Abstract
BACKGROUND: Although lactation may reduce maternal risk of breast cancer, other potential long-term health benefits of lactation for mothers are largely unknown. OBJECTIVES: We examined whether the durations of predominant and any lactation were associated with maternal risks of coronary artery disease (CAD) and stroke. METHODS: In this prospective cohort study, we followed up 6857 mothers from the Copenhagen Perinatal Cohort who gave birth during 1959-1961 at median age 24 y (IQR, 20-30 y). Durations of predominant and any lactation were assessed at the infant's 1-y examination. Diagnoses of CAD (n = 701 at 45-70 y; n = 593 at >70 y) and stroke (n = 410 at 45-70 y; n = 535 at >70 y) were obtained from national health registers during 1977-2022. Hazard ratios (HRs) and 95% CIs were estimated by Cox regressions without and with adjustment for demographics, metabolic risk during pregnancy, pregnancy complications, and reproductive history. RESULTS: Durations of predominant and any lactation were inversely associated with risk of CAD, but not with stroke, when using lactation as a continuous variable. In categorical analyses, mothers who lactated for >4 months had 41% (HR: 0.59; 95% CI: 0.46, 0.75) and 34% (HR: 0.66; 95% CI: 0.48, 0.92) lower risk of CAD and stroke, respectively, at ages 45-70 y, compared with mothers who lactated ≤0.5 months. After adjustment for demographic, metabolic, and reproductive risk factors during pregnancy, these associations attenuated (HR: 0.78; 95% CI: 0.60, 1.01 for CAD; HR: 0.90; 95% CI: 0.64, 1.27 for stroke). No associations were observed with CAD or stroke diagnosed after age 70 y. CONCLUSIONS: Limited evidence exists for an association between lactation and maternal risk of stroke. Longer durations of lactation are associated with lower risks of maternal CAD diagnosed before age 70 y. Adjustment for risk factors attenuate the associations, which suggests these factors may partly confound the benefits of lactation on maternal risks of CAD.