A study analyses the relationship between quitting smoking and the risk of developing Parkinson's disease

The study is of good quality. The design is adequate and the methodology is generally correct. Neurology is a very good journal and publishing there generally implies that the article is well done.

It was already well known that smoking less was associated with a higher relative risk of Parkinson's disease. In fact, it had been suggested as a possible protective factor against the disease, associated with the effect of nicotine. But the truth is that the reason for this is unknown. What was suspected, and in fact the authors also mention this, is that in people at risk of Parkinson's disease or who are in a very early pre-diagnostic phase, there is already a dopamine deficit and, therefore, also a deficit in the reward circuit and addiction mechanisms. In other words, it is easier for them to quit smoking because they already have biological deficits related to the disease (as I said, dopamine deficiency), not because quitting smoking increases their risk. In favour of this hypothesis is the fact that what modifies the risk is whether or not they quit smoking, not how much they have smoked.

[As for possible limitations] Fundamentally, it is a retrospective study and, as in all epidemiological studies of this type, it is not possible to control for all the genetic and environmental factors that may influence risk. In any case, the authors partially counteract this by including a huge sample and controlling for the most well-known factors (age, physical activity, blood pressure, cholesterol, etc.).

Beyond these statistical nuances, what is clear is that continuing to smoke increases mortality (and certainly morbidity as well). Regardless of the underlying cause of why people who quit have a higher incidence of Parkinson's disease, smoking is bad for your health.

The study recently published in Neurology shows, based on data obtained from a large number of patients with a history of tobacco use, including people who had quit smoking, new evidence of the link between tobacco use and the incidence of Parkinson's disease. It was already known that this neurodegenerative disorder is somewhat more common among smokers than non-smokers, and this new study shows that those who quit smoking for a long time significantly reduced all-cause mortality compared to those who continued smoking, but had a slightly higher incidence of Parkinson's disease.

There is irrefutable evidence that tobacco seriously harms both human health and the planet: tobacco causes around 60,000 deaths per year in Spain and is one of the main preventable causes of respiratory and cardiovascular diseases and cancer, and it also has a serious impact on the environment. In contrast to the seriousness of the damage caused by tobacco, studies have been published indicating that the incidence or clinical course of a few disorders—including Parkinson's—may be somewhat lower among smokers than among non-smokers. These potential benefits are negligible compared to the harms of tobacco and nicotine use and exposure, so rather than questioning the need to continue supporting measures to prevent smoking initiation and facilitate cessation among those who still smoke, they merely encourage further research to help develop new therapies that replicate the possible beneficial effects of tobacco on diseases such as Parkinson's.