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 (n=262), 1 to less than 6 months (n=210), 6 to less than 10 months (n=169), and 10 months or greater (n=205). 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.
Level of evidence: II.