Breastfeeding History Linked to Reduced Stroke Risk

Postmenopausal women who report ever having breastfed have a 23% reduced risk for stroke later in life compared with those who had children but never breastfed, a new observational study suggests.

For non-Hispanic black women, that risk is as much as 48% lower after adjustment for other stroke risk factors, the researchers note.

"This study provides data to inform programs that aim to reduce stroke risk factors by promoting healthy behaviors, including culturally sensitive breastfeeding support among populations that unduly carry the largest burden of stroke," first author, Lisette T. Jacobson, PhD, assistant professor in the Department of Preventive Medicine and Public Health at the University of Kansas School of Medicine-Wichita, told Medscape Medical News.

"In fact, our study results suggest that non-Hispanic black women may especially benefit from longer breastfeeding duration as one of many factors to help guard against stroke."

The findings are from a study published online August 22 in the Journal of the American Heart Association.

Women's Health Initiative

Previous studies looking at the potential protective effect of breastfeeding on the mother have focused largely on cardiovascular risk factors, showing nine or more cumulative months of breastfeeding to be associated with a reduced risk for hypertension, hyperlipidemia, and metabolic syndrome, the authors write. Prolonged breastfeeding is also linked to reductions in the risk for type 2 diabetes and lower maternal postpartum weight.

Few studies, however, have looked specifically at the risk for stroke, they note. "This is among the first studies to examine breastfeeding and a possible relationship to stroke risk for mothers, as well as how such a relationship might vary by ethnicity."

The analysis included 80,191 women who participated in the Women's Health Initiative observational study and had delivered at least one child.

Of these, 2699 (3.4%) experienced a stroke during a follow-up period of 12.6 years. With an average age at baseline of 63.7 years, 58% (n = 46,699) of women reported having ever breastfed, with 51% breastfeeding for 1 to 6 months, 22% for 7 to 12 months, and 27% for 13 or more months.

After adjustment for multiple risk factors, women who had breastfed had a significant reduction in the risk for stroke (adjusted hazard ratio [HR], 0.77; 95% confidence interval [CI], 0.70 - 0.83), with the strongest association seen among non-Hispanic black women (adjusted HR, 0.52; 95% CI, 0.37 - 0.71).

The risk reduction among Hispanic women was 32% (HR, 0.68; 95% CI, 0.30 - 1.54) compared with those who did not breastfeed and 21% (HR, 0.79; 95% CI, 0.73 - 0.87) in non-Hispanic white women.

A longer duration of breastfeeding was also associated with a significant stroke risk reduction. For those who breastfed 1 to 6 months, the stroke reduction was 19% compared with those who never breastfed (HR, 0.81; 95% CI, 0.74 - 0.90), while the reduction was 25% with breastfeeding of 7 to 12 months (HR, 0.75; 95% CI, 0.66 - 0.85) and 26% for 13 months or more (HR, 0.74; 95% CI, 0.65 - 0.83).

The protective effect of longer breastfeeding appeared to be stronger in non-Hispanic white women and in non-Hispanic black women (trend P < .01).

The reductions were seen after adjustment for such factors as age, race/ethnicity, education, number of children, family history, exercise at baseline, smoking, body mass index (BMI), and multivitamin use at baseline.

Jacobson noted that the greater risk observed in non-Hispanic black women is consistent with a higher risk for stroke, in general, among those women.

"It was not surprising to see greater risk reduction among non-Hispanic black women as this population unduly carries the largest burden of stroke and along with Hispanic women, have increased rates of hypertension, obesity, diabetes, and physical inactivity, which are also stroke risk factors," she said.

The findings are concerning, however, in light of evidence showing those who appear to benefit the most, the non-Hispanic black women, in fact breastfeed the least.

Studies have shown that only 35% of non-Hispanic black women breastfeed at 6 months and just 17% do so at 12 months postpartum.

The corresponding rates for Hispanic women are only slightly higher, with 51% breastfeeding at 6 months and 26% at 12 months postpartum, compared with rates in non-Hispanic white women of 56% at 6 months and 31% at 12 months.

The American Academy of Pediatrics and World Health Organization (WHO) meanwhile each recommend exclusive breastfeeding for 6 months and continued breastfeeding for 1 year or longer, citing an expansive multitude of health benefits to the mother and child.

Known Benefits Extensive

The authors underscore that the study results do not necessarily establish a causal relationship between breastfeeding and the risk for stroke. Breastfeeding in general is known to be linked to healthier lifestyles, and the authors note that in the study, women who never breastfed indeed had higher rates of smoking, higher BMI, less exercise, and reduced healthy food consumption.

"Study findings could partially be explained by the fact that breastfeeding women tend to live healthier lives than non-breastfeeding women, indicating that breastfeeding is more of a risk marker than risk factor."

The fact that the association remained statistically significant even after adjustment for known risk nevertheless suggests the need for more longitudinal data to better understand possible biological mechanisms linking breastfeeding and a reduction in stroke risk, Jacobson said.

"This is certainly a possibility, though we really need biochemical measurements longitudinally to corroborate epidemiologic findings that human lactation positively influences origins of disease," she explained.

"I am not familiar with any notable theories on biological mechanisms that could explain risk reduction for this population. This warrants further investigation for future research.'

Other notable limitations include the relatively small number of strokes in the study and the exclusion of women in the Women's Health Initiative who experienced severe strokes prior to recruitment in the study.

The findings nevertheless contribute potentially important information in assessing patients' stroke risk, Jacobson said.

"The knowledge that a patient breastfed her children and the total number of months of breastfeeding across all children she had will help healthcare providers in assessing a patient's risk profile for stroke."

"What we can do today is to design and implement culturally informed programs that mitigate stroke risk and promote healthy behaviors, including breastfeeding support, among populations that carry the largest health burden of stroke."

Risk Marker or Factor?

Commenting on the findings for Medscape Medical News, Larry B. Goldstein, MD, chairman of the Department of Neurology and co-director of the Kentucky Neuroscience Institute - KY Clinic at the University of Kentucky in Lexington, agreed with the suggestion that breastfeeding, or failure to breastfeed, may have more of a role as a risk marker than a risk factor.

"Reports of studies using this type of design are at risk for a variety of biases and unmeasured confounding," he said in an interview. "Even if a statistical relationship does exist in adjusted analyses, [it] cannot distinguish between a risk marker, which does not directly lead to disease, and a risk factor, which is directly linked to disease."

Nevertheless, "this is a well-conducted analysis of data from a prospective cohort study," Goldstein added, underscoring the need to encourage breastfeeding.

"There are a large variety of benefits of breastfeeding for the child and likely for the mother, supporting evidence-based guidelines from the American Academy of Pediatrics and the WHO," he said.

"Although it is premature to conclude that breastfeeding directly leads to a reduction in later-life stroke risk, this study should not dissuade women from breastfeeding, and if anything, further encourage them to do so."

The study was 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, National Institutes of Health, US Department of Health and Human Services. The authors and Goldstein have disclosed no relevant financial relationships.

J Am Heart Assoc. Published August 22, 2018. Full text

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