Why men's brains get slower than women's

Women's brains are four years younger than men's on average

Obviously the exact age can vary from person to person, but to figure out if there are sex differences in that point, the research team conducted positron emission tomography (PET) scans on 205 people - 121 women and 84 men, from 20 to 82 years old.

"Ultimately, many studies keep showing that the differences between any two people tend to be negligible, and that the power of this type of study is in looking at large numbers of brain scans". But if true, the researchers hypothesize that having a metabolically "younger" brain might provide women with "some degree of resilience to aging-related changes" in the brain. This could provide one clue to why women tend to stay mentally sharp longer than men, the authors noted. "Babies and children use some of their brain fuel in a process called aerobic glycolysis that sustains brain development and maturation", said Goyal.

It was already known that men's brains shrink faster with age than women's, but the new results suggest their brain metabolism is different too. The brain still uses sugar for cognitive function, but aerobic glycolysis plateaus at a low level usually by the time people are in their 60s. The findings were published in the journal Proceedings of the National Academy of Science.

Goyal and his colleagues initially set out to see if a computer program could use this brain metabolism pattern to predict someone's age.

They then fed a machine-learning algorithm the male sample data to establish a relationship between age and brain metabolism.

The algorithm yielded brain ages an average of 3.8 years younger than the women's chronological age, according to the study. "We found in fact that females had a younger brain age relative to males". Women consistently fared better.

Then, the researchers flipped their analysis: they trained the algorithm on women's data, and told it to calculate the brain ages for men.

Interestingly, the gap between men and women's brain ages was detectable even in young adults in their 20s. "It is stronger than many sex differences that have been reported, but it's nowhere near as big a difference as some sex differences, such as height". "We're being very cautious in not speculating on what this means in terms of downstream dementia and so forth".

Goyal said that the researchers are now working on another study to test whether the findings play a role in why women don't experience as much cognitive decline as men.

In the next stage of their research, the team will be trying to determine if cognitive problems occur less frequently in people with brains that seem younger. "I think this could mean that the reason women don't experience as much cognitive decline in later years is because their brains are effectively younger, and we are now working on a study to confirm that", he said.



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