Women are far more likely than men to develop Alzheimer’s disease (AD). Traditionally, this disparity has been attributed to women’s longer life expectancy, but emerging research suggests that lifespan alone cannot explain the difference. Scientists have long suspected that variations in how men’s and women’s brains age might hold the key, yet past findings have been inconsistent across brain regions and study methods.
Now, a new study published in the Proceedings of the National Academy of Sciences (PNAS) offers surprising insights. Contrary to common assumptions, the study found that men experience greater age-related decline in several regions of the brain compared to women.
Men Show Greater Brain Decline with Age
Researchers analyzed 12,638 brain MRIs from 4,726 cognitively healthy participants aged 17 to 95, each with at least two scans. The aim was to map how aging affects brain structure and to determine whether the patterns differ by sex.
The results revealed that men experienced more widespread declines in cortical thickness, surface area, and subcortical structures as they aged. In contrast, women showed significant decline in only a few regions, although they exhibited more ventricular expansion in older adulthood—a marker of brain volume loss.
These findings suggest that while sex-based differences in brain aging are real, they may not directly explain why women are diagnosed with Alzheimer’s more often.
Beyond Brain Atrophy: Searching for the Real Cause
“The higher prevalence of AD diagnoses in women likely stems from factors beyond differential rates of age-related brain atrophy,” the study authors wrote.
Researchers point to several other possible contributors. Genetics may play a crucial role—particularly the APOE ε4 allele, which is known to influence protein accumulation in the brain and may act differently in men and women. Additionally, hormonal changes, diagnostic biases, and sociocultural factors could all contribute to women’s higher Alzheimer’s rates.
The Role of Life Expectancy and Bias
The study also considered the impact of survival bias. Because women generally live longer, men who die earlier may not reach the ages when Alzheimer’s typically develops, skewing apparent prevalence rates.
Furthermore, the study participants were, on average, more educated, a known protective factor against Alzheimer’s. This creates a representativity bias, as the sample may not accurately reflect the broader population.
When researchers adjusted for life expectancy, some patterns shifted. Certain brain declines in men disappeared, while new areas of decline appeared in women, particularly in the hippocampus, a region critical for memory.
A Complex Picture of Brain Aging
“The interpretation of these sex differences is complicated by our life expectancy analyses,” the authors explained. “Removing proximity-to-death effects eliminated some cortical declines in men but revealed greater hippocampal decline in women. Whether this represents biological aging differences or artifacts remains uncertain.”
As reported by medicalxpress, the team cautioned that these results should be interpreted carefully, given the potential health and sampling biases in their dataset.
Moving Closer to Understanding Alzheimer’s Mechanisms
Although the study raises new questions, it also brings researchers a step closer to understanding how age, sex, and brain biology interact in the development of Alzheimer’s disease. By identifying where and how male and female brains differ in the aging process, scientists can refine their investigations into genetic, hormonal, and environmental factors that influence dementia risk.
Ultimately, this research highlights that Alzheimer’s is not just a disease of aging—but of complex biological differences that continue to unfold as science advances.