Smoking more cigarettes or for a longer time is associated with a decreased risk of developing Parkinson’s, according to a population-based study.
A reduced risk was also seen in people exposed to passive smoking compared with those who had never smoked.
However, the scientists cautioned that rather than encouraging people to smoke, the findings warrant further research into which compound in tobacco confers this effect.
The study, “Exploring causality of the association between smoking and Parkinson’s disease,” was published in the International Journal of Epidemiology.
The link between smoking and a reduced risk for Parkinson’s is supported by substantial evidence in men and women, and has included cigarette, pipe, and cigar smoking, as well as using smokeless tobacco. Also, children of smokers have shown a lower risk for developing the disease.
However, researchers have recommended considerable caution in interpreting this association as protective. They have been studying a potential effect of personality, in particular whether a low-risk-taking personality would be a confounder, especially if induced by dopamine shortage — a Parkinson’s hallmark — which may make it easier to quit smoking. In this regard, a link between passive smoking and protection from Parkinson’s — which is not susceptible to different personalities — could not be determined.
To better understand this correlation, researchers from Queen Mary University of London, Imperial College London and University of Campania Luigi Vanvitelli, in Italy, analyzed the link between Parkinson’s risk and smoking duration, amount and time since quitting smoking. They looked at a potential delaying effect, smoking patterns among current and former smokers, the association with passive smoking, and the consistency across clinical subtypes.
The study included 220,494 people participating in NeuroEPIC4PD, a prospective European population-based study in 13 centers from eight countries. A total of 715 cases of Parkinson’s (mean age at recruitment 61.4 years, age at onset 67.5) were analyzed.
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Data on smoking habits were collected at recruitment, including whether participants were never, former or current smokers, their age when they started smoking and when they quit, and number of cigarettes per day at different ages.
The results showed that, compared with people who had never smoked, former smokers had a 20% lower risk and current smokers a halved risk for developing Parkinson’s during follow-up (12.8 years).
Smoking more cigarettes and for a longer period of time were also associated with a lower risk of developing the disease, as the risk in people smoking 12 or more cigarettes a day or for longer than 30 years was about 55% lower compared to those who had never smoked.
Smoking correlated with reduced disease risk in both mid-age and late-onset Parkinson’s, as well as in tremor-dominant and akinetic-rigid (slowed movement, muscle stiffness, postural instability, gait impairment) Parkinson’s. Also, the risk did not vary over the follow-up period, which argues against a delaying effect of smoking on Parkinson’s onset, the team observed.
Exposure to passive smoking at home or work was also linked to lower risk, as passive smokers were 30% less likely to develop the disease than non-exposed individuals.
“In conclusion, the present findings are consistent with a protective effect of smoking on the risk of [Parkinson’s],” scientists stated.
“Our discovery is incredibly important from a scientific point of view and should prompt basic science research aimed at identifying the agent responsible for this effect found in tobacco,” Valentina Gallo, MD, PhD. the study’s first author, said in a press release. “Hopefully this will give insight for preventive treatment options.”
“However, no one would ever be advised to use smoking as a preventive treatment for Parkinson’s based on this research, because of the disastrous effects we know smoking has on people’s general health,” Gallo added.