The relationship between PA and cognitive function remains unclear. Regarding physiological effects, one hypothesis is that PA can counter age-related decline in cardiovascular function associated with brain hypoxia and consequent cognitive decline.
Dishman suggested that increased oxygenation of the brain may stimulate and protect the central nervous system [15
]. Only a handful of studies have systematically investigated the association between PA and cognitive function. Stewart et al. reported that physically active subjects were 50% less likely to present with cognitive impairment (OR = 0.48; 95% CI= 0.23–1.02) [16
]. Schuit et al. (2001) also found that adults who exercised at least 30 min/day had higher MMSE scores than older adults who did not (p < 0.05) [17
]. This same group showed that carriers of the ε4 allele of the apolipoprotein E (APOE), a genetic risk factor for AD, have a 13.7-fold increase in the risk of cognitive decline (95% CI: 4.2–45.5) if they perform less than one hour of PA per day when compared to non-ε4 carriers who are active. This finding suggests that PA may contribute to modify the deleterious effect on cognition of the APOE ε4 genotype.
Yaffe et al. stratified their subjects according to a self-report questionnaire that provided an estimate of the number of kilocalories (kcal) expended per week or city-blocks ( = 160 m) walked per week [18
]. Women in the highest quartile of activity had an OR of 0.66 (95% CI: 0.54–0.82) of experiencing significant cognitive decline during 6–8 years follow-up when compared to women in the lowest quartile of physical activity. More importantly, the findings of three independent follow-up studies indicate that PA may reduce the risk of dementia in later life [19
]. Laurin et al. showed, in nested case-control study with 4,615 community-dwellers participating in the Canadian Study of Health and Aging, that older subjects engaging in moderate to high levels of PA were less likely to develop cognitive impairment (OR = 0.57, CI: 0.46–0.70) or dementia (OR = 0.58, 95% CI: 0.45–0.76). Older women performing PA of greater intensity than walking more than 3 times a week seemed to benefit the most from the protective effect of PA against AD [21
Randomized control trials looking at the effects of PA on cognition are rare, but the results of two studies are of interest. Emery et al. observed that subjects suffering from chronic airway disease who walked, as exercise, for 10 weeks had significantly better word fluency than non-active controls [22
]. Molloy et al. reported similar findings in an intervention trial investigating older female outpatients after three months of a 45-minute exercise program [23
]. Most of the studies mentioned above recruited individuals who were cognitively normal at the time of entry into the study. These studies had relatively small sample sizes and the measures of cognitive function (such as the MMSE) used were rather crude.