Projection of the prevalence of Parkinson's disease in the coming decades: Revisited

Objective: Previous studies have estimated future PD prevalence based on population aging. This study revisits that projection by accounting for the potential impact of declining rates of smoking. Methods: The age- and gender-stratified smoking prevalence in the United States from 2000 to 2040 were obtained from the U.S. Census Bureau and the U.S. Surgeon General's Smoking Report. PD prevalence was estimated based on population aging with and without an account of the impact of declining smoking rates. Relative risks of 0.56 and 0.78 were applied for current and former smokers, respectively. Results: Accounting for aging alone, ∼700,000 PD cases are predicted by 2040. After accounting for the declining smoking prevalence, ∼770,000 cases, an increase of ∼10% over the estimate without smoking, is predicted. Conclusions: If the epidemiological association of smoking and PD is causal, projecting future cases without considering smoking may underestimate disease burden, underscoring the urgency of adequate resource allocation.