Obesity paradox in patients with community-acquired pneumonia: Have you fully considered the confounding factors?

Abstract

There exists a notion that there is an obesity paradox in the prognosis of community-acquired pneumonia. In other words, obese individuals with community-acquired pneumonia have a better prognosis. The study by Wang et al supports this claim, but we believe that the obesity paradox should not be proposed hastily as it is influenced by numerous subjective and objective confounding factors.

Key Words: Community-acquired pneumonia; Mortality; Body mass index; Overweight; Obesity paradox

Core Tip: There exists a notion that there is an obesity paradox in the prognosis of community-acquired pneumonia (CAP). Wang et al’s research findings substantiate this statement. However, our analysis reveals that this notion is influenced by numerous confounding factors, including age, chronic pulmonary diseases, and pathogens. Wang et al’s research lacked rigor in defining obesity and insufficient data on confounding factors. Thus, we recommend future research to categorize CAP patients more precisely and consider multiple factors to elucidate the exact role of body mass index in CAP prognosis.

TO THE EDITOR

We have read with great interest the article published by Wang et al[1]. This article indicates that, for patients with community-acquired pneumonia (CAP), the mortality rate is lowest for overweight/obese patients, and highest for underweight patients. We congratulate the authors and wish to present a few comments and suggestions. In their study, the patients were classified into three groups: (1) Underweight [with a body mass index (BMI) of less than 18.5 kg/m²]; (2) Normal weight (with a BMI of 18.5 kg/m² to 23.9 kg/m²); and (3) Overweight/obese (with a BMI of 24 kg/m² or above)[1]. Firstly, the World Health Organization delineates obesity as a state characterized by a BMI of 30 kg/m² or greater[2]. However, this study did not mention how many, or if any, patients met the criteria for obesity; therefore, the conclusions of the study lack rigor. Secondly, we believe that there were insufficient statistical data on the risk factors that could impact the prognosis of the three patient groups, such as their history of chronic pulmonary diseases (asthma, etc.). Undoubtedly, this overlooked an important factor in the respiratory failure of deceased patients. Thirdly, we found that the proportion of underweight patients aged ≥ 65 years was as high as 73.1%, whereas patients in the overweight/obese group were the youngest among the three groups. Age is considered one of the admission criteria for CAP patients (Confusion-Urea-Respiration-Blood pressure-65 score); thus, it is easy to believe that age has a greater impact on the prognosis of pneumonia patients than BMI[3]. Is this, therefore, the major reason for reaching this research conclusion?

IMPACT OF BMI

After reviewing an extensive body of clinical research, we found that a meta-analysis suggested that the mortality rate of CAP patients was not influenced by BMI[4]. In some studies, a linear relationship between the mortality rate of pneumonia and BMI was not demonstrated[5]. The obesity paradox has been questioned and the limitations of using BMI to define body nutritional status have been pointed out[6]. However, there are also some researchers who support the author’s viewpoint[7,8]. In general, there is indeed a notion of the obesity paradox, with many possible hypotheses regarding its underlying causes, which require further substantiation. Here, we intend to analyze plausible reasons for this paradox from a clinical standpoint. Firstly, the relative youthfulness of obese patients in this study might have contributed to the high proportion of low-risk individuals, which reached 73.2%. These individuals were naturally predisposed to a relatively favorable prognosis. Secondly, CAP can be roughly classified into bacterial and viral etiologies. The study included patients who were not suffering from coronavirus disease 2019. Numerous research findings had conclusively demonstrated that obese patients have a worse prognosis for influenza-related pneumonia compared to those of normal weight[9-11]. The study did not explicitly identify pathogens among the different groups, which might also have affected the results. Additionally, obese individuals tend to have more health anxieties, which may prompt them to seek medical attention earlier when experiencing physical discomfort[12]. Doctors also instinctively perceive the heightened risks of adverse outcomes in obese patients, potentially admitting them below the admission criteria and providing them with relatively increased attention and prompt treatment.

CONCLUSION

Therefore, we believe that the paradox of obesity in the prognosis of CAP is influenced by subjective factors and numerous objective clinical factors, which should be drown attention. In the future, it is advisable to categorize patients with CAP based on the different pathogens involved, similar risk factors and medical history, and comparable Confusion-Urea-Respiration-Blood pressure-65 score, in order to adopt appropriate treatment approaches. Large-scale research to further elucidate the exact role of BMI in patients with CAP should also be conducted.