, preserving mitochondrial integrity and enhancing fatty acid β-oxidation[104]. Ethanol, a well-characterized hepatotoxin, exerts analogous mitochondrial toxicity through its metabolite acetaldehyde, which inhibits pyruvate dehydrogenase and disrupts the tricarboxylic acid cycle[5,119]. Abstinence or significant reduction in ethanol consumption thus alleviates this metabolic bottleneck, restoring mitochondrial capacity to oxidize accumulated lipids.

The anticipated efficacy of this dual-pronged strategy-enhancing PC and PE synthesis while minimizing LA and ethanol-rests on its capacity to address both the proximate cause of steatosis, impaired lipid export, and its ultimate mitochondrial underpinnings. Table 6 outlines the dual mechanisms underlying the proposed therapeutic strategy for fatty liver disease. By bolstering PC and PE availability, hepatocytes can efficiently sequester triglycerides into VLDL particles, reducing cytosolic lipid pools susceptible to peroxidation. Simultaneously, the attenuation of LA and ethanol-derived aldehydes preserves mitochondrial oxidative capacity, enabling the catabolism of excess fatty acids that would otherwise perpetuate steatosis. This synergy is poised to disrupt the vicious cycle of lipid accumulation and organellar stress (Table 6).

Table 6 Mechanisms of action for the proposed therapeutic strategy¹.

Mechanism	Description	Therapeutic outcome
Enhancing PC via choline supplementation	Utilizes delivery of choline to augment PC biosynthesis via the cytidine diphosphate-choline and PEMT pathways	Increases VLDL assembly, improves hepatic lipid export, reduces intracellular triglyceride accumulation
Reducing mitochondrial toxins (linoleic acid and ethanol)	Minimizes exposure to linoleic acid and ethanol, reducing formation of 4-hydroxynonenal and acetaldehyde	Decreases mitochondrial damage, preserves electron transport chain function, and improves adenosine triphosphate production

¹This table outlines the dual mechanisms of a novel therapeutic approach for fatty liver disease. First, choline delivery enhances phosphatidylcholine synthesis via the cytidine diphosphate-choline and PEMT pathways, boosting verylowdensity lipoprotein assembly and reducing hepatic triglyceride levels by up to 30%, as evidenced in preclinical models. Second, minimizing mitochondrial toxins—such as linoleic acid and ethanol—decreases reactive aldehyde formation (e.g., 4-hydroxynonenal), thereby preserving β-oxidation and mitochondrial integrity. This strategy integrates decades of lipid metabolism research, offering a comprehensive approach to restore hepatic function.

PC: Phosphatidylcholine; VLDL: Verylowdensity lipoprotein.

Moreover, this approach holds promise for reversing the metabolic consequences of fatty liver disease, including insulin resistance and systemic inflammation. Enhanced lipid clearance further improves hepatic insulin signaling, an important step toward ameliorating the broader metabolic syndrome[120,121]. While the novelty of this integrated strategy precludes definitive clinical validation, its mechanistic coherence and preliminary successes in analogous interventions—such as choline-enriched diets in cohorts with fatty liver disease—provide a compelling rationale for optimism[121-124]. While translating this conceptual framework into therapeutic reality requires rigorous investigation, the mechanistic insights outlined here provide a clear path forward. The integration of phospholipid modulation with toxin reduction offers a holistic assault on fatty liver disease, targeting its molecular origins with precision.

EARLYPHASE CLINICAL EVIDENCE: METHODS, KEY FINDINGS, AND REMAINING QUESTIONS

A small but informative body of earlyphase human research lends provisional support to our mechanistic hypothesis yet also reveals important gaps. Three controlled studies merit close attention. The most rigorous dietary manipulation to date is the 16week, fully provisioned randomized trial by Courville et al[125] in 38 women with overweight or obesity, in which LA intake was reduced to about 2% of energy. Plasma LA fell by 41%; however, neither redbloodcell arachidonic acid nor circulating endocannabinoids declined, and liver fat was not imaged, leaving hepatic outcomes unresolved.

In contrast, the LIPOGAIN over-feeding study enrolled 39 normalweight adults and provided excess calories as either LArich sunflower oil or palm oil for seven weeks. Despite identical weight gain, the saturatedfat arm increased liver fat by 32% on MRIprotondensityfatfraction, whereas the polyunsaturatedfat arm showed no significant change[126]. These results suggest that LA reduction per se does not worsen steatosis, but the short duration and overfeeding design limit therapeutic extrapolation.

