How does smoking affect olfaction in Parkinson's disease?

Smoke-induced upper airway damage and Parkinson's disease (PD) can be considered independent risk factors for smell impairment. Interestingly, cigarette smoking has been strongly associated with reduced risk of PD and, therefore, has been suggested to have neuroprotective effects. Our pilot study aimed to evaluate the relationship between smoking and olfaction in PD patients and matched controls. Sixty-eight PD patients and 61 healthy controls were categorized in relation to PD diagnosis and current smoking status, and evaluated by means of the Italian version of the University of Pennsylvania 40-item Smell Identification Test (UPSIT-40). ANOVA analysis with post-hoc Bonferroni correction showed that non-smoker controls presented a higher UPSIT-40 total score than smoker controls (p<0.001), non-smoker PD patients (p<0.001) and smoker PD patients (p<0.001). In this view, smoking seems to affect olfaction in controls but not in PD patients, and no significant differences were found when comparing smoker controls, smoker PD patients and non-smoker PD patients. Several epidemiological studies showed a negative effect of smoking on olfaction in the general population. Otherwise the sense of smell is similar in smoker and non-smoker PD patients. These results suggest that PD and smoking are not independent risk factors for impairment of sense of smell, but they might variably interact.