A recent study conducted by Korean scientists has revealed a link between smoking cessation and an increased risk of developing Parkinson's disease. These results were published in the journal Neurology and even take into account higher mortality rates among smokers.
Despite the numerous health risks associated with tobacco smoking and increased mortality, there is an inverse correlation between smoking and the likelihood of developing Parkinson's disease. This phenomenon has been repeatedly confirmed by empirical data. Scientists suggest that the potential protective properties of nicotine and carbon monoxide may explain this connection. However, it is worth noting that the aforementioned risk of premature death among smokers may distort the actual picture, as it represents a competing risk that has long remained outside the focus of research.
In the study conducted by Jun-Hyuk Lee from Ilji University and his team, nearly 410,500 smokers participated (average age 51.7 years; among them, 93.5 percent were men). Participants underwent three examinations as part of the Korean National Health Screening Program (NHSP) from 2009 to 2014. The median follow-up period after the last examination was 9.1 years, resulting in nearly 3.59 million person-years.
Smokers were divided into several groups: continuing to smoke (more than 267,000 people), resumed smoking (about 30,500 who did not smoke at the second examination and started again at the third), recently quit (more than 54,000 who smoked at the second and did not smoke at the third), and persistently quit (about 58,500 who did not smoke at either the second or third examination). Information on new cases of Parkinson's disease and mortality was collected from national registries. The data were processed using Fine-Gray competing risks regression models, adjusting for confounding factors.
During the follow-up, 1,794 participants (0.44 percent) were diagnosed with Parkinson's disease, and 31,203 people (7.6 percent) died. The results showed that both recently and persistently quit smokers have a significantly increased risk of developing Parkinson's disease (sub-distribution hazard ratios of 1.60 and 1.61, respectively; p < 0.001), while for those who resumed smoking, this risk did not differ from that of continuing smokers (1.05; p = 0.603). At the same time, persistently quit smokers had a significantly reduced risk of death from all causes (0.83; p < 0.001), while for recently quit smokers, this reduction was marginally significant (0.97; p = 0.038), and for those who resumed smoking, no significant differences were observed compared to continuing 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 largely depends on the current smoking status rather than the cumulative exposure to tobacco smoke. The protective effect of smoking persists even when considering the increased mortality and remains relevant during a short period of abstinence from smoking (about two years). Trends in mortality confirm the benefits of early smoking cessation, and the identified protective effect opens up opportunities for further exploration of its mechanisms and the development of safe cholinergic agents for the prevention and treatment of Parkinson's disease.
Previous studies have also indicated a link between tetanus vaccination and a reduced risk of Parkinson's disease, while ulcers and damage to the mucous membrane of the upper gastrointestinal tract increase the risk, and living in a green area in old age reduces the number of first hospitalizations for reasons related to Parkinson's and Alzheimer's diseases.
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