Larson EB, Wang L, Bowen JD, et al. Exercise is associated with reduced risk for incident dementia among persons 65 years of age and older. Ann Intern Med. 2006;144: 73-81.

Sedentary older adults are more likely to develop dementia than their peers who exercise, according to new research. The risk reduction is greatest in adults who are the least physically fit. This article suggests that adults who walk just three times per week for 15 minutes will cut their risk of dementia. The study involves 1,740 subjects who were at least 65 years of age at enrollment. The subjects had no evidence of cognitive impairment at baseline and scored above the 25th percentile on a standard cognitive function screening test. The participants were evaluated every 2 years to determine incident dementia. During a mean follow-up of 6.2 years, 158 subjects developed dementia, including 107 with Alzheimer's disease. The rate of dementia among adults who exercised at least 3 times per week was 13.0 per 1,000 people-years-significantly lower than the rate seen among less active adults, which was 19.7 per 1,000 people-years (P = 0.004). While regular exercise may not prevent dementia altogether, the authors noted that simply delaying the onset might be enough, considering that it is generally a disease of older adults.