Women’s brains are almost four years younger than men’s, of the same chronological age, a new study from Washington University has found.
The human brain tends to shrink with age. Metabolism also slows as people grow older, but men’s brain diminishes faster than women’s.
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The study finds the difference is apparent from early adulthood and remains into old age. The findings could be one clue to why women tend to stay mentally sharp longer than men.
“We’re just starting to understand how various sex-related factors might affect the trajectory of brain aging and how that might influence the vulnerability of the brain to neurodegenerative diseases,” said senior author Manu Goyal, MD, an assistant professor of radiology at the university’s Mallinckrodt. “Brain metabolism might help us understand some of the differences we see between men and women as they age.”
The brain runs on sugar, but researchers have understood little about how brain metabolism differs between men and women. And how the brain uses sugar changes as people grow and age.
The study included 205 people – 121 women and 84 men – from 20 years of age to 82.
Participant underwent PET scans to measure the flow of oxygen and glucose in their brains. For each one, the researchers trained a machine-learning algorithm to find a relationship between age and brain metabolism by feeding it the men’s ages and brain metabolism data.
Then, the researchers entered women’s brain metabolism data into the algorithm and directed the program to calculate each woman’s brain age from its metabolism. The algorithm yielded brain ages an average of 3.8 years younger than the women’s chronological ages.
In the next step, the researchers performed the analysis in reverse: They trained the algorithm on women’s data and applied it to men’s. This time, it was found that men’s brains were 2.4 years older than their true ages.
The relative youthfulness of women’s brains was detectable even among the youngest participants, who were in their 20s.
“It’s not that men’s brains age faster – they start adulthood about three years older than women, and that persists throughout life,” said Goyal, who is also an assistant professor of neurology and of neuroscience. “What we don’t know is what it means. I think this could mean that the reason women don’t experience as much cognitive decline in later years is that their brains are effectively younger, and we’re currently working on a study to confirm that.”
Older women tend to score better than men of the same age on tests of reason, memory and problem-solving.
The study is reported in Proceedings of the National Academy of Sciences.