Exercise helps reduce dementia

ReviewSEATTLE, Jan. 16 - Older adults who exercise three or more times a week have a 30% to 40% lower risk of developing dementia than their more sedentary counterparts, reported investigators here.

In other words, exercising the body also appears to keep the mind nimble, Eric B. Larson, M.D., and colleagues at the Group Health Cooperative here suggested in a prospective cohort study published in the Jan. 17 issue of the Annals of Internal Medicine.

They followed more than 1,700 adults ages 65 years and older with normal mental function for six years, and found that the rate of dementia for those who exercised more than three times each week was 13.0 per 1,000 person-years, compared with 19.7 per 1,000 person years for those who exercised less often. The study only measured frequency and did not quantify exercise.

"We learned that a modest amount of exercise would reduce a person's risk of dementia by about 40%," said Dr. Larson. "That's a significant reduction." The age- and sex-adjusted hazard ratio of dementia was 0.62 (95% CI, 0.44 to 0.86; p=0.004). The shape of the survival curves suggested to the investigators that exercise did not prevent dementia but rather led to a delay in onset.

Those who benefited the most were frailest at the start of the study, Dr. Larson continued. "So this means that older people really should 'use it even after you start to lose it,' because exercise may slow the progression of age-related problems in thinking."

The study is the "first to report an interaction between level of physical function and physical activity and dementia risk," wrote Laura Podewils, Ph.D., of the CDC and Eliseo Guallar, M.D., Dr.PH., of the Johns Hopkins Bloomberg School of Public Health in an accompanying editorial.
Dr. Larson and colleagues conducted a prospective study of 1,740 members of the Group Health Cooperative who were age 65 and up and cognitively normal at baseline.

The participants were asked to report the number of days a week that they engaged in at least 15 minutes of physical activity, including walking, hiking, bicycling, aerobics, or weight training.
The study participants were followed for a mean of 6.2 years between 1994 and 2004. They were assessed for cognitive function and dementia every two years.

At six years, 107 participants were diagnosed with Alzheimer's disease, and 51 were determined to have other forms of dementia.

The investigators found that for those who exercised three or more times weekly the rate of dementia was 13.0/1000 person-years, compared with 19.7/1000 person-years for those who exercised fewer than three times weekly. The difference between the groups translated into a 32% reduction in risk for the more active group.

While the study does not demonstrate a causative effect of exercise on dementia risk, it supports results of other observational studies showing an association between exercise and reduced risk of cognitive decline, noted Dallas Anderson, Ph.D., program director for population studies in the National Institute of Aging's Dementias of Aging Branch, which funded the study.
"Physical activity has been shown to be beneficial for health and aging in a number of areas," Dr. Anderson said. "This emerging association between exercise and cognitive health is increasingly important to understand."

It's possible that exercise is a proxy for social interaction or other lifestyle factors that could help stave off dementia, Drs. Podewils and Guallar commented in their editorial. They called for randomized trials and additional research into the specific types, frequency, intensity and duration of exercise that could be most helpful for preventing cognitive decline.

Exercise may help to ward off dementia by improving cerebrovascular blood flow to brain regions involved with memory, Dr. Larson suggested.

"Earlier research has shown that poor blood flow can damage these parts of the brain. So one theory is that exercise may prevent damage and might even help repair these areas by increasing blood flow" he said.

"Even if you're 75 and have never exercised before, you can still benefit by starting to exercise now," he added.

Primary source: Annals of Internal MedicineSource reference: Larson EB et al. Exercise Associated with Reduced Risk of Dementia in Older Adults, Ann Intern Med 2006; 144: 73-81. Additional source: Annals of Internal MedicineSource reference: Podewils Lj and Guallar E. Mens Sana in Corpore Sano. Ann Intern Med 2006; 144: 135-7.