The findings of a new study may explain why smokers are at lower risk of developing Parkinson’s disease than non-smokers.
Researchers followed 512,701 adults in China, including 1,131 people with Parkinson’s disease and 2,949 with other neurodegenerative diseases.
Smoking was assessed through self-reported frequency and measurements of carbon monoxide in participants’ breath, which is commonly used as an indicator of smoking.
The international research team found that both a history of smoking and higher levels of exhaled carbon monoxide were associated with a lower risk of Parkinson’s disease.
Smokers generally had higher carbon monoxide levels, but non-smokers with higher levels also had a lower Parkinson’s risk.
The researchers said this suggested carbon monoxide may independently protect against the disease and could help explain the previously observed association between smoking and a lower risk of Parkinson’s.
Associate Professor Andrea Bugarcic, from the National Center for Naturopathic Medicine at Southern Cross University, said: “This study demonstrates the power of longitudinal patient data.
“Using observational research methodology, this study investigated the risk of developing neurodegenerative diseases in a large but geographically focused sample.
“Combining what patients say about their lives, such as smoking and environment, with measurements we can make as scientists, such as exhaled CO, the study links higher exhaled CO to a lower risk of Parkinson’s disease only, not other causes of dementia.
“While increased exhaled CO is linked to smoking, the current study also points out that risk levels for nonsmoking and smoking patients are the same.
“Collectively, the study not only points out a possible mechanism for the previously observed protective effects of smoking on Parkinson’s disease risk, but it also reminds us that CO release is a larger environmental consideration.”
A 2026 South Korean cohort study of over 410,000 adults found persistent smokers had the lowest risk of Parkinson’s during a median 9.1-year follow-up, while people who quit smoking saw a 60 per cent higher risk of the disease compared with those who kept smoking.
This mirrors older research, including a large NIH-AARP study that found the risk of Parkinson’s fell the longer someone had smoked, dropping by around 41 per cent in those who had smoked 30 or more years, and a doctors’ cohort where current smokers had roughly a 40% lower Parkinson’s risk than those who had never smoked
Bugarcic said: “Despite the controversial outcomes and limitations of this study, my perspective is that researchers across the methodological spectrum should take on the challenge set out by this study, understand why and how exhaling more CO links specifically to lower Parkinson’s disease risk.
“As a scientist, my contribution would be understanding molecular puzzles using a precision medicine approach that can then lead to human studies on specific groups of patients.
“This is where studies like this matter, they give a voice to patients that then mobilises all that science has to offer, from understanding why to ensuring a grounded approach to therapeutic development.”
