Large study: Quitting smoking linked to increased risk of Parkinson’s
But stopping and staying smoke-free cuts risk of death – a 'clear' benefit
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- Quitting smoking increases the risk of Parkinson's disease but significantly lowers overall death risk, a large study found.
- Smoking's protective effect against Parkinson's is outweighed by severe health risks, according to scientists.
- Research is aiming to identify smoking components for use in safe Parkinson's therapies.
Quitting smoking was linked to a greater risk of Parkinson’s disease compared with continuing to smoke, but it was also associated with a smaller risk of death — especially among those who quit and remained smoke-free — in a large-scale study conducted in South Korea.
These new data come from an investigation that involved more than 400,000 current and former smokers who were part of a health screening program in the Asian nation. The researchers found a 60% greater risk of Parkinson’s among quitters versus so-called persistent smokers.
“While our study found smokers who quit showed a higher risk of Parkinson’s disease than those who were currently smoking, it also found they had a lower risk of death,” Jun-Hyuk Lee, MD, PhD, of the Eulji University School of Medicine in Seoul and a study author, said in a press release from the American Academy of Neurology announcing the study’s findings.
Lee stressed that “the health benefits of quitting smoking remain substantial and clear” despite the greater likelihood of developing Parkinson’s.
Still, tapping into what part of cigarette smoking shows protective effects against the neurodegenerative disease may help in developing treatments for disease prevention, according to the researchers.
Their study, “Dynamic Smoking Patterns and Risk of Parkinson Disease and All-Cause Mortality,” was published in the journal Neurology.
Across several lines of research, people who smoke have been shown to have a lower risk of developing Parkinson’s, a disease caused by by the progressive loss of nerve cells in the brain involved in motor control.
Probing the links between smoking status, death, and Parkinson’s
To help explain these findings, a recent U.S. study suggested that low doses of carbon monoxide, a gas present in cigarette smoke — which is otherwise lethal at higher doses — may help prevent Parkinson’s by activating protective mechanisms in the brain.
Nevertheless, it’s well established that smoking can lead to several health problems and premature death, potentially leading to a competing risk that masks the true relationship between smoking and Parkinson’s, according to the researchers.
“The severe health risks of smoking cannot be overlooked, as it remains a leading cause of preventable death and contributes to heart disease, cancer and chronic lung disorders,” Lee said.
Data show that cigarette smoking status often changes over time, with about half of adults having attempted to quit smoking within the previous year, according to a 2017 U.S. nationwide survey. As such, the long-term impact of changes in smoking status among current smokers on the risk of Parkinson’s remains unclear.
To address this gap, the research team investigated the association between changes in smoking status and the risks of Parkinson’s and all-cause mortality (death by any cause) in a large group of smokers.
The scientists identified more than 410,000 smokers aged 40 and older in the South Korean National Health Screening Program. Among the study group, the mean age was 51.7. Men accounted for nearly all (93.5%) of the total population. Participants were grouped as persistent smokers, relapsed smokers — those who had quit but resumed smoking — recent quitters, or sustained quitters.
Over a median follow-up of 9.1 years, the team identified 1,794 new cases of Parkinson’s, representing 0.44% of the study population. During the same time, 31,203 participants (7.60%) died from any cause.
Risk of death 17% lower for sustained quitters vs. persistent smokers
When the researchers examined the data, the risk of developing Parkinson’s was found to increase steadily with age in all smoking groups, with differences diverging in mid-adulthood.
Sustained quitters and recent quitters had the highest rates of Parkinson’s over time, while persistent smokers had the lowest observed risk. By age 100, the cumulative incidence of Parkinson’s was double for sustained quitters than for persistent smokers (0.47% vs. 0.24%).
In contrast, the pattern for overall death rates was different. Mortality increased with age in all groups, but persistent and relapsed smokers had higher death rates than recent and sustained quitters. At older ages, these differences narrowed as the groups’ risk levels converged, with death rates similar by age 100 (5.2% vs. 4.5%), the data showed.
The team then compared the risk of developing Parkinson’s and the risk of death among the different smoking groups, using persistent smokers as the reference group.
After adjusting for other health and lifestyle factors, recent quitters had a 60% higher risk of Parkinson’s and sustained quitters a 61% higher risk than persistent smokers. On the other hand, relapsed smokers showed a similar risk as persistent smokers.
The pattern was different for overall mortality. After adjustment, sustained quitters continued to show a significantly lower risk of death — 17% lower than persistent smokers. Recent quitters had a slightly lower risk of death, but this difference was small (3%). Relapsed smokers no longer showed a significant difference from persistent smokers in death risk.
“Overwhelming evidence from multiple previous studies shows quitting smoking is much better for long-term health overall. … Our study suggests a lower risk of Parkinson’s is not necessarily associated with how long someone smokes, but rather if they are currently smoking.
One key study limitation, according to the researchers, was that the data were self-reported, meaning some participants may not have remembered or reported their information accurately. In addition, most participants were Korean men, so the findings may not apply equally to women or to people from other backgrounds.
Nonetheless, the data contribute to researchers’ understanding of the impact of smoking on Parkinson’s risk, per the team.
“Overwhelming evidence from multiple previous studies shows quitting smoking is much better for long-term health overall,” Lee said. “Our study suggests a lower risk of Parkinson’s is not necessarily associated with how long someone smokes, but rather if they are currently smoking.”
According to Lee, the key to future research is determining if the protective effects of smoking on Parkinson’s risk can be tapped in some other way.
“Future studies are needed to better understand which components of smoking contribute to the reduced risk, and to develop safe and targeted therapies that replicate the effects of smoking for Parkinson’s without the harmful health consequences,” Lee said.
