OBJECTIVE: To examine dose–response relationships between the cumulative number of months women lactated and postmenopausal risk factors for cardiovascular disease.
METHODS: We examined data from 139,681 postmenopausal women (median age 63 years) who reported at least one live birth on enrolling in the Women’s Health Initiative observational study or controlled trials. Multivariable models were used to control for sociodemographic (age, parity, race, education, income, age at menopause), lifestyle, and family history variables when examining the effect of duration of lactation on risk factors for cardiovascular disease, including obesity (body mass index [BMI] at or above 30), hypertension, self-reported diabetes, hyperlipidemia, and prevalent and incident cardiovascular disease.
RESULTS: Dose-response relationships were seen; in fully adjusted models, women who reported a lifetime history of more than 12 months of lactation were less likely to have hypertension (odds ratio [OR] 0.88, P<.001), diabetes (OR 0.80, P<.001), hyperlipidemia (OR 0.81, P<.001), or cardiovascular disease (OR 0.91, P=.008) than women who never breast-fed, but they were not less likely to be obese. In models adjusted for all above variables and BMI, similar relationships were seen. Using multivariate adjusted prevalence ratios from generalized linear models, we estimate that among parous women who did not breast-feed compared with those who breast-fed for more than 12 months, 42.1% versus 38.6% would have hypertension, 5.3% versus 4.3% would have diabetes, 14.8% versus 12.3% would have hyperlipidemia, and 9.9% versus 9.1% would have developed cardiovascular disease when postmenopausal. Over an average of 7.9 years of postmenopausal participation in the Women’s Health Initiative, women with a single live birth who breast-fed for 7–12 months were significantly less likely to develop cardiovascular disease (hazard ratio 0.72, 95% confidence interval 0.53–0.97) than women who never breast-fed.
CONCLUSION: Among postmenopausal women, increased duration of lactation was associated with a lower prevalence of hypertension, diabetes, hyperlipidemia, and cardiovascular disease.
LEVEL OF EVIDENCE: II
Lactation may decrease women’s risk of cardiovascular disease after menopause.
From the 1Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania; the 2Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington; the 3Division of Maternal-Fetal Medicine, University of North Carolina School of Medicine, Chapel Hill, North Carolina; the 4University of California, San Diego, La Jolla, California; and the 5Department of Epidemiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania.
See related editorial on page 972.
The Women’s Health Initiative program is funded by the National Heart, Lung, and Blood Institute, National Institutes of Health, U.S. Department of Health and Human Services, through contracts N01WH22110, 24152, 32100-2, 32105-6, 32108-9, 32111-13, 32115, 32118-32119, 32122, 42107-26, 42129-32, and 44221. Dr. Schwarz is funded by the Eunice Kennedy Shriver National Institute of Child Health and Development, K23 HD051585.
Corresponding author: Eleanor Bimla Schwarz, MD, MS, Assistant Professor of Medicine, Epidemiology, Obstetrics, Gynecology, and Reproductive Sciences, University of Pittsburgh, Center for Research on Health Care, 230 McKee Place, Suite 600, Pittsburgh, PA 15213; e-mail: Schwarzeb@upmc.edu.
Financial Disclosure The authors did not report any potential conflicts of interest.