Choline’s hepatic effects have been examined only in patients on longterm total parenteral nutrition (TPN): Buchman et al[7] randomized 15 such individuals to intravenous choline chloride 2 g/day or placebo for six weeks. Choline repletion normalized plasma choline, reduced alanine ALT by about 50%, and halved intrahepatic fat on CT scans. However, the parenteral route of administration and severe baseline deficiency restrict generalizability to community populations. Across these studies, three limitations stand out: (1) Small sample sizes (n ≤ 39); (2) Short followup (< 4 months); and (3) Incomplete phenotyping—only one included liver imaging and none reported fibrosis markers or clinical endpoints. Crucially, no randomized study has evaluated chronic oral choline supplementation in biopsyproven NAFLD or NASH. Addressing these evidence gaps should be prioritized before broad clinical implementation of our combined LAreduction and choline optimization strategy.

Collectively, early human trials suggest that both LA toxicity and choline deficiency contribute to NAFLD pathogenesis. Choline replacement, even in severely depleted TPN patients, rapidly normalized serum ALT and reduced hepatic fat, confirming the essential role of this nutrient in liver health. More recently, a 12 week randomized trial in adults with biopsyconfirmed NAFLD demonstrated that daily supplementation with a nutraceutical blend providing about 550 mg of choline chloride, PC and docosahexaenoic acid reduced ultrasoundderived steatosis scores and improved ALT relative to placebo, even in the absence of weight loss[127].

Mechanistic data provide further insight. Genomeediting and multiomics studies have identified TramLag1CLN8Domain–containing 1 and 2-which encode small, membranebound acyltransferase enzymes—as regulators of PE acylchain composition. Hepatic overexpression of these genes skews mitochondrial membranes towards saturated PE species and accelerates the transition from simple steatosis to inflammatory NASH in mice[128]. Conversely, endurancestyle exercise in rodent NASH models restores the hepatic mitochondrial phospholipidome, normalizes Δψm and rescues respiratory capacity, highlighting the plasticity of this lipid compartment[129]. These findings support the hypothesis that an optimal PC: PE ratio is necessary for electrontransport supercomplex stability and efficient βoxidation.

The oxidative burden imposed by LA is an equally important, but often underappreciated, pathogenic driver. LA-derived lipid peroxides such as 4-HNE covalently modify cytochrome c oxidase subunits, impairing complex IV respiration. Diets high in LA and its oxidized metabolites synergize with ethanol to intensify hepatic inflammation and injury in animal models-despite caloric and fat-matched saturated fat controls[130]. These findings support clinical observations that seed oil–rich diets and chronic alcohol intake collapse mitochondrial energetics and drive steatosis.

Interestingly, not all LA derivatives are harmful. A microbial metabolite of LA, 10-hydroxy-12-octadecenoic acid, was recently shown to dampen transforming growth factor beta signaling in hepatic stellate cells and reduce fibrosis in high-fat-fed mice[131]. This highlights how the therapeutic potential of manipulating LA metabolism—whether through dietary restriction, probiotic augmentation, or postbiotic administration—could tilt the balance away from toxic aldehyde generation and towards hepatoprotective pathways.

Choline requirements also appear to vary by genotype. A specific single nucleotide polymorphism in the PEMT gene (V175M) reduces endogenous PC synthesis and is associated with lean NAFLD. Individuals carrying this variant may require higher or even parenteral choline dosing[132]. Precision nutrition approaches that screen for PEMT and one-carbon cycle variants could identify “choline obligate” subgroups most likely to benefit from targeted repletion.

Taken together, the evidence positions NAFLD as a choline-responsive, toxin-exacerbated mitochondrial disorder. Repletion with highbioavailability choline donors-citicoline or αGPC-addresses the PC bottleneck that impairs VLDL export, while lowering dietary LA and abstaining from ethanol remove the oxidative triggers that overwhelm hepatic mitochondria. Factorial trials that combine: (1) Citicoline ≥ 1 g/day with cofactor support; and (2) LA restriction to < 4% are now justified to test whether this dualtarget approach can deliver durable histological remission.

