Does long-term lactation protect premenopausal women against hypertension risk? a Korean womenʹs cohort study

Background Little is known about the long-term effect of lactation on maternal cardiovascular health except for a few animal or human experimental studies. The objective of this study was to examine the effects of lactation on the incidence of hypertension in premenopausal women. Methods The data were derived from a cohort study with 6 years follow-up (1995–2000). The cohort was composed of 177,749 Korean premenopausal women, aged 20–59, who had medical evaluations in 1992 and 1994. During the follow-up, blood pressure was measured as part of the 1996, 1998, and 2000 periodic examinations. Results In multivariate Cox proportional hazard models, lactation decreased the risk of hypertension (risk ratio, 0.92; 95% confidence interval, 0.90–0.96). Compared with women who with no history of lactation, 1–6 months of lactation decreased the risk of hypertension (RR, 0.90; 95% CI, 0.87–0.93), as did 7–12 months (RR, 0.92; 95% CI, 0.87–0.98) or 13–18 months (RR, 0.93; 95% CI, 0.86–0.99). In particular, the coexistence of obesity and no lactation increased the risk of hypertension (P for interaction = 0.028). Conclusion This finding suggests that lactation may be a protective factor against hypertension among premenopausal women.