A recent study conducted by Korean scientists revealed an interesting correlation: quitting smoking may increase the risk of developing Parkinson's disease, despite smokers having a higher overall mortality rate. The results of the study were published in the journal Neurology.
According to many empirical data, tobacco smoking, despite its numerous negative health consequences, shows a negative correlation with the risk of developing Parkinson's disease. One possible reason for this connection is considered to be the protective effects of nicotine and carbon monoxide. However, the high risk of premature death among smokers could influence the results of studies, which has not been sufficiently explored until now.
Jun-Hyuk Lee and his team from Ilji University analyzed data from nearly 410,500 smokers (average age 51.7 years; 93.5% of them were men) who underwent three stages of examination as part of the Korean National Health Screening Program (NHSP) in 2009–2010, 2011–2012, and 2013–2014. The median follow-up after the last examination was 9.1 years, resulting in nearly 3.59 million person-years.
The participants were divided into four groups based on smoking dynamics: current smokers (over 267,000 people), relapsed smokers (about 30,500 people), recent quitters (over 54,000 people), and long-term quitters (about 58,500 people). Information on new cases of Parkinson's disease and mortality was collected from relevant national registries, and statistical processing was conducted using Fine-Gray competing risks regression models, taking into account confounding factors.
During the study, Parkinson's disease was identified in 1,794 participants (0.44%), and 31,203 participants (7.6%) died. The analysis results showed that the risk of developing Parkinson's disease was significantly higher among recent and long-term quitters (sub-distribution hazard ratios were 1.60 and 1.61, respectively; p < 0.001). For those who resumed smoking, the risk did not differ from that of current smokers (1.05; p = 0.603). At the same time, long-term quitters had a significantly lower risk of death from all causes (0.83; p < 0.001), while recent quitters showed a reduction that was borderline statistically significant (0.97; p = 0.038), and no differences were observed among relapsed smokers (0.97; p = 0.217).
Based on the obtained data, the authors of the study conclude that the risk of developing Parkinson's disease primarily depends on current smoking status rather than accumulated exposure to tobacco smoke. The protective effect of smoking persists even considering the increased mortality and is observed with short-term (about two years) smoking cessation. Mortality trends confirm the benefits of early smoking cessation, and data on the protective effect open up opportunities for further exploration of mechanisms and the development of safe cholinergic agents for the prevention and treatment of Parkinson's disease.
Previously conducted studies have shown that vaccination against tetanus may be associated with a reduced risk of Parkinson's disease, while the presence of ulcers and damage to the mucous membranes of the upper gastrointestinal tract increases this risk. Additionally, living in green areas in old age is associated with fewer first hospitalizations for Parkinson's and Alzheimer's diseases.
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