Nicotine exposure and Parkinson disease.

The observed inverse relationship between smoking and Parkinson disease has prompted suggestions that nicotine, a centrally active agent, might protect against the disease. In this case-control study, cases were found to have ever regularly smoked cigarettes significantly less frequently than sex-, race-, and age-matched neighbors. This report analyzes the detailed smoking histories of cases and neighbors to see if these histories support the nicotine protection hypothesis. Estimated nicotine exposure before age at onset of symptoms for smoking cases was 186.1 g; for smoking controls it was 208.3 g (p = 0.34). Among the cases, severity of disease was not related to the extent of nicotine exposure before disease onset. Age at onset of symptoms for smoking cases (52.7 years) was not delayed (57.8 years for nonsmoking cases). Since the study was unable th find further support for the nicotine protection hypothesis, it is concluded that the observed inverse relationship between smoking and Parkinson disease is likely explainable by other factors, such as selective mortality or pre-morbid behavioral and/or constitutional changes.