Physical activity and risk of Parkinson's disease in the Swedish National March Cohort.

Physical exercise has been associated with neuroprotective effects in the nigrostriatal dopaminergic system. To examine the impact of physical activity on Parkinson's disease risk prospectively, we followed 43 368 individuals who provided extensive information on physical activity at baseline. We estimated hazard ratios with 95% confidence intervals using Cox proportional hazards regression. During an average of 12.6 years of follow-up, 286 incident Parkinson's disease cases were identified. In males, there was an inverse association with Parkinson's disease for total physical activity (hazard ratio 0.55, 95% confidence interval 0.35-0.87 for medium versus low level), for sum of household, commuting and leisure time exercise (hazard ratio 0.53, 95% confidence interval 0.33-0.85 for high versus low level), and for household and commuting physical activity specifically (hazard ratio 0.50, 95% confidence interval 0.31-0.81 for >6 versus <2 h per week). No association was observed for leisure time exercise or occupational physical activity with Parkinson's disease, among either males or females. Meta-analysis of the present study and five previous prospective studies showed a pooled hazard ratio of 0.66 (95% confidence interval 0.57-0.78) for highest versus lowest physical activity level. Our results indicate that a medium level of physical activity lowers Parkinson's disease risk.