Women tend to have more young brains, at least when it comes to metabolism, than their male counterparts.

While age reduces all brain metabolism, women retain a higher rate throughout their lifetime, researchers reported in the National Academy of Sciences journal Proceedings on Monday.

"Females had a younger brain age compared to males," says Dr. Manu Goyal, an assistant professor of radiology and neurology at the St. Louis Medical School at the Washington University. And that may mean that in later life, women are better prepared to learn and be imaginative.

The result is "great news for many women," says Roberta Diaz Brinton, who was not related to the study and leads the Health Sciences University of Arizona's Center for Excellence in Brain Science. Yet she notes that while the brain metabolism of women is higher overall, certain women's brains are undergoing a dramatic decline in metabolism during menopause, leaving them vulnerable to Alzheimer's.

The study came after Goyal and the brain scans of 205 people whose ages ranged from 20 to 82 were analyzed by a research team. These individuals ' positron emission tomography scans evaluated metabolism by measuring how much oxygen and glucose was used in many different brain locations.

Initially, the team hoped to use the metabolic information to predict the age of a person. So they had a computer study of how male and female metabolism changed.

Then they reversed the process and had an estimate of the age of a person based on data on brain metabolism.

The approach was working. "The age was highly predictive," says Goyal.

Even so, there was a big difference between your brain age and your chronological age for some men. And Goyal says the team was wondering if the difference in men or women was more pronounced.

So they were checking.

"When we looked at males versus females, we found an impact," says Goyal. "In addition, we found females to have a younger brain age compared to males." On average, women's brains appeared about four years younger. Yet why it's not yet obvious.

"It makes us wonder if hormones are involved in the metabolism of the brain and how it ages?" says Goyal. Or is it, like genes, something else?

Whatever the cause, higher metabolism can give an edge to women's brains when it comes to later life learning and creativity, says Goyal.

"But for certain vulnerabilities, it may also set up the brain," he says, including an increased risk of developing Alzheimer's disease.

Brinton has a different view of it. She thinks that the higher brain metabolism of women protects them when they are young from Alzheimer's.

But menopause, she says, causes a "brain energy transition," one that far more affects some women's brain metabolism than others.

Research by Brinton shows that the most likely people to experience a dramatic drop are those who bear a gene variant called APOE4, which raises a person's risk of developing Alzheimer's, or those who have Type 2 diabetes risk factors.

"It's the women who are going to start developing Alzheimer's disease symptoms sooner," she says.

As brain metabolism declines in these women, Brinton says, the sticky proteins associated with Alzheimer's are increasing.

"This is a cycle for some women that starts very early in the aging process," says Brinton. "And we may be able to intervene." The measures are much like those aimed at preventing diabetes, says Brinton. These include food, exercise, and medications that help metabolize sugar in the brain and body.