Parkinson's: why smokers appear to have a lower risk – researchers' new explanation

For several years, researchers have been intrigued by a statistical observation: people who smoke appear to have a lower risk of developing Parkinson's disease than those who have never smoked. A new study proposes a possible explanation linked to carbon monoxide, though specialists stress that this does not mean smoking carries any health benefit, according to Newsweek.

A study involving over 500,000 people

Researchers from the United Kingdom and China examined the link between exhaled carbon monoxide levels and the risk of Parkinson's disease in a study published in JAMA Neurology, which included over 500,000 participants.

A notable finding was observed among people who had never smoked: those with exhaled carbon monoxide levels of at least 3 ppm (parts per million) showed a roughly 30% lower risk of Parkinson's disease.

The researchers note that this result does not prove that carbon monoxide prevents the disease, but rather offers a new avenue for investigating the biological mechanisms involved. Carbon monoxide is best known as a toxic gas; however, the human body also produces it in small quantities, and at low concentrations it may act as a signalling molecule, with possible effects on inflammation, oxidative stress, and cell survival.

An association observed for decades

The link between smoking and a lower risk of Parkinson's disease is not new. A study that followed over 30,000 British doctors over a period of 65 years showed a 30–40% lower risk among smokers compared with people who had never smoked.

Researchers have also explored other possible explanations:

• Studies on smokeless tobacco products have identified similar associations, suggesting that certain compounds found in tobacco leaves — rather than smoke itself — may influence neurological mechanisms.
• Nicotine is another hypothesis under investigation, as it interacts with receptors involved in the brain's dopamine circuits and may have effects on inflammation and the functioning of dopamine-producing cells.

Not a reason to smoke

Specialists are clear in their warning that this statistical association does not make cigarettes a means of protection against Parkinson's disease. Smoking remains linked to serious health risks, including cancer, cardiovascular disease, stroke, and lung conditions.

The aim of this research is to identify the precise mechanism behind the observed association and, potentially, to isolate a beneficial biological effect that could be achieved without exposure to the harmful substances in tobacco or to dangerous concentrations of carbon monoxide.

Parkinson's disease is a progressive neurodegenerative condition that primarily affects movement and is caused by the deterioration of nerve cells involved in dopamine production. Researchers hope that a better understanding of this unusual relationship observed in smokers may, in time, open new avenues for preventing or slowing the progression of the disease.