Being a physically fit teen may increase your chances of becoming a mentally fit senior. A new study in the Journal of.

The American Geriatrics Society found that older women who had exercised consistently (at least one period of moderate.

Physical activity– jogging, tennis, etc. a week) during their teen years were sharper mentally than women who got less than that exercise in their youth.

"People who were active as teenagers were 35 percent less likely to be cognitively impaired in late life than those who were inactive," explains study author Laura Middleton with Sunnybrook Health Sciences Center in Toronto.

In the past 10 years researchers have discovered that physical activity at an older age helps to reduce the risk of dementia, but this is one of the only studies to look at the effects of early exercise on mental capacity as we age. Researchers say teen exercise gives the brain an added boost as it develops and repairs its brain cells, called neurons. And this protection seems to stay with us as we age.

"It may be that teenage physical activity, by improving neuroplasticity – or the increase in neurons and connections within the brain – may offer cognitive reserve whereby people can handle more stressors and more disease later in life and still maintain their cognition," explains Middleton.

Middleton says exercise also helps the heart and blood vessels stay healthier which is good for brain power as well.

But don't be discouraged if you weren't an active teen. The researchers, who gathered information from 9,000 women, also found that taking up exercise after the teenage years, even in your 50's and beyond, provided protection for the brain as well.

In fact, the fit adults were 20-25 percent less likely to score poorly on memory, concentration and problem-solving tests than women who never exercised. The benefits seemed to hold true as long as the women got some sort of physical activity at least once a week all year.

This study included only women, but researchers suggested men might experience similar benefits. With the waistlines of children expanding, Middleton hopes her research will add urgency to the need for physical activity for young people. She says our bodies and minds are depending on it. "I think everyone thinks of exercise as work and people have to start seeing physical activity as play again...as a fun and engaging part of anyone's lifestyle," says Middleton.