Smoking, the Sense of Smell and PARKINSON’S DISEASE



Smoking, the Sense of Smell and PARKINSON’S DISEASE

Advice to the general population is that smoking is bad for your health…. very bad, indeed.  But there has been information to the contrary for people with PARKINSON’S DISEASE…some 60 studies report that smokers have a lower risk of developing PARKINSON’S DISEASE.  So, then, what are people with PARKINSON’S supposed to believe?

Smoking, for the general population, is known to lead to lung cancer, Chronic Obstructive Pulmonary Disease (COPD) and ultimately death.  Smoking goes straight through the olfactory system, bypassing any intermediate functions that could serve as a filter, carrying any and all environmental toxins from tobacco or smoke straight to the lungs and the brain.  It is well known that one of the early pre-motor symptoms of PARKINSON’S DISEASE is the loss of sense of smell.  Could smoking possibly be implicated in this?  Could smoking also be an environmental factor implicated in reducing the loss of dopamine producing neurons in the brain?  Can the effects of smoking and early non-motor symptoms help explain the relationship between genetics and environmental factors leading to either neuroprotection or the development and progression of PARKINSON’S DISEASE?

A group of researchers at Pennsylvania State University, Milton S. Hershey Medical Center headed by Xuemei Huang, M.D., Ph.D. developed a study to improve understanding of whether or how smoking affects olfaction in PARKINSON’S DISEASE and how the involvement with olfaction contributes to the development of PD.  They planned their study to. “test the hypothesis that smoking is associated with better olfaction in PARKINSON’S DISEASE.”

Seventy-six people with PARKINSON’S and seventy non- PARKINSON’S control subjects were recruited.  Of the PARKINSON’S subjects, there were 22 with a history of smoking and 54 who had never smoked.  In the control group, 17 were smokers and 53 were non-smokers. The histories of the smoking habits of all subjects were carefully noted.  Only one PARKINSON subject and three of the control subjects were current, active smokers.  While all the smokers had begun smoking in their mid to late teens, by their mid thirties they had stopped smoking.  All subjects were assessed by the mini-mental state examination (MMSE) and the University of Pennsylvania Smell Identification Test (UPSIT).  Non-motor symptoms were also carefully evaluated.

In the PARKINSON’S subject, age of onset was found to be at least 4 years later among the smokers than the nonsmokers.  Control subjects had better results overall for UPSIT smell tests than the PARKINSON’S subjects, however the smoker PARKINSON’S subjects scored better than the nonsmokers.  Smell scores among the PARKINSON’S subjects declined in relationship to age, but decline among the control subjects were not significant.  Women tended to have much better sense of smell than male subjects in the control group, but this was not seen in the PARKINSON’S group.  There was no correlation between the number of cigarettes smoked, the number of years smoked, or the years since the cessation of smoking and the scores of the UPSIT in the PARKINSON’S group, nor was there a correlation between the UPSIT scores and the age of onset or duration of the disease. This study also did not find a relationship between smoking and other non-motor symptoms, such as constipation, etc.

This research has shown some interesting results…that sense of smell in smokers is usually considered to be impaired was not found among the controls, and interestingly, the sense of smell among smokers in the PARKINSON’S group was better than that of the non-smokers.  More interesting, that a history of smoking appears to confer a neuroprotective effect and delays the onset of the disease but that smoking after diagnosis or the use of nicotine patches does not offer the same protection. The results of this study suggest that the protection offered from smoking or nicotine may be a gradual process that occurs over many years before the onset of the motor symptoms.

The authors of this study do show a protective correlation between smoking and the onset of PARKINSON’S DISEASE; however they are aware that there may be other factors, such as personality traits, head trauma, or the use of other medications that may play a role in these results.  Other studies will be needed to verify these results, but this study has made a genuine contribution to understanding the relationship between smoking and PARKINSON’S DISEASE.

Lucasson, E>B>; Sterling, N.W.;Lee, E-Y; Chen, H; Lewis, M.M.; Kong, L; Huang, X.; History of Smoking and Olfaction in Parkinson’s disease.  Early View. Mov. Disord.  doi 10.1002/mds.25912



Review by Marcia McCall


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