Why Do Smokers Have A Lower Risk Of Parkinson’s Disease? – Expert Reaction

The study of over 500,000 Chinese adults found that those with more carbon monoxide in their breath were less likely to develop Parkinson’s disease over about 12 years of follow up, even if they had never smoked.

The SMC asked NZ experts to comment.

Professor Louise Parr-Brownlie (Ngāti Maniapoto, Te Arawa), Neuroscientist in the Department of Anatomy, University of Otago, comments:

“We’ve known for two decades that smoking tobacco reduces the risk of Parkinson’s disease by reducing inflammation in the brain. Lopez et al. (2026) reports that smoking reduced the risk of Parkinson’s disease by 30%, and this was weakly associated with carbon monoxide levels – the higher the level of carbon monoxide in expired breath, the more likely smoking protected for Parkinson’s disease. Carbon monoxide is produced when tobacco is burnt.

“Would I recommend that you smoke? No. Smoking significantly increases the risk of heart disease, stroke, lung cancer and other diseases.

“A dangerous interpretation from this study might be that increasing carbon monoxide exposure will prevent Parkinson’s disease. There is no evidence to support that – only an association was shown, not causation.

“Carbon monoxide is dangerous to your health! It replaces the oxygen carried by red blood cells, starving your brain and other tissues of oxygen, and can rapidly cause death.

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“The greatest protection for Parkinson’s disease is to age well. Less than 15% of people diagnosed with Parkinson’s have an underlying genetic cause. For the remaining 85%, a complex combination of environmental factors, such as exposure to heavy metals and pesticides, reduced quality sleep, lack of exercise and a diet containing a lot of fat, increase the risk of Parkinson’s disease. Many of these environmental factors can be managed.”

Conflict of interest statement: “No conflicts of interest.”

Dr Toni Pitcher, Senior Research Fellow in Parkinson’s epidemiology, University of Otago, Christchurch, comments:

“The so-called protective effects of cigarette smoking on Parkinson’s disease risk has sat uncomfortably with the medical community since it was first described in 1959. Surprisingly, the exact mechanism underlying this association remains elusive. Nicotine, perhaps the most obvious candidate to mediate the association has been studied widely, but no firm mechanisms for protection have been uncovered.

“The newly published paper by Lopez et. al. provides further evidence for another potential candidate mediating this association – carbon monoxide. This is the first large-scale demonstration that Parkinson’s is also less common in individuals with higher levels of exhaled carbon monoxide in the absence of a smoking history.

“Carbon monoxide has anti-inflammatory effects and in the brain helps to counteract cell stress. There is the potential that individuals with higher internal levels of carbon monoxide are more able to fight off inflammatory processes and better maintain brain health.

“The challenge now is to replicate these findings in independent cohorts and to better understand how carbon monoxide counteracts the pathology associated with Parkinson’s. Study authors refer to a registered clinical trial testing the safety of low-dose carbon monoxide in people with Parkinson’s, highlighting its therapeutic potential.

“Caution is needed however, we know there is no one cause of Parkinson’s and as such there is unlikely to be one ‘cure’ for all. Identifying who will benefit most from a particular therapy remains a challenge within the Parkinson’s field.”

Conflict of interest statement: “No conflicts of interest.”

Chris Bullen, Professor of Public Health Department of General Practice and Primary Care, School of Population Health, University of Auckland, comments:

“The finding that people who smoke have a lower risk of Parkinsons Disease (PD) has until recently been attributed to the effect of nicotine. However, this large well-conducted epidemiological study points instead to a role for carbon monoxide (CO), a gas found at higher levels in the exhaled breath and blood of people who smoke.

“The researchers surveyed and took samples from individuals from a cohort of more than half a million Chinese adults, many of whom (mostly men) were regular smokers. Their findings suggest that the inverse association between smoking and PD is not attributable to tobacco smoking itself but rather that CO exposure may contribute to this association.

“These findings point to the possibility that CO could play a role in PD treatment but more research is needed to explore this hypothesis. Importantly, the study counters the presumed protective effects of smoking on PD and adds to the case for continued efforts in tobacco control.”

Conflict of interest statement: “No conflict.”

Associate Professor George Laking, Department of Cancer Sciences, Faculty of Medical and Health Sciences, University of Auckland, comments:

“I can offer a parallel from oncology. Cigarette smoking appears to be mildly protective against some estrogen-related cancers (estrogen-receptor positive breast cancer, endometrial cancer, endometrioid and clear cell ovarian cancers, and thyroid cancer).

“We know that tobacco exposure is destructive to human tissues. Sometimes it might interfere with aspects of normal physiology that increase the risk of specific cancers. For example, smoking is toxic to the ovaries, and thereby a risk factor for early menopause. Lifetime exposure to ovarian estrogen is a risk factor for estrogen-receptor positive breast cancer. This could explain the apparent ‘protective’ effect of smoking for that illness.

“We know that smoking is overall harmful to brain health. Perhaps it is relatively more harmful to one of the physiological risk factors for Parkinson’s Disease. None of this changes the message that smoking is overall incredibly harmful to health. For example, early menopause comes at a cost of increased cardiovascular risk and mineral bone loss. And smoking increases the risk of estrogen-receptor negative breast cancers.”

Conflict of interest statement: “No conflicts to declare.”

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