NEW YORK (CBS News) — A new study in the American Academy of Neurology finds women who are physically fit may be 90 percent less likely to develop dementia. But is there really a link between a healthy body and mind?

The study tested the fitness of 191 Swedish women at age 50. They were given a fitness test and followed for 44 years. Researchers found the women who were very fit had only a 5 percent chance of developing dementia later in life, compared to much higher rates among women who had lower levels of fitness.

In addition, having higher levels of fitness seemed to delay the onset of dementia. For example, women in the medium fitness group typically developed it at the age of 90, as opposed to 79.

CBS News medical contributor Dr. Tara Narula says there could be a few reasons why.

“Some of it may be the indirect effects of control in cardiovascular risk factors,” Dr. Narula said. “So things like blood pressure, cholesterol, diabetes, obesity, improving blood flow to the brain. However, there may be a component that’s directly affecting the brain where you’re improving the architecture, the wiring, the connectivity and communication going on in the brain itself.”

Because of that, Narula says it’s important to squeeze in any physical activity you can.

“The earlier you start, the better,” she said. “You don’t have to do crazy levels of fitness — we’re talking about 150 minutes a week of moderate-level aerobic activity.”

That’s the recommendation from the American Heart Association, amounting to around 30 minutes of exercise, five days a week.