Does Physical Activity Prevent Cognitive Decline and Dementia?: A Systematic Review and Meta-Analysis of Longitudinal Studies.

By 2050, it has been estimated that approximately one-fifth of the population will be made up of older adults (aged ≥60 years), a group often affected by cognitive decline and dementia, which physical activity may help prevent. We reviewed and synthesised prospective studies into physical activity and cognitive decline, and physical activity and dementia, published until January 2014, using forty-seven cohorts from two previous systematic reviews and an updated database search for meta-analyses, focusing on participants aged ≥40 years, in good health and/or randomly selected from the community, with studies assessed for methodological quality. Twenty-one cohorts on physical activity and cognitive decline and twenty-six on dementia were included, and meta-analysis with the quality-effects model showed that higher physical activity levels reduce the risk of cognitive decline (RR 0.65, 95% CI 0.55-0.76) and dementia (RR 0.86, 95% CI 0.76-0.97) compared to lower levels, though sensitivity analyses adjusting for high-quality studies, OR-reported effect sizes, ≥10 adjustments, and ≥10-year follow-ups suggested a more conservative impact, with an 18% dementia risk reduction (RR 0.82; 0.73-0.91) when excluding one influential study. Longitudinal observational studies indicate this association, supporting a potential causal link, and future research should employ objective activity measures, full confounder adjustments, and adequate follow-up, ideally via randomised controlled trials, while promoting physical activity for its extensive benefits regardless of cognitive effects.