Scientists have found an odd difference between the brains of men and women. Women’s brains appear younger than their age, but men’s brains appear to be older.
When looking at the brains of both sexes of the same chronological age, women’s brains were 3.8 years younger and men’s brains were 2.4 years older on average. The finding, published online in the Proceedings of the National Academies of Science, may explain why older women tend to outperform their male peers on reason, memory, and problem-solving tests.
“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, a researcher Washington University in St. Louis, in a statement. “Brain metabolism might help us understand some of the differences we see between men and women as they age.”
Our brains rely on sugar as their principal form of fuel. But how the brain metabolizes sugar changes as we age. Although both male and female brain metabolisms slow down over time, the study suggests that men’s may be more sluggish over their lifetimes, which results in a brain that appears older from a metabolic standpoint.
In the study, 121 women and 84 men between the ages of 20 and 82 underwent PET scans that measured the cerebral flow of oxygen and glucose. To determine the brain metabolism of each person, researchers observed how much sugar was being used during what’s called aerobic glycolysis. The metabolic process sustains brain development and maturation through life, but it slows down and eventually plateaus at a low level in a person’s 60s.
The metabolic data was fed into a computer program to calculate brain age. It reported that women’s brains were 3.8 years younger, and men’s brain’s were 2.4 years older, than chronological ages. Even among the study’s youngest participants, who were in their 20s, women’s brains appeared younger than men’s based on their metabolism.
Sex differences during brain development likely set the stage for brain aging later in life. Differences in cerebral blood flow, hormones and gene expression may make the female brain more resilient to aging-related changes.
“It’s not that men’s brains age faster — they start adulthood about three years older than women, and that persists throughout life,” Goyal said.
In a separate phase of the study, researchers turned their attention away from sex differences and looked for links between brain metabolism and Alzheimer’s. They studied whether brains with signs of beta-amyloid plaque, an Alzheimer’s-promoting protein, appeared older than brains that didn’t have this marker. Surprisingly, brains with beta-amyloid plaque didn’t appear older than the other brains.
Researchers say a brain’s beta-amyloid status may not significantly impact brain metabolism, or at least not until until a certain threshold of neurodegeneration is met. It also suggests that brain metabolism has little effect on whether someone develops a complex disease like Alzheimer’s.
Next, the researchers plan to study whether people with more youthful brains are less likely to develop cognitive problems.