Limitations

Despite the promising mechanistic rationale and preliminary evidence reviewed, several constraints temper the strength and generalizability of our conclusions. First, the clinical database for citicolineplusLA restriction remains slim: Only two small phase II trials and several uncontrolled pilot studies have reported liverfat or metabolic endpoints, none exceeding 24 weeks or enrolling more than 100 participants. Larger, longerterm, randomized trials that stratify for sex, age, ethnicity, baseline choline status, and PEMT genotype are essential to confirm durability of benefit and identify responder subgroups. Second, most mechanistic insights derive from rodent models that employ supraphysiological LA loads or ethanol gavage. These paradigms may exaggerate mitochondrial damage relative to typical human exposures and cannot reproduce complex dietary patterns, polypharmacy, or comorbidities that shape fattyliver progression in clinical practice. Third, our narrative format—though useful for hypothesis generation—lacks the systematic search and riskofbias grading required to minimize selection bias. Inevitably, some negative or neutral studies may have been missed, and publication bias may overstate effect sizes.

Fourth, key safety questions remain unresolved. Citicoline has an excellent neurologic safety record, but highdose, chronic use for hepatic indications (> 2 g/day) has never been systematically evaluated for renal, cardiovascular, or neuroendocrine sequelae, nor has its interaction with methyldonor cofactors or concurrent lipidlowering drugs. Likewise, aggressive dietary LA restriction to < 4% of energy could inadvertently reduce intake of essential ω6 precursor linolenic acid (18:2 n6) and lipidsoluble vitamins unless carefully balanced with wholefood sources of micronutrients. Beyond dosage and formulation, interpretation of clinical findings also warrants caution due to biological and environmental confounders that can markedly influence choline metabolism and hepatic outcomes. First, gut microbiota composition determines the fraction of ingested choline that is absorbed vs shunted to TMA and its pro-steatotic oxidation product TMAO; dysbiotic, cutC/D-enriched communities can therefore blunt choline bioavailability while exaggerating TMAO exposure, obscuring therapeutic effects or inflating harms[133]. Second, concurrent contact with environmental hepatotoxins-most prominently heavy metals such as cadmium in drinking water or rice[134], and endocrine-disrupting bisphenols leached from plastics[135]-can synergize with excess LA and ethanol to intensify mitochondrial stress, lipid peroxidation, and inflammatory signaling. Future trials should therefore include baseline metagenomic or 16S profiling plus quantitative assays of metal and persistent organic pollutant burdens, and adjust outcomes accordingly, to isolate choline’s true hepatoprotective potential.

Fifth, realworld implementation is hampered by the practical difficulty of recognizing stealth LA additives (e.g., higholeic seedoil blends) across diverse food environments and by the time burden of manual label scanning. To overcome these ingredient identification barriers, emerging technologies like large language model (LLM) platforms and AIpowered chatbots offer scalable solutions. These tools can: (1) Parse complex ingredient panels in real time; (2) Flag probable highLA additives; and (3) Suggest lowerLA substitutes within a user’s price and taste constraints. Proofofconcept studies have demonstrated that AI nutrition assistants reduce the time needed to identify hidden fats and allergens by 40%–60%, improve labelreading accuracy, and boost users’ confidence in making grocery swaps[136].

Additionally, consumerfacing chatbots integrating barcode scanners with LLMdriven nutrient databases have enhanced adherence to hearthealthy and weightloss diets in randomized usability trials[137]. Embedding LAscreening algorithms into smartphone apps could thus democratize this process, though challenges such as hallucinated ingredient matches, data privacy, and equitable access for lowresource users require further refinement. Collectively, these limitations underscore the need for rigorously powered human trials, standardized LAquantification methods, longterm safety surveillance, and usercentric digital tools before this dual strategy can be confidently recommended at scale.

CONCLUSION

Choline is vital for physiological functions, with its deficiency contributing to fatty liver disease, a pressing public health issue affecting nearly half of United States adults. Traditional supplements like choline bitartrate suffer from poor bioavailability and elevate TMAO, a cardiovascular risk factor. This document proposes a dual strategy: Leveraging effective choline formulations, such as citicoline, to boost phospholipid synthesis (PC and PE) without TMAO production, while minimizing exposure to mitochondrial toxins like LA and ethanol. This approach targets the disease’s mitochondrial roots, enhancing lipid export and reducing oxidative stress. Though large-scale trials are pending, the mechanistic coherence suggests transformative potential for managing fatty liver disease, warranting further research to validate its clinical efficacy.