Does physical activity prevent cognitive decline and dementia?: A systematic review and meta-analysis of longitudinal studies

Abstract

BackgroundBy 2050, it has been estimated that approximately one-fifth of the population will be made up of older adults (aged ≥60 years). Old age often comes with cognitive decline and dementia. Physical activity may prevent cognitive decline and dementia.MethodsWe reviewed and synthesised prospective studies into physical activity and cognitive decline, and physical activity and dementia, published until January 2014. Forty-seven cohorts, derived from two previous systematic reviews and an updated database search, were used in the meta-analyses. Included participants were aged ≥40 years, in good health and/or randomly selected from the community. Studies were assessed for methodological quality.ResultsTwenty-one cohorts on physical activity and cognitive decline and twenty-six cohorts on physical activity and dementia were included. Meta-analysis, using the quality-effects model, suggests that participants with higher levels of physical activity, when compared to those with lower levels, are at reduced risk of cognitive decline, RR 0.65, 95% CI 0.55-0.76, and dementia, RR 0.86, 95% CI 0.76-0.97. Sensitivity analyses revealed a more conservative estimate of the impact of physical activity on cognitive decline and dementia for high quality studies, studies reporting effect sizes as ORs, greater number of adjustments (≥10), and longer follow-up time (≥10 years). When one heavily weighted study was excluded, physical activity was associated with an 18% reduction in the risk of dementia (RR 0.82; 0.73-0.91).ConclusionsLongitudinal observational studies show an association between higher levels of physical activity and a reduced risk of cognitive decline and dementia. A case can be made for a causal interpretation. Future research should use objective measures of physical activity, adjust for the full range of confounders and have adequate follow-up length. Ideally, randomised controlled trials will be conducted. Regardless of any effect on cognition, physical activity should be encouraged, as it has been shown to be beneficial on numerous levels.

Physical Activity, Brain Volume, and Dementia Risk: The Framingham Study

“…However, in follow-up longer than a decade (up to 22 years), only available in a subsample of our study population, the relations of baseline physical activity to dementia or AD were not significant and the effect sizes were attenuated. This observation was consistent with a recent systematic review suggesting a weaker protective effect of physical activity in studies with follow-up time longer than a decade (15). In the 10-year follow-up analyses, our reported protective effect appeared strongest for the difference between the lowest physical activity group (Q1) and the more active participants (Q2-Q5).…”

“…Another important aspect of the relation of low physical activity to higher dementia risk is that it has been suggested to be curvilinear with diminishing returns at higher levels of physical activity (15), which may explain why some studies (including the current study) did not report significant associations when physical activity is assessed as a continuous or dichotomous variable. The suggestion of diminishing returns with greater amounts of physical activity is also consistent with findings from two studies with follow-up of more than 20 years (3,18).…”

“…In the Religious Orders Study, an estimate of hours per week spent doing physical activities was not associated with incident AD or decline in cognitive function after 4 years of follow-up, despite a similar analytic design to the one employed in the current study where physical activity was divided into quartiles (7). Thus, although the preponderance of epidemiological evidence supports the link between physical activity and cognitive decline/dementia risk (15), further studies are needed to elucidate this relationship.…”

“…We explored this potential relationship further by determining the risk of incident AD and all-cause dementia in participants who were in the lowest quintile (Q1) of reported PAI versus higher quintiles (Q2-Q5). The decision to treat physical activity variables as continuous and in quintiles was determined a priori due to previous suggestion of potential nonlinear relationships of physical activity to dementia risk (15). All analyses were adjusted for age and sex, and then additionally for apolipoprotein (APO)Eε4 allele status, plasma homocysteine, diabetes, and prevalent cardiovascular disease including stroke.…”

A systematic review of economic analyses of active transport interventions that include physical activity benefits

“…Physical inactivity increases the risk of many adverse health conditions, including obesity, coronary heart disease, stroke, breast and colon cancer, diabetes, dementia and depression (2)(3)(4). Rates of physical inactivity are high worldwide, with technological progress meaning that we now spend less energy in our everyday lives than our predecessors (5,6).…”