Background: The association between physical activity and risk of neurodegenerative diseases is not well established. We therefore aimed to quantify this association using meta-analytical techniques.
Method: We searched Medline, the Cochrane Database of Systematic Reviews and Web of Science databases from 1990 to 2007 for prospective epidemiological studies of physical activity and incident dementia, Alzheimer's and Parkinson's disease. We excluded studies of physical activity and cognitive decline without diagnosis of a neurodegenerative disease. Information on study design, participant characteristics, measurement of exposure and outcome variables, adjustment for potential confounding, and estimates of associations was abstracted independently by the two investigators.
Results: We included 16 prospective studies in the overall analysis, which incorporated 163797 non-demented participants at baseline with 3,219 cases at follow-up. We calculated pooled relative risk (RR) using a random effects model. The RR of dementia in the highest physical activity category compared with the lowest was 0.72 [95% confidence interval (CI) 0.60-0.86, p<0.001], for Alzheimer's, 0.55 (95% CI 0.36-0.84, p=0.006), and for Parkinson's 0.82 (95% CI 0.57-1.18, p=0.28).
Conclusions: Our results suggest that physical activity is inversely associated with risk of dementia. Future studies should examine the optimal dose of physical activity to induce protection, which presently remains unclear.