Nikhil Prasad Fact checked by:Thailand Medical News Team Sep 13, 2026 1 hour, 15 minutes ago
A massive study involving more than half a million adults has uncovered a surprising link between carbon monoxide and Parkinson’s disease. Researchers found that people with higher levels of carbon monoxide in their exhaled breath were less likely to develop Parkinson’s, raising intriguing questions about whether carefully controlled low doses of the gas could eventually have therapeutic potential.
A major study involving more than half a million adults found that higher exhaled carbon monoxide levels were associated
with a lower risk of developing Parkinson’s disease
Carbon monoxide, or CO, is best known as a poisonous gas that can cause serious illness or death at high concentrations. However, the human body also naturally produces tiny amounts of CO, where it can act as a signaling molecule involved in inflammation, protection against cellular damage, and other biological processes.
The new findings could also provide an important clue to a long-standing medical mystery: why numerous studies have found lower rates of Parkinson’s disease among cigarette smokers.
A Study Involving More Than Half a Million Adults
Researchers analyzed data from 512,701 adults enrolled in the China Kadoorie Biobank, one of the world’s largest long-term population studies.
Participants were recruited from 10 geographically diverse regions of China between 2004 and 2008. Their average age was approximately 52 years, and around 59% were women.
Researchers collected detailed information about smoking habits and measured carbon monoxide in participants’ exhaled breath. Exhaled CO provides an indication of recent exposure to the gas, including exposure from cigarette smoking.
Participants were then followed for approximately 12 years using health insurance information and disease and death registries. During follow-up, researchers identified 1,131 cases of Parkinson’s disease.
Smokers Had Higher CO and Lower Parkinson’s Risk
The researchers confirmed an observation that has puzzled scientists for decades.
Regular smokers had substantially higher concentrations of exhaled carbon monoxide and about a 30% lower risk of developing Parkinson’s disease compared with people who did not regularly smoke.
Average exhaled CO concentrations among regular smokers were approximately 11.1 parts per million, compared with only 3.5 parts per million among people who had never smoked.
Importantly, the findings do not mean smoking should be considered protective or recommended for Parkinson’s prevention. Smoking remained associated with increased risks of lung cancer, heart disease, stroke, and premature death.
Instead, researchers wanted to determine whether one particular component associated with cigarette smoke—carbon monoxide—might partly explain the unusual relationship between smoking and Parkinson’s.
Never-Smokers Provided the Most Important Clue
One of the strongest findings came from participants who had never smoked.
Amon
g these individuals, higher exhaled CO concentrations were also associated with progressively lower Parkinson’s risk. This suggests that the relationship cannot simply be explained by smoking.
Compared with never-smokers whose exhaled CO levels were below 2 parts per million, those with levels between 2 and below 3 ppm had roughly a 15% lower relative risk of Parkinson’s.
Participants with levels between 3 and below 5 ppm had approximately a 38% lower relative risk, while those between 5 and below 11.5 ppm had around a 32% lower risk. Those with CO concentrations of at least 11.5 ppm had approximately a 35% lower risk.
The overall pattern showed a significant relationship between increasing CO levels and decreasing Parkinson’s risk.
This
Thailand Medical News report notes that researchers attempted to account for possible environmental sources of CO, including passive cigarette smoke and indoor burning of coal or wood.
Women Showed an Especially Interesting Association
The relationship between higher exhaled CO and lower Parkinson’s risk appeared particularly pronounced among women who had never smoked.
This was noteworthy because smoking patterns differed dramatically between men and women in the study. More than two-thirds of male participants regularly smoked, compared with only around 2% to 3% of women.
Researchers suggested that biological differences between men and women in the body’s natural production or processing of carbon monoxide might potentially contribute to the difference. However, further studies are needed before scientists can determine why this sex-related pattern occurred.
Why Carbon Monoxide Could Affect the Brain
Although CO is dangerous at high concentrations, small amounts are naturally produced inside the human body.
At these very low levels, CO can participate in biological processes involving inflammation, oxidative stress, immune responses, blood vessel function, and mechanisms controlling whether damaged cells survive or die.
These processes are potentially important because Parkinson’s disease involves the progressive degeneration of nerve cells that produce dopamine, a chemical messenger essential for controlling movement and several other functions.
Previous laboratory and animal experiments have suggested that low-dose CO exposure may reduce inflammation and cellular damage under certain conditions.
The new human findings therefore provide additional justification for investigating whether controlled CO-related treatments could influence Parkinson’s disease.
Effect Appeared Relatively Specific to Parkinson’s
Another important observation was what researchers did not find. Among never-smokers, higher exhaled CO was not associated with increased risks of major smoking-related diseases such as lung cancer, ischemic heart disease, or stroke. Researchers also found no comparable protective association for most other neurodegenerative diseases examined.
This relative specificity strengthens interest in understanding whether CO could be affecting biological pathways particularly relevant to Parkinson’s.
Researchers From China and The United Kingdom
The researchers were affiliated with the Nuffield Department of Population Health at the University of Oxford, Health Data Research UK Oxford, Peking University Center for Public Health and Epidemic Preparedness & Response, Peking University Health Science Center, the Key Laboratory of Epidemiology of Major Diseases at Peking University, the Tongxiang Center for Disease Control and Prevention, and the China National Center for Food Safety Risk Assessment.
Could CO Eventually Become a Treatment?
The findings are particularly interesting because researchers are already exploring controlled low-dose carbon monoxide as a possible therapeutic strategy.
A Phase 2a clinical trial is evaluating an oral low-dose CO product in people with Parkinson’s disease. Such treatment would be fundamentally different from breathing cigarette smoke or exposing someone to dangerous environmental CO concentrations.
However, the current study cannot prove that carbon monoxide itself prevents Parkinson’s. Researchers could not completely distinguish CO naturally produced inside the body from environmental exposure, and exhaled CO was measured at baseline rather than continuously throughout follow-up.
The results will also need to be reproduced in other populations.
Conclusion
The findings provide important human evidence that higher carbon monoxide levels are associated with a lower risk of Parkinson’s disease, including among people who have never smoked. While this does not establish that CO directly prevents Parkinson’s, it offers a plausible new explanation for the long-observed association between smoking and lower Parkinson’s rates. Carefully controlled research will now be needed to determine whether low-dose CO can safely protect vulnerable brain cells and whether this unusual biological pathway can ultimately be transformed into a practical treatment without the severe health risks associated with smoking or carbon monoxide poisoning.
The study findings were published in the peer reviewed journal: JAMA Neurology.
https://jamanetwork.com/journals/jamaneurology/article-abstract/2853696
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