The research that we have described thus far has examined mental performance over relatively short periods—just several years. A few studies have begun to look at what happens over longer timescales. In 2003 psychiatrist Marcus Richards of University College London and his colleagues examined in a cohort of 1,919 men and women the influence of self-reported physical exercise and leisure-time activities at age 36 on memory at age 43 and on memory change from ages 43 to 53. Analyses indicated that engagement in physical exercise and other leisure-time activities at 36 was associated with higher memory scores at 43. Physical activity at 36 was also associated with a slower rate of memory decline from 43 to 53 years of age after adjusting for spare-time activity and other variables. The data also suggested little memory protection for those who stopped exercising after 36 but protection for those individuals who began to exercise after this time.

In 2005 then graduate student Suvi Rovio of the Karolinska Institute in Sweden and her colleagues examined the relation between physical activity at middle age and risk of dementia an average of 21 years later, when the cohort was between 65 and 79 years of age. Subjects indicated how often they participated in leisure-time physical activities that lasted at least 20 to 30 minutes and caused breathlessness and sweating. Conducting such activity at midlife at least twice a week was associated with a reduced risk of dementia in later life. Indeed, participants in the more active group had 52 percent lower odds of having dementia than the more sedentary group did.

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