October 15, 2025
3 minute read
The male brain contracts faster than the female brain. What does this mean for Alzheimer's disease?
Women's brains age more slowly than men's, but they still have higher rates of Alzheimer's disease.
Healthy brain(left) and brains affected by Alzheimer's disease.
TheVisualMD/Scientific source
According to a longitudinal study published today in the journal Proceedings of the National Academy of Sciences. The authors suggest this means that age-related brain changes do not explain why women are more likely to be diagnosed with Alzheimer's disease than men.
“It's important to understand what happens in the healthy brain so we can better understand what happens when people get neurodegenerative diseases,” says Fiona Kumfor, a clinical neuropsychologist at the University of Sydney, Australia. This study expands scientists' understanding of typical brain aging, she adds.
Alzheimer's disease is diagnosed almost twice as often in women than men, and aging is the biggest risk factor for developing the disease. This has prompted research into age-related sex differences in the brain. “If women's brains had deteriorated more, this could help explain their higher prevalence of Alzheimer's disease,” says co-author Ann Ravndal, a graduate student at the University of Oslo.
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Previous studies examining sex differences in brain aging have shown mixed results, Ravndal adds. Several studies have shown that men experience greater loss of total gray matter and hippocampal size compared to women, while other studies report more dramatic gray matter loss in women.
Brain scan
The latest study included more than 12,500 magnetic resonance imaging (MRI) brain scans of 4,726 people (at least two scans per person, taken an average of three years apart) who did not have Alzheimer's disease or any cognitive impairment and were controls in 14 larger data sets. The researchers compared how people's brain structures changed over time, looking at factors such as gray matter thickness and the size of areas associated with Alzheimer's disease, such as the hippocampus, which is important for memory.
Overall, men showed greater volume loss in more brain regions than women. For example, the postcentral cortex, which is responsible for processing sensations of touch, pain and temperature, as well as body position and movement, shrank by 2.0% per year in men and 1.2% per year in women.
Kumfor says the results show that men age faster than women. Men also have a shorter life expectancy.
If these changes did play a role in the development of Alzheimer's disease, the study would show that women had greater declines in activity in areas associated with the disease, such as the hippocampus and precuneus, which are involved in memory, says Amy Brodtmann, a physician researcher in cognitive health at Monash University in Melbourne, Australia.
Ravndal says the results point to other possible explanations for sex differences in the prevalence of Alzheimer's disease, such as differences in survival or susceptibility to the disease.
That sex differences in brain volume do not appear to play a role in the disease is not surprising, says Kumfor, since neurodegenerative conditions are complex. Understanding these disorders will require longitudinal studies of people with Alzheimer's disease to compare how their brains change over time. “Simply looking at age-related changes in brain atrophy is unlikely to explain the complexities behind it,” she adds.
Complex disease
While the study is robust, further research with more diverse data sets is needed, Brodtmann says. For example, the people included in the study had a high level of education (a protective factor against Alzheimer's disease), meaning they were not fully representative of the general population. The datasets also lacked information on other factors that influence a person's risk of developing Alzheimer's disease, such as ethnicity and the age at which women reach menopause.
The authors say that when they adjusted their analysis for educational level, some parts of men's brains no longer showed steeper declines than women's. When they compared men and women predicted to live the same number of years rather than men the same age, both groups' brains deteriorated at the same rate.
This article is reproduced with permission and has been first published October 13, 2025.
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