Quitting Smoking Raised Parkinson s Risk but Cut Death Risk in 410,000-Person Study
The relationship between tobacco smoking and Parkinson's disease has puzzled neurologists for decades. Epidemiological studies have consistently found that smokers develop Parkinson's at lower rates than non-smokers - a pattern so robust that researchers have spent considerable effort trying to identify which compounds in cigarette smoke might confer the apparent neuroprotective effect. Nicotine is the leading candidate, but the mechanism has not been confirmed.
A study published in Neurology examines this paradox from a new angle: not comparing smokers to non-smokers, but tracking what happens when smokers change their behavior over time. The study included more than 410,000 adult smokers in South Korea, followed for an average of nine years, with health screenings at baseline, roughly two years later, and again two years after that. Participants were classified into four groups based on whether they continued smoking, relapsed after quitting, quit recently, or sustained a quit throughout.
The Parkinson's Finding
During the study, 1,794 people developed Parkinson's disease. Breaking that down by group: 0.33% of persistent smokers, 0.41% of relapsed smokers, 0.67% of recent quitters, and 0.71% of sustained quitters. After adjusting for income, alcohol use, and physical activity, recent quitters and sustained quitters had 60-61% higher Parkinson's risk compared to persistent smokers. Relapsed smokers - those who quit then resumed - had a risk similar to persistent smokers, not to quitters.
This pattern suggests the Parkinson's association is tied to whether smoking is currently occurring rather than to cumulative lifetime exposure. A person who smoked for 30 years and recently quit appears to face higher Parkinson's risk than someone still smoking, regardless of shared history.
Study author Jun-Hyuk Lee, MD, PhD, of Eulji University School of Medicine, offered a cautious interpretation: "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."
The Mortality Finding
The study also tracked deaths: 31,203 participants died across all groups. Persistent smokers had the highest mortality rate at 7.24%, followed by relapsed smokers at 8.09%, recent quitters at 8.76%, and sustained quitters at 7.91%. After statistical adjustment, sustained quitters had a 17% lower risk of death compared to persistent smokers.
The mortality benefit of quitting substantially exceeds the Parkinson's risk associated with quitting. For every sustained quitter who develops Parkinson's that a persistent smoker would not have developed, many more sustained quitters are alive who would have died if they had kept smoking. The net health arithmetic strongly favors quitting.
Limitations
The data were self-reported, introducing the standard caveat about recall accuracy. The participants were predominantly Korean male smokers, and findings may not generalize to women or populations with different smoking patterns or genetic backgrounds. This study cannot explain why the inverse association between smoking and Parkinson's exists - only that it persists when changes in smoking status are tracked longitudinally. Identifying which components of cigarette smoke drive the reduced Parkinson's risk, and whether they could be delivered without tobacco's harms, is the research question these findings motivate but do not answer.