Duration of lactation and incidence of myocardial infarction in middle to late adulthood.

OBJECTIVE We assessed the relation between duration of lactation and maternal incident myocardial infarction. STUDY DESIGN This was a prospective cohort study of 89,326 parous women in the Nurses' Health Study. RESULTS During 1,350,965 person-years of follow-up, 2540 cases of coronary heart disease were diagnosed. Compared with parous women who had never breastfed, women who had breastfed for a lifetime total of 2 years or longer had 37% lower risk of coronary heart disease (95% confidence interval, 23-49%; P for trend < .001), adjusting for age, parity, and stillbirth history. With additional adjustment for early-adult adiposity, parental history, and lifestyle factors, women who had breastfed for a lifetime total of 2 years or longer had a 23% lower risk of coronary heart disease (95% confidence interval, 6-38%; P for trend = .02) than women who had never breastfed. CONCLUSION In a large, prospective cohort, long duration of lactation was associated with a reduced risk of coronary heart disease.