Breastfeeding was associated with lower risks of maternal postpartum hypertension and diabetes mellitus: A systematic review and meta-analysis

Table 1 The characteristics of the 18 included studies, mean ± SD

Ref.	Study design	Study period	Population	Age of all patients (years)	Sample size, (n)	Breastfeeding duration	Follow-up period	Disease reported: Diabetes or hypertension	Data of outcomes (OR/HR)	Adjustment factors
Adam et al[36] (2021), Sudan	Case-control study	May-December 2019	Women with preeclampsia + healthy controls	Median (range) cases: 33.0 (28.0-38.0), controls: 30.0 (25.0-33.0)	348	Yes/No	N/A	Hypertension	Adjusted OR = 0.31 (95%CI: 0.15-0.67)	Age, parity, education level, occupation, history of preeclampsia, history of miscarriage, and BMI
Bajaj et al[37] (2017), Canada	Prospective observational cohort study	Not specified	Women recruited from antepartum GDM screening	≤ 3 months lactation: 34 ± 4, 3-12 months lactation: 35 ± 4, ≥ 12 months lactation: 35 ± 4	330	Breastfed for ≤ 3 months (n = 70), for 3–12 months (n = 140), and for ≥ 12 months (n = 120)	3 years	Diabetes	Lactation for ≥ 6 months: OR = 0.49 (95%CI: 0.24-1.00); Lactation for ≥12 months: OR = 0.37 (95%CI: 0.18–0.78)	Age, ethnicity, family history of diabetes, GDM, and physical activity
Blair et al[38] (2024), United States	Secondary analysis	July 2016-July 2018	Women with recent Gestational Diabetes Mellitus	Not breastfeeding: 31.5 ± 5.7, Breastfeeding: 33.7 ± 5.0	178	Yes/No	8 weeks	Hypertension	Adjusted OR = 0.56 (95%CI: 0.19-1.60)	Age, race/ethnicity, low household income, pre-pregnancy BMI, and weeks since delivery
Gunderson et al[22] (2015), United States	Prospective observational study	August 2008-December 2011	Women diagnosed with GDM	Exclusive formula: 33.0 ± 4.9, mostly formula: 33.4 ± 5.0, mostly breastfeeding: 33.4 ± 4.8, exclusively breastfeeding: 33.5 ± 4.4	1035	Yes/No	2 years	Diabetes	Adjusted HR = 0.53 (95%CI: 0.36-0.77)	Selected groups of baselines, perinatal, and newborn covariates
Gunderson et al[39] (2018), United States	Prospective observational cohort study	1986-2016	Women without diabetes before pregnancy who delivered an infant after baseline	Incident diabetes: 24.2 ± 3.7, no diabetes: 24.0 ± 3.7	1238	Time-dependent lactation duration categories (none, > 0 to 6 months, > 6 to < 12 months, and ≥ 12 months)	30 years	Diabetes	Pool adjusted HR = 0.63 (95%CI: 0.48-0.83)	Examination years (time), race, family history of diabetes, baseline age, fasting glucose, BMI and waist circumference, time dependent GDM, party, physical activity, and dietary quality score
Jäger et al[27] (2014), Germany	Prospective observational cohort study	1994-1998	Women who gave birth	Median (interquartile range) No breastfeeding: 47 ± 15, < 3 weeks of breastfeeding: 46 ± 15, 3 weeks-2 months of breastfeeding: 47 ± 16.5, 2-6 months, 47 ± 17, 6+ months: 49 ± 19	1059	Duration and Yes/No	Not specified.	Diabetes	Adjusted HR = 0.77 (95%CI: 0.47-1.25)	Age, marital status, education, occupation, smoking behavior, etc.
Kim et al[40] (2016), Korea	Cross-sectional	Not specified	Women who gave birth	39.9 (SD not specified)	1053	Yes/No	N/A	Hypertension	Adjusted OR = 0.63 (95%CI: 0.36-1.08)	The first childbirth age, the last childbirth age, gravidity, natural childbirth, and cesarean section
Ley et al[29] (2020), United States	Prospective cohort study	1989-2014	Female registered nurses with a history of GDM	Median age 31.8 (95%CI: 25.2–40.2)	4372	Duration: No breastfeed, 1, 1-3, 4-6, 7-11, 12-17, 18-23, 23-35, 36-47, ≥ 48 months, and cannot remember	87,411 person-years of follow-up	Diabetes	Pool adjusted HR = 1 (95%CI: 0.96-1.04) for lactation	Age, parity, primipara, pre-pregnancy BMI, and age at index GDM diagnosis
Luo et al[41] (2019), United States	Prospective cohort study	1993-1998	Postmenopausal women	Nulliparous: 62.4 ± 7.8, 1-4 parities: 62.8 ± 7.3, 5+ parities: 64.7 ± 6.2	136652	Duration: No breastfeed, 1-6, 7-12, 13-23, and ≥ 24 months	14.2 years	Diabetes	Adjusted HR = 0.88 (95%CI: 0.78-0.99) for < 6-month lactation; adjusted HR = 0.96 (95%CI: 0.92-1.01) for 6 to 12 months’ lactation	Age, race and ethnicity, level of education, BMI, waist circumference, physical activity, smoking, alcohol intake, family history of diabetes, history of hormone therapy use, and age at menopause, etc.
