• Smoking history and exhaled carbon monoxide levels are both associated with a lower risk of developing Parkinson’s disease.
• In a new study, researchers set out to better understand this link. They found that participants who had not smoked but had high exhaled carbon monoxide levels also had lower risk of Parkinson’s disease.
• Having higher exhaled carbon monoxide levels was not linked to a lower risk of other neurodegenerative diseases.

A new study may have shed some light on the peculiar association between smoking and a lower risk of developing Parkinson’s disease.

The study, published in JAMA Neurology, reports that exposure to carbon monoxide may contribute to this link.

Parkinson’s disease is a brain condition that is growing increasingly common. The World Health Organization (WHO) estimates that its prevalence has doubled in the past 25 years.

The disease causes damage to nerve cells in an area of the brain called the substantia nigra, resulting in symptoms such as tremors and coordination problems. Some people with Parkinson’s go on to develop dementia over time.

Experts are unsure what causes Parkinson’s at present, but believe that genetic changes or environmental exposures may play a role.

Smoking cigarettes does not actually improve Parkinson’s

Previous population studies have noticed a lower risk of Parkinson’s disease among people who smoke.

While studies in rodent models led researchers to suggest that nicotine might have some kind of protective effect, a recent randomized clinical trial found that nicotine therapy provided no benefit to people with Parkinson’s. In fact, the trial suggested the nicotine may have even made their symptoms worse.

Other studies in cells and animals have suggested that carbon monoxide, another by-product of smoking, might also play a protective role.

As a result, an international team of researchers set out to see how carbon monoxide exposure might relate to the risk of Parkinson’s disease.

The researchers examined data from 512,701 participants in the China Kadoorie Biobank, a cohort coming from 10 different urban and rural areas within China. The participants had a mean average of 52 years at the beginning of the study.

Participants provided information about their smoking history along with other aspects of their lifestyle and medical history via questionnaires. Clinicians also measured the amount of carbon monoxide they exhaled.

The researchers examined the health outcomes of the participants over a follow-up period of 12 years. During this time, they noted a total of 1,131 people developing Parkinson’s disease and 2,949 developing other forms of neurodegenerative disease.

They then looked to see if there were any patterns between these health outcomes, smoking histories, and measurements of exhaled carbon monoxide taken at the beginning of the study period.