Risk factors for Parkinson's disease and impaired olfaction in relatives of patients with Parkinson's disease.

Our objective was to assess the association between risk factors for Parkinson's disease (PD) and abnormal olfaction in first-degree relatives of patients with PD. Factors including lower cigarette smoking and lower caffeine consumption have been associated with increased risk of PD. Idiopathic hyposmia has also been associated with an increased risk of PD. The relationship between risk factors for PD and impaired olfactory function has not been evaluated in relatives of PD patients. We conducted a mail survey of odor identification ability in 173 first-degree relatives of PD patients using the 40-item University of Pennsylvania Smell Identification Test (UPSIT). Respondents also completed a questionnaire inquiring about risk factors for PD including caffeine consumption, tobacco use, exercise, and exposures to heavy metals, well-water, and pesticides. There was a direct relationship between olfactory performance and lifetime caffeine intake. After adjustment for age, gender, and smoking status, subjects who reported drinking 2 to 3 cups of caffeinated beverages per day (2.6 points higher 95% CI: 0.5, 4.5) and 4 or more cups per day (3.7 points higher, 95% CI: 0.6, 6.7) had significantly better UPSIT scores than those who consumed less than 1 cup per day. There was no significant relationship between olfactory performance and other risk factors. In conclusion, abnormal olfaction is associated with significantly lower lifetime caffeine consumption in first-degree relatives of PD patients. Further research is warranted to determine whether a history of lower caffeine consumption confers additional risk for the development of PD in hyposmic relatives of PD patients.