ALLENTOWN, Pa. -

Multiple studies now say regular exercise is the most effective single lifestyle choice people can make to reduce their risk of dementia.

We know exercise is good for you but research is pretty convincing that getting up and moving is one of the best ways to prevent loss of brain function as we age.

Eighty-five-year-old Nancy Koehler tries to exercise a few times a week for one simple reason:

"Because I want to be around. I have grandchildren. I have college graduations to go to; a high school graduation this year," she says.

Nancy lives at Phoebe Terrace in Allentown where brain health is something doctors are always working on. Besides this workout room, there's a brain fitness center where residents can work their cognitive muscles.

Dr. Kelly Carney is the executive director of the Phoebe Center for Excellence in Dementia. She points to many studies that say exercise can greatly reduce a person's risk of dementia.

"Exercise improves blood flow to the brain. Exercise also reduces inflammation in the body. Exercise is good for your heart and all of those things are good for your brain," she says.

How much exercise do you need? Dr. Carney say 30 minutes a day five times a week of moderate exercise should do it, but it can be modified for each person.

"Anything --even chair exercises, chair yoga --which is very gentle. Anything that moves the body increases heart rate, increases flexibility, is very important."

Some studies say moderate exercise will actually increase the size and function of the parts of the brain most responsible for memory.

There is even evidence that exercise can improve the cognitive function of people who are already starting to decline.

"So the more we can get oxygen and nutrients to the brain, the better a person is going to be able to think and function," says Dr. Carney.

If you’re still not convincd -- another study found physically fit mid-lifers are 40 percent less likely to develop dementia than their peers who don’t exercise.