FRIDAY, Jan. 23, 2015 (HealthDay News) -- Young women who regularly exercise may have more oxygen circulating in their brains -- and possibly sharper minds, a small study suggests.

The findings, from a study of 52 healthy young women, don't prove that exercise makes you smarter, researchers said.

On the other hand, it's "reasonable" to conclude that exercise likely boosts mental prowess even when people are young and healthy, said Liana Machado, of the University of Otago in New Zealand, the lead researcher on the study.

Previous studies have found that older adults who exercise tend to have better blood flow in the brain, and do better on tests of memory and other mental skills, versus sedentary people of the same age, the authors point out.

But few studies have focused on young adults, they said. The women in this study were between 18 and 30.

The "predominant view" has been that young adults' brains are operating at their lifetime peak, no matter what their exercise level, the researchers write in the journal Psychophysiology.

But in this study, brain imaging showed that the oxygen supply in young women's brains did vary depending on their exercise habits.

Compared with their less-active peers, women who exercised most days of the week had more oxygen circulating in the frontal lobe during a battery of mental tasks, the study found.

The frontal lobe governs some vital functions, including the ability to plan, make decisions and retain memories longer-term.

Machado's team found that active women did particularly well on tasks that measured "cognitive inhibitory control."

"That refers to the ability to suppress reflexive responses and instead respond strategically, using self-control," Machado explained.

That skill turns up a lot in daily life, she noted, whether in playing a video game or driving a car.

Similarly, the researchers found a link between higher brain oxygen levels and women's performance on the toughest test in the battery -- where the challenge was to combine inhibitory control with multitasking.

None of that proves cause-and-effect, Machado said.

But, she added, "it seems reasonable to deduce that a causal relationship likely exists -- where regular physical activity increases oxygen availability in the brain, which in turn supports better cognitive performance, particularly for more challenging tasks."

Another researcher said that when it comes to exercise and brain health, there is always a "chicken-or-egg" question.

It's possible that the young women who did better on the mental tasks were more likely to choose healthy habits because the frontal lobe is involved in "orchestrating a plan," said Sandra Bond Chapman, chief director of the Center for BrainHealth at the University of Texas at Dallas.

Chapman, who was not involved in the study, said it would be helpful for researchers to follow groups of people long-term to see whether those who adopt healthy habits end up sharpening their mental skills.

That said, Chapman encouraged people to lace up their sneakers and "get moving."

"There is growing scientific evidence that physical exercise is good for the body and the brain, no matter the age," she said.

And how much exercise would be enough to benefit a young person's brain? It's not clear, said Machado.

Women in this study were considered to be meeting guidelines on regular exercise if they got at least 30 minutes of moderate activity (such as brisk walking) or 15 minutes of vigorous activity (such as running) at least five days a week.

So the findings suggest that moderate amounts of exercise would "suffice," Machado said. "But it will be important to test whether more vigorous exercise affords greater benefits," she added.

Future studies should also focus on young men, Machado said, since women and men differ in the way the brain's vasculature (system of blood vessels) functions.

"It can't be assumed that similar findings will arise in men," she said.

More information

The Society for Neuroscience has more on exercise and the brain.