Adults aged 65 years and older, a group at high risk for developing dementia, will soon be the fastest growing age segment in the United States, the article notes. Some studies suggest that exercise may reduce the risk of cognitive decline. However, the intensity of exercise needed to maintain cognitive function is uncertain.

Jennifer Weuve, Sc.D., Harvard School of Public Health, Boston, led the research group that surveyed 18,766 70-81 year old women on their physical activity in biennial questionnaires beginning in 1986.

Telephone interviews with the women were conducted from 1995 to 2001, testing general cognition, verbal memory, category fluency, and attention. The women were participants in the Nurses' Health Study, a survey begun in 1976, designed to assess medical history and health-related behaviors.

The researchers found that higher levels of physical exercise were linked to better cognitive performance.

The women were divided into five groups, depending on their average energy expenditures, one being the lowest and five the highest. Groups two through five scored higher on the cognitive performance tests than those in group one.

Also, those in the highest activity grouping had a 20 percent lower risk of cognitive impairment than those in the lowest. Women who walked at an easy pace for at least 1.5 hours per week had higher cognitive scores than those who walked less than forty minutes per week. Women in the two groups with the highest rates of physical activity had significantly less cognitive decline than women with the lowest rate of physical activity.

" ... [T]he apparent cognitive benefits of greater physical activity were similar in extent to being about three years younger in age and were associated with a twenty percent lower risk of cognitive impairment. The association was not restricted to women engaging in vigorous activities ...," the authors say in their report.

"In summary, in our study, as well as in other epidemiologic investigations, higher levels of physical activity, including walking, are associated with better cognitive function and less cognitive decline," the researchers conclude.

Robert D. Abbott, Ph.D., of the University of Virginia School of Medicine, Charlottesville, Virginia, and colleagues examined the association between walking and future risk of dementia in older men.

Evidence suggests that physical activity may be related to the clinical expression of dementia, the article states. Whether the association includes low-intensity activity, such as walking, has not been known.

The study included 2,257 physically capable men aged 71-93 years in the Honolulu-Asia Aging Study. Distance walked per day was assessed from 1991 to 1993. Follow-up for incident dementia was based on neurological assessment at 2 repeat examinations (1994-1996 and 1997-1999).

The researchers found that after adjusting for age, men who walked the least (less than 0.25 mile/day) experienced a 1.8-fold excess risk of dementia compared with those who walked more than 2 miles/day. Men who walked 0.25 to 1 mile/day experienced a 71 percent increased risk of dementia compared to men who walked the most (more than 2 miles/day).

These associations persisted after accounting for other factors, including the possibility that limited amounts of walking could be the result of a decline in physical function due to preclinical dementia.

"There are no clear explanations for the relation between walking and dementia," the authors write. "Although associations were independent of other study characteristics that were determined at the time when walking was assessed, it may be that men who walk frequently are more resistant to risk factor changes or transitions into adverse risk factor states.

"Although changes in risk factor status in the course of follow-up were not considered in the current study (nor were such data always available), it would be important to determine if men who walk regularly are less prone to development of intervening conditions that have a closer link with dementia," say the authors.

"Although complex, this study and past evidence suggest that walking and active lifestyles in general are associated with a reduced risk of dementia," the researchers conclude.