Pregnancy, breastfeeding associated with higher levels of cognitive function for postmenopausal women

Female brains have historically evolved to adapt to pregnancy, undergoing structural and functional changes. But the cognitive health implications of these adaptations have long been overlooked - until now.

A new study led by UCLA anthropology professor Molly Fox has found that pregnancy and breastfeeding are linked with stronger long-term cognitive ability in postmenopausal women. Published this month in the scientific journal Alzheimer's & Dementia, the study found that an increase in cumulative time spent pregnant and time spent breastfeeding correlated with greater cognition, verbal memory and visual memory later in life.

Researchers used data from the Women's Health Initiative Memory Study and the Women's Health Initiative Study of Cognitive Aging, which annually assessed more than 7,000 women aged about 70 for up to 13 years.

Women are disproportionately affected by Alzheimer's disease, something that has not been fully explained by the length of life span. Fox's study aimed to address this question by examining the relationship between reproductive histories and cognitive function in a large group over a long period, something previous studies had not yet accomplished.

"Any ways in which we can focus public health outreach or clinical interventions toward higher-risk populations leads to more effective and efficient efforts," Fox said.

As the team began their research, they hypothesized that longer breastfeeding, more pregnancies, and a greater ratio of the two would correspond with better cognitive function in postmenopausal women. The results matched the theory: Researchers found that women who were pregnant for an average of 30.5 months, compared with those who had never been pregnant, were expected to have a 0.31% higher global cognition score. A woman who breastfed for an average of 11.6 months in their lifetime would be expected to have a 0.12% higher global cognition score if everything else were held equal.

The results indicated that each additional month of pregnancy was associated with a 0.01-point higher overall cognitive ability score. Each additional month of breastfeeding demonstrated the same increase, as well as a 0.02-point higher verbal and visual memory score. While these effect sizes are small, they are comparable to what has been observed for other known protective factors like non-smoking and high physical activity. With a disease like Alzheimer's that has been so elusive to prevention and treatment successes, and is so prevalent, even small changes to a person's risk are exciting discoveries.

This study adds to our general understanding of how pregnancy and breastfeeding relate to women's brain health over time. In the short-term, many women experience a postpartum decline in memory and cognitive function - often dubbed "mommy brain" - which is most noticeable in the months after childbirth. But long-term, pregnancy may be associated with improved cognitive health, indicating a shift from the initial and temporary postpartum decline.

The findings revealed that women who had been pregnant had 0.60-point higher cognitive ability scores compared to women who had never been pregnant. Similarly, women who breastfed had 0.19-point higher scores and 0.27-point higher verbal memory scores compared to those who never breastfed.

While these results support a connection between pregnancy and breastfeeding with long-term brain resilience, questions remain about the biological and sociocultural processes behind this relationship. The researchers wrote in the study that "more adult children could be a factor in the increased cognitive health, as supportive relationships could possibly buffer stress, promote well-being or encourage healthy behavior."

The study team is next working to identify which mechanisms link reproductive histories to cognitive resilience. They believe that such information could identify new therapeutic opportunities that "replicate or enhance the protective effects observed in women with specific reproductive histories," they wrote.

"If we can figure out, as a next step, why those reproductive patterns lead to better cognitive outcomes in old age, then we can work toward figuring out how to craft therapies - for example, new drugs, repurposed drugs or social programs - that mimic the naturally-occurring effect we observed," Fox said.

The team's research may open the door to potential advancements in preventative strategies targeting women at greater risk of Alzheimer's disease. At the population level, understanding this pattern may encourage further research into how changing fertility behaviors will affect trends in brain aging.

Studies like the one led by Fox highlight the growing evidence that pregnancy and breastfeeding may play a role in brain function, with implications for women's health across generations.

Data from the Women's Health Initiative Memory Study and the Women's Health Initiative Study of Cognitive Aging were used to support these findings. Postmenopausal women participated in reproductive history interviews, annual global cognitive assessments and multi-domain cognitive testing.

This research was performed by the Women's Health Initiative and was funded in part by the National Heart, Lung and Blood Institute under the National Institutes of Health. Fox was supported by the National Institute on Aging at the National Institutes of Health.