Being active has been associated with a decreased risk of dementia. And some studies find that being active may reduce the risk of Alzheimer's disease. Now a new study suggests that it's not how much activity but how many activities a person engages in that reduces their risk.

The key may be getting involved in a wide variety of activities, from gardening and household chores to walking, say researchers.

Constantine G. Lyketsos, MD, found that older people who participated in various activities were less likely to develop Alzheimer's disease and other types of dementia.

"We don't yet know why this association exists or what causes it. It could well be that maintaining a variety of activities keeps more parts of the brain active, or that this variety reflects better engagement in both physical and social activities," says Lyketsos, professor of psychiatry and behavioral sciences at Johns Hopkins University School of Medicine, in a news release.

More Activities, Less Dementia

Researchers evaluated more than 3,300 people age 65 and over for a wide variety of activities including walking, household chores, yard work, hiking, dancing, bowling, and golfing as well as regular exercise, such as jogging and aerobics.

Walking and household chores were the most common activities. About one-third were active in gardening, yard work, or an organized exercise program.

The participants were followed for about six years, with 14 percent developing dementia during that time.

Being involved in a wider variety of activities was associated with a lower risk of developing Alzheimer's or other types of dementia.

Compared to people involved in one or no activity:

Being involved in two or three activities decreased the risk by about 10 percent Being involved in four activities decreased the risk by nearly 40 percent.

The study appears in the April 1 issue of the American Journal of Epidemiology.

How Activity Protects the Brain

A mounting body of evidence supports the view that physical activity can help maintain memory and mental function. According to the researchers, activity may:

—Increase nerve connections in the brain or release hormones that increase nerve cell creation.

—Lower risk factors for heart disease, such as cholesterol and blood pressure. This may help preserve nerve cells in the brain and mental function.

—Be linked to a more enriched social environment. Previous research has shown that people involved in more social activities are less likely to fall victim to Alzheimer's.

About Alzheimer's

An estimated 4.5 million Americans have Alzheimer's disease, according to the Alzheimer's Association. The number has doubled since 1980, they say, and it's expected to grow significantly as the U.S. population ages.

According to the researchers, the only known risk factors for Alzheimer's are:

—Advancing age

—Family history of Alzheimer's

—Education level. People with lower education are more likely to get dementia.

—Having an Alzheimer's gene, called ApoE e4. In the current study, people with this gene did not gain any protection from Alzheimer's by being involved in various activities.

Other risk factors have also been suggested as a cause of Alzheimer's.

By Michael W. Smith, MD, reviewed by Brunilda Nazario, MD

SOURCE: Podewils, L. American Journal of Epidemiology, April 1, 2005; vol 161: pp 1-13. Alzheimer's Association. WebMD Medical Reference provided in collaboration with The Cleveland Clinic: "Alzheimer's Disease."