A large prospective study -- perhaps the most definitive yet of the relationship between exercise and dementia -- found that older adults who exercised at least three times per week were less likely to develop dementia than those who were less active (Article, p. 73). The study participants were 65 or older with normal mental function at the beginning of the study. They were followed for six years. Of the 1,740 subjects, 158 developed dementia, including 107 who developed Alzheimer’s disease. Statistically, the annual rate of dementia was 13.0 per 1,000 person-years for people who exercised three or more times per week, compared with 19.7 per 1,000 person-years for those who exercised fewer than three times per week. An editorial writer says that future research should try to determine whether exercise causes a lower rate of dementia or whether physical activity is a proxy for "life engagement" or other lifestyle or sociodemographic characteristics that are truly associated with development of dementia (Editorial, p. 135). Also needed is research to determine the "type, frequency, intensity or duration of physical activity that is most beneficial in preventing cognitive deterioration."