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Study Identifies Associations Between Reproductive History and Cognitive Function in Postmenopausal Women

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Pregnancy and Breastfeeding Linked to Higher Cognitive Scores in Postmenopausal Women

A recent study, published in the scientific journal Alzheimer's & Dementia, suggests an association between cumulative time spent pregnant and breastfeeding and higher cognitive scores in postmenopausal women. The research, which analyzed data from over 7,000 participants, indicates that while these observed differences are modest, they are statistically significant.

The research, which analyzed data from over 7,000 participants, suggests that while these observed differences are modest, they are statistically significant.

Background

Female mammals, including humans, undergo structural and functional brain changes during pregnancy and lactation. The long-term effects of these changes on neurodegenerative disease risk or cognitive resilience have been a subject of investigation with mixed findings in previous studies. While some reports suggest superior cognitive performance in postmenopausal women who breastfed, others have indicated potential detrimental cognitive effects.

This study aimed to examine the relationship between reproductive histories and cognitive function over a long period, particularly addressing the disproportionate effect of Alzheimer's disease on women.

Study Design and Methodology

Led by UCLA anthropology professor Molly Fox, the study utilized data from two longitudinal observational cohorts: the Women's Health Initiative Memory Study (WHIMS) and the Women's Health Initiative Study of Cognitive Aging (WHISCA).

Participants

The analysis included 6,083 participants from WHIMS and 1,935 from WHISCA. These were dementia-free postmenopausal women, aged 65 to 79 years for WHIMS and 66 to 84 years for WHISCA, at baseline. Participants with fewer than two cognitive assessments or who developed dementia within one year of baseline were excluded. The majority of participants were White and U.S.-based.

Data Collection

Reproductive history data was collected via retrospective baseline interviews, including total cumulative lifetime months pregnant (including non-livebirths) and total cumulative months breastfeeding. Secondary exposures included the breastfeeding-to-pregnancy ratio (BF:PREG), gravidity (number of pregnancies), and breastfeeding history.

Cognitive Assessments

Cognitive outcomes were assessed annually for up to 13 years (10.4 years for WHIMS and 8.4 years for WHISCA). These included:

  • Global cognition (modified Mini-Mental State Examination)
  • Verbal memory (California Verbal Learning Test)
  • Visual memory (Benton Visual Retention Test)

Statistical Analysis

Linear mixed-effects models were employed, adjusted for factors such as age, education, race, income, apolipoprotein E ε4 status, and estrogen therapy.

Key Findings

The study found associations between greater numbers of pregnancies, longer breastfeeding durations, and higher BF:PREG ratios with better global cognitive performance in postmenopausal women.

The study found associations between greater numbers of pregnancies, longer breastfeeding durations, and higher BF:PREG ratios with better global cognitive performance in postmenopausal women.

Impact of Pregnancy

  • Each additional month of pregnancy was associated with a 0.01-point increase in global cognition scores in fully adjusted models.
  • Women who had been pregnant showed a 0.60-point higher global cognition score compared to those who had never been pregnant.
  • Total time pregnant was not significantly associated with visual or verbal memory scores.

Impact of Breastfeeding

  • Each additional month of breastfeeding was associated with a 0.01- to 0.02-point increase in global cognition, visual memory, and verbal memory scores.
  • Participants who breastfed for at least one month exhibited 0.19-point higher global cognition scores and 0.27-point higher verbal memory scores compared to those who never breastfed. Associations with visual memory were not statistically significant in this comparison.

Breastfeeding-to-Pregnancy Ratio (BF:PREG)

  • Each unit increase in the BF:PREG ratio was associated with 0.24-point higher global cognition, 0.38-point higher visual memory, and 0.54-point higher verbal memory scores.

Effect Sizes Noted

While the observed associations were statistically significant, the effect sizes were characterized as modest. Researchers noted that these effect sizes are comparable to those observed for other known protective factors against cognitive decline, such as non-smoking and high physical activity.

Interpretations and Limitations

The study's authors suggest that while many women experience a short-term postpartum decline in memory and cognitive function, these findings indicate that, long-term, pregnancy and breastfeeding may be associated with improved cognitive health. However, the study's observational design means the findings should not be interpreted as causal.

While many women experience a short-term postpartum decline in memory and cognitive function, these findings indicate that, long-term, pregnancy and breastfeeding may be associated with improved cognitive health.

Limitations highlighted by the researchers include:

  • Potential for residual confounding (unaccounted factors influencing the results).
  • Possibility of reverse causation (where healthier cognition might influence reproductive choices).
  • The predominantly White, U.S.-based cohort, which limits the generalizability of the findings to other populations.
  • Uncertainty regarding the clinical significance of these modest differences in cognitive scores.
  • The study's results do not provide a basis for informing reproductive decision-making.

Future Research

The biological and sociocultural processes underlying the observed relationships are not yet fully understood. Researchers plan to identify the specific mechanisms linking reproductive histories to cognitive resilience, noting that factors like supportive relationships from adult children could potentially contribute to increased cognitive health.

This information could potentially lead to new therapeutic opportunities that replicate or enhance the protective effects observed, and may contribute to advancements in preventative strategies for women at a greater risk of Alzheimer's disease.

The research was performed by the Women's Health Initiative and funded in part by the National Heart, Lung and Blood Institute under the National Institutes of Health, with additional support from the National Institute on Aging at the National Institutes of Health.