Lactation Duration and Midlife Atherosclerosis

OBJECTIVE: To evaluate lactation duration in relation to subsequent atherosclerosis in women during midlife. METHODS: The Coronary Artery Risk Development in Young Adults study is a multicenter prospective cohort that enrolled 2,787 women in 1985-1986 (ages 18-30 years, 52% black, 48% white), of whom 2,014 (72%) attended the 20-year follow-up examination in 2005-2006. We selected 846 women (46% black) without heart disease or diabetes at baseline who delivered one or more times after the baseline evaluation, had cardiometabolic risk factors measured at baseline, and had maximum common carotid intima-media thickness (mm) measured at the 20-year follow-up examination in 2005-2006. Lactation duration was summed across all postbaseline births for each woman and (n, women) categorized as: 0 to less than 1 month (n262), 1 to less than 6 months (n210), 6 to less than 10 months (n169), and 10 months or greater (n205). Multiple linear regression models estimated mean common carotid intima-media thickness (95% confidence interval) and mean differences among lactation duration groups compared with the 0 to less than 1-month group adjusted for prepregnancy obesity, cardiometabolic status, parity, and other risk factors. RESULTS: Lactation duration had a graded inverse association with common carotid intima-media thickness; mean differences between 10 months or greater compared with 0 to less than 1 month ranged from -0.062 mm for unadjusted models (P trend <.001) to -0.029 mm for models fully adjusted for prepregnancy body mass index (BMI) and cardiometabolic risk factors, parity, smoking, and sociodemographics (P trend.010). Stepwise addition of potential mediators (BMI, systolic blood pressure at the 20-year follow-up examination) modestly attenuated the lactation and common carotid intima-media thickness association to -0.027 and -0.023 mm (P trend.019 and.054). CONCLUSION: Shorter lactation duration is associated with subclinical atherosclerosis independent of prepregnancy cardiometabolic risk factors and traditional risk factors. The magnitude of differences in carotid artery intima-media thickness may represent greater vascular aging. Lactation may have long-term benefits that lower cardiovascular disease risk in women.