WASHINGTON — A study from Washington University showed that women's brains were about three years younger than men's, offering a clue to why women tend to stay mentally sharp longer than men.

In a study published on Monday in the Proceedings of the National Academy of Sciences, the researchers studied 205 people to figure out how their brains use a portion of sugar in a process called aerobic glycolysis that sustained brain development but dropped steadily with age.

They scanned brains of 121 women and 84 men ranging in age from 20 to 82 years, to measure the flow of oxygen and glucose in their brains and determine the fraction of sugar used to aerobic glycolysis in various regions of the brain.

They employed an artificial intelligence algorithm to find a relationship between age and brain metabolism by feeding it the men's ages and brain metabolism data.

Then, the researchers added 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 age, according to the study.

In reverse, they trained the algorithm on women's data and applied it to men's. The findings are that the men's brains were 2.4 years older than their true ages.

Also, the relative youthfulness of women's brains was detectable even among the youngest participants, who were in their 20s.

"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 the paper's senior author Manu Goyal, an assistant professor of radiology at the university.