In 2003, there were almost 40 million Americans aged 65 years or older, representing 12.3% of the US population. By 2030, this population is projected to grow to about 71.5 million people and represent roughly 20% of the population. This is considered the fastest growing segment of the population.

As people age, their risk for most chronic conditions increases. One such condition is dementia , which gradually robs the sufferer of memory, judgment, communication skills and, ultimately, his or her independence. Many individuals who ultimately develop dementia are first diagnosed with a more subtle form of the disease called mild cognitive impairment . These patients can still function independently though they are found to have significant cognitive impairment.

Dementia takes a profound toll—emotionally, physically, and financially—on not only the patient, but his or her family, caregivers, and the healthcare community. Many studies focusing on dementia have considered its causes, treatment, and prevention. A growing body of evidence suggests that physical activity may help delay cognitive decline. A study published in the September 22/29, 2004 issue of the Journal of the American Medical Association looked at the impact of physical activity on the cognitive function of older women.

About the study

The study included more than 18,000 women aged 70 and older. (The women are participants of the ongoing Nurses’ Health Study, which began in 1976 and includes 121,700 registered nurses.) The researchers looked at the women’s physical activity and cognitive functioning.

Physical Activity

Beginning in 1986, and then every two years until cognitive testing began, the women completed questionnaires regarding their physical activity levels. The women were asked to estimate the average amount of time they spent per week doing specific physical activities, such as running, jogging, walking, swimming, biking, and low-intensity exercises like yoga or stretching. The women were divided into five categories based on their level of physical activity: group 1 had the lowest level and group 5 had the highest.

Because walking is one of the most common and practical activities for older adults, the researchers decided to focus on those women who primarily walked for exercise. After excluding subjects who participated in vigorous activities, they ranked the remaining women into the four following groups based on the average amount of walking they did in a week:

  • Less than 38 minutes/week
  • 38 minutes to 1.4 hours/week
  • 1.5 to 2.8 hours/week
  • More than 2.8 hours/week

Cognitive Testing

The cognitive testing was done over the telephone with trained nurses who administered a series of tests designed to assess cognitive function in areas like working memory, attention, and verbal memory. They completed a second set of cognitive tests almost two years later.

The findings

The researchers found that higher levels of activity were associated with better cognitive performance and less cognitive decline. When compared to the group of women with the lowest levels of physical activity, the women with the highest levels had a 20% lower risk of cognitive decline. The study’s authors estimate that the cognitive benefit from physical activity was similar to being about three years younger in age.

When researchers looked at the women who walked regularly but did not participate in vigorous activity, they found significantly higher cognitive scores for the women who walked 1.5 hours or more a week compared to the women who walked less than 38 minutes per week.

Additionally, the researchers found that the women in the highest category of activity were less likely to smoke and report problems with balance, walking, and fatigue compared with the women in the lowest category. Also, the prevalence of cardiovascular disease, diabetes, and pulmonary disease was lower in the more active women.

A second study published in the same issue of the journal looked at walking and dementia in elderly men. The study included more than 2000 men aged 71 to 93. The researchers found that the men who walked the least (less than .25 mile per day) had a 1.8 greater risk of dementia compared with the men who walked more than 2 miles per day—findings that again suggest walking is associated with a reduced risk of dementia.

How does this affect you?

Although the researchers attempted to control for other factors that may conserve cognition in the elderly, it is not possible to conclude from this study that it was the exercise itself that delayed the onset of dementia in these women. Still, it is certainly reasonable to conclude that the preservation of cognitive function is likely to be one of the many benefits of regular exercise—in both women and men. And according to the findings from both these studies, even moderate physical activity—walking as little as 90 minutes per week—can help preserve an aging mind.

If you engage in regular physical activity—keep it up! And if you do not, talk with your doctor about developing an individualized program to get you started on being more active—it will benefit you both physically and mentally.