Postmenopausal women who breastfed their children had a lower risk of stroke compared with women who had children but never breastfed, with non-Hispanic black women showing a significantly stronger association between breastfeeding and lower stroke risk, according to results from the prospective Women’s Health Initiative Observational Study.
“Some studies have reported that breastfeeding may reduce the rates of breast cancer, ovarian cancer and risk of developing type 2 diabetes in mothers. Recent findings point to the benefits of breastfeeding on heart disease and other specific cardiovascular risk factors,” Lisette T. Jacobson, PhD, of the department of preventive medicine and public health at the University of Kansas, Wichita, said in a statement.
Dr. Jacobson and her colleagues evaluated 80,191 women from the Women’s Health Initiative (WHI) Observational Study who were aged 50-79 at baseline. The average age was 64 years, and 83% were white, 8% were non-Hispanic black, 4% were Hispanic, and 5% were another race or ethnicity. Of the women observed, 58% had breastfed and 3.4% had a stroke within an average of 13 years of follow-up. The investigators used three adjusted regression models to analyze stroke risk: Model 1 was minimally adjusted, model 2 was adjusted for nonmodifiable potential confounders, and model 3 was adjusted for modifiable lifestyle factors.
There was a 23% lower risk of stroke among all postmenopausal women who breastfed compared with those who never breastfed, with women who breastfed between 1 month and 6 months carrying a 19% lower risk of stroke. In the minimally adjusted model, non-Hispanic white women who breastfed carried a 21% lower risk, Hispanic women had an adjusted 32% lower risk, and women of other races and ethnicity had a 24% lower risk of stroke. However, women who were non-Hispanic black had a stronger association with breastfeeding and stroke reduction, with a 48% lower risk, and non-Hispanic white and non-Hispanic black women showed a stronger association between longer duration of breastfeeding and lower stroke risk when results were minimally adjusted, the investigators said. All differences were statistically significant.
The investigators noted the study’s observational nature and said they were not able to determine what caused breastfeeding’s association with lower stroke risk, with other factors potentially affecting results.
“Breastfeeding is only one of many factors that could potentially protect against stroke,” Dr. Jacobson said in the report,online in the Journal of the American Heart Association. “Others include getting adequate exercise, choosing healthy foods, not smoking, and seeking treatment if needed to keep your blood pressure, cholesterol, and blood sugar in the normal range.”
They also noted potential limitations in the study: the WHI cohort’s low number of strokes in follow-up, lack of classification of stroke, recall bias due to the women self-reporting strokes, average age at baseline, and lack of data on pregnancy.
“Our study did not address whether racial/ethnic differences in breastfeeding contribute to disparities in stroke risk,” Dr. Jacobson said. “Additional research should consider the degree to which breastfeeding might alter racial/ethnic differences in stroke risk.”
“This is an observational, prospective cohort study that was performed very carefully, but it is important to not conclude causality in that breastfeeding results in a reduction in late life stroke,” Larry B. Goldstein, MD, said in an email interview.
Dr. Goldstein, a neurologist who has published several guidelines on primary prevention and early management of stroke with the American Heart Association, noted that although the authors addressed many confounders, studies of this type are still open to residual confounding. He said one of the factors the authors could not measure was eclampsia and preeclampsia, which inhibits breastfeeding.
“The possibility of unmeasured confounding despite how well the study was done is still there. But having said that, the recommendations for breastfeeding are strong from the American Academy of Pediatrics and from the World Health Organization,” and other studies have found an association with a reduction in later life cardiovascular disease, said Dr. Goldstein, the Ruth L. Works professor and chairman in the department of neurology at the University of Kentucky, Lexington. “But just in terms of the benefits to the mother and to the child from breastfeeding, this is another potential plus [in that] even if it doesn’t pan out, it doesn’t really change the recommendation for breastfeeding.”
Dr. Goldstein noted that finding these results in a different prospective cohort would strengthen the recommendations, as would examining whether factors such as lifestyle affected stroke risk for women.
“Showing causality is always going to be difficult,” he stressed. “There is no particular causal mechanism that’s been espoused for how this might decrease stroke risk in later life.”
This study is funded by Frontiers: The Heartland Institute for Clinical and Translational Research and the Wichita Center for Graduate Medical Education–Kansas Bioscience Authority. The WHI program is funded by the National Heart, Lung, and Blood Institute, the National Institutes of Health, and the U.S. Department of Health and Human Services. The authors reported having no conflicts of interest.
SOURCE: Jacobson LT et al. J Am Heart Assoc. 2018 Aug 22. .