Martens et al[42] (2016) Canada	Retrospective cohort study	1987-2011	Women who gave birth in Manitoba	27.74 ± 5.55	180107	Yes/No	Up to 24 years	Diabetes	Adjusted HR = 0.73 (95%CI: 0.68-0.79)	Age at birth of child, sex, residence, parity, ethnicity, and income
Mazariegos et al[43] (2019), Mexico	Prospective cohort study	2006–2008	Female teachers who are 25 years old and older	0 months: 47.4 ± 6.9, < 3 months: 46.2 ± 7.3, 3-6 months: 45.7 ± 7.2, 6-12 months: 45.0 ± 7.2, > 12 months: 44.4 ± 7.3)	66573	Duration: No breastfeed, 1-6, 7-12, and 13-24 months	157,510 person years of follow-up	Diabetes	Adjusted HR = 0.71 (95%CI: 0.60-0.84) for < 6-month lactation; adjusted HR = 0.81 (95%CI: 0.68-0.97) for 6 to 12 months’ lactation	Age, age at first birth, age at menarche, smoking, diet, physical activity, educational level, socio-economic status, and marital status
Pettitt et al[44] (1997), United States	Prospective cohort study	1950-1978	Women who gave birth	23-65	720	Yes/No	Not specified.	Diabetes	Adjusted OR = 0.41 (95%CI: 0.17-0.98)	Age, birth year (police related), sex, parental diabetes, relative weight, birthweight
Ra et al[47] (2020), Korea	Cross-sectional	2004-2016	Postmenopausal women older than 40 years	> 40 years	1983	Duration and Yes/No	N/A	Hypertension	Adjusted OR = 1.23 (95%CI: 0.81-1.86)	Age, family history, BMI, age of menarche, socioeconomic status, alcohol consumption, and smoking
Ram et al[48] (2008), United Kingdom	Longitudinal observational study	1995–1997	Midlife women transitioning through menopause	46.4 ± 2.7	2516	Yes/No	Not specified.	Hypertension	Adjusted OR = 0.83 (95%CI: 0.68-0.998)	Age, physical activity, daily caloric intake, high school BMI, parity, socioeconomic status, study site, current smoking, and ethnicity
Schwarz et al[46] (2009), United States	Prospective observational study	Began in 1994	Postmenopausal women	Range: 50-79	139681	Duration: No breastfeed, 1-6, 7-12, and 13-23, and ≥ 24 months	Mean = 35 years	Hypertension and diabetes	Hypertension: Adjusted HR = 0.87 (95%CI: 0.82-0.93) for 6 to 12 months’ lactation; Diabetes: Adjusted HR = 0.69 (95%CI: 0.58-0.84) for 6 to 12 months’ lactation	Age, race, parity, age at menopause, education, income, family history (of diabetes mellitus, myocardial infarction or stroke), physical activity, energy, cholesterol, fat, fiber, and sodium intakes, tobacco history, hormone replacement therapy use, aspirin use, and multivitamin use
Stuebe et al[49] (2006), United States	Prospective cohort study	1989-2001	Female registered nurses	Range: 25-55	83585	Duration: No breastfeed, 1-3, > 3-6, > 6-11, > 11-23, 13-23, and > 23 months	1,239,709 person-years of follow-up	Diabetes	Adjusted HR = 0.73 (95%CI: 0.54-0.99) for < 6-month lactation; adjusted HR = 0.62 (95%CI: 0.48-0.81) for 6 to 12 months’ lactation	Age, parity, BMI at 18 years, Dietary score quintile, physical activity, family history of diabetes, smoking status, birth weight of participants, and multivitamin use
Shen et al[50] (2019), China	Prospective observational study	1999-2008	Women diagnosed with GDM	Not specified	1260	Duration	Mean = 3.65 years	Diabetes	Adjusted HR = 0.7 (95%CI: 0.4-1.22) for < 6-month lactation; adjusted HR = 0.34 (95%CI: 0.19-0.6) for 6 to 12 months’ lactation	Pregnant age, education, family income, family history of diabetes, treatment of GDM, smoking, passive smoking, alcohol drinking, leisure-time physical activity, sleeping time, dietary fiber, sweetened beverage drinking, energy intakes of fat, protein, carbohydrate, and prepregnancy, BMI, and 2-hour glucose during pregnancy
Ziegler et al[45] (2012), Germany	Prospective observational study	1989-1999	Women diagnosed with GDM	Not specified	304	Yes/No	From delivery for up to 19 years	Diabetes	Adjusted HR = 0.54 (95%CI: 0.34-0.85)	Diabetes treatment during pregnancy, BMI, and duration of breastfeeding

HR: Hazard ratio; OR: Odds ratio; BMI: Body mass index; DIE: Deep infiltrative endometriosis; GDM: Gestational diabetes mellitus; IVF: In vitro fertilization.