They found that, based on these metabolic levels, women's brains appeared about three years younger, on average, than men's brains of the same chronological age.
The stunning find may explain why girls stay sharper as they get older than boys, scientists said.
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 results were published in the proceedings of the National Academy of Sciences. Our recent multitracer PET brain imaging data demonstrate that as the brain ages, its resting metabolism gradually shifts away from a mixture of nonoxidative and oxidative use of glucose to predominantly oxidative metabolism (4, 5).
More than 200 men and women underwent PET scans, which was then interpreted by an algorithm, as well as data on healthy controls, to determine each individual's age. They found that the algorithm could closely predict a person's chronological age based on their brain's "metabolic age". But she cautions that even though women's brain metabolism is higher overall, some women's brains experience a dramatic metabolic decline around menopause, leaving them vulnerable to Alzheimer's.
This can cause problems later in life and scientists hope to one day slow it down with state-of-the-art drugs or brain therapy.
The researchers also performed the analysis in reverse: They trained the algorithm on women's data and applied it to the men's.
Time wears differently on women's and men's brains.
This relationship continued throughout the adult life span: even among people in their 20s, female brains were more youthful than male brains, suggesting that sex differences during development may set the stage for brain-aging trajectories. Pondering on the reasons why, Goyal said, "It makes us wonder, are hormones involved in brain metabolism and how it ages?" "When we started looking at that, we were pleasantly surprised that when the machine was trying to age a woman compared to a man, it consistently aged the woman to be a little bit younger than the man", Goyal said. "The average difference in calculated brain age between men and women is significant and reproducible, but it is only a fraction of the difference between any two individuals", Goyal said adding that it is stronger than many sex differences that have been reported, but it is nowhere near as big a difference as some sex differences, such as height.
Samuel Neal Lockhart, an assistant professor of gerontology and geriatric medicine at Wake Forest School of Medicine, wrote in an email that the size and scope of this new study is one of its strengths. "Males, their blood flow to the brain decreases quite a bit as they go through puberty".
Still, more research is needed to better understand brain aging overall and to help prevent or delay neurodegenerative diseases, including Alzheimer's, which are "a major growing problem in the United States and elsewhere", he said.
The researchers suspect that women gain this advantage during puberty, Goyal said.
"What we don't know is what it means".
Accordingly, it is important to understand the factors that influence brain aging, particularly in the context of an aging population.