The largest study of its kind has uncovered a potential link between the age at which a person starts and stops menstruating and their risk of developing dementia later in life. Analyzing health data from over 270,000 female participants in the United Kingdom Biobank, researchers from University College London (UCL) found that individuals who menstruated for a longer duration, starting later and going through menopause at an older age, had a decreased risk of dementia compared to those with a shorter “reproductive span.”
The study, published in The American Journal of Geriatric Psychiatry, suggests that the duration of exposure to estrogen, the most potent hormone in the estrogen family, may play a protective role in brain aging. Estradiol, the predominant form of estrogen in humans, fluctuates throughout a woman’s life, peaking during reproductive years and declining with menopause. Using menstruation as a proxy for estrogen levels, the researchers found that individuals who started menstruating at age 15 or older had a 12 percent increased risk of dementia, while those who experienced menopause after age 50 had a 24 percent decreased risk.
The protective effect of estrogen on brain health appeared to be independent of hormone replacement therapy, which supplements estrogen after menopause, and was consistent across individuals with and without genetic risk factors for dementia. The findings suggest that estrogen may have a role in mitigating dementia risk, offering a potential explanation for why females are disproportionately affected by the disease compared to males.
However, the study also highlights the complexity of hormone-brain interactions and the need for further research to understand the underlying mechanisms. While animal studies have suggested that estrogen may enhance neural connections and reduce the accumulation of protein plaques associated with Alzheimer’s disease, findings from human studies have been mixed. For instance, some studies have linked longer reproductive spans to larger volumes of gray matter in the brain, while others have found associations between greater sex hormone exposure and accelerated brain aging.
Moreover, the study raises concerns about the impact of reproductive surgeries, such as hysterectomy, on dementia risk. Individuals who underwent reproductive surgery faced an 8 percent increased risk of dementia, particularly if the surgery was performed at a younger age. The abrupt decrease in estrogen exposure following such surgeries may contribute to accelerated changes in the nervous system during the perimenopausal period, increasing the risk of dementia later in life.
The study underscores the importance of prioritizing research on female brain health and the role of sex hormones in cognitive decline. While more research is needed to elucidate the precise mechanisms underlying estrogen’s effects on brain aging and dementia risk, the findings highlight the potential significance of menstrual history as a predictor of cognitive health outcomes. As the population ages and the prevalence of dementia continues to rise, understanding the impact of reproductive factors on brain health will be essential for developing effective prevention and intervention strategies.
