Older adults who exercise for 15 minutes at least three times each week may reduce their risk for dementia by about one-third, according to a report in the January 17 Annals of Internal Medicine. Risk reduction was greatest for those with some physical limitations.

“This study adds to growing evidence that moderate exercise is the closest thing we have to a magic wellness bullet for everyone,” says William H. Thies, Ph.D., Alzheimer’s Association vice president, medical and scientific affairs. “Moderate physical activity has all kinds of benefits and almost no downside.”

The study enrolled 1,740 adults who were at least age 65 and who scored at the upper end of the normal range on a test of cognitive function. Researchers asked participants how many days each week they engaged for at least 15 minutes in activities such as walking, hiking, bicycling and swimming. They also tested participants’ current level of physical condition by timing how long it took them to walk 10 feet and to rise five times from a chair to a standing position, and by testing their balance and the strength of their grip.

Over an average of six years, participants were tested twice each year to identify new cases of dementia. Those who reported exercising at least three times a week were about one-third less likely to develop dementia than those who exercised less often.

By enrolling participants who scored at the upper end of normal on the cognitive test, the researchers lowered the chances of unintentionally including individuals in the earliest stages of dementia. This also reduced the likelihood that the connection between less exercise and dementia occurred because those with very early dementia are apt to decrease their involvement in usual leisure activities, including exercise, prior to diagnosis.

The risk reduction linked to exercise was greatest for participants who had lower levels of performance on the physical function tests. According to an editorial appearing in the journal, this finding underscores the importance of exercise for older adults of all ability levels, especially those who already have some physical limitations.