Smart Science

Smokers have a 30% lower risk of Parkinson's. A new study finally found the cause. Researchers at the University of Oxford followed 512,701 adults in China for about 12 years and measured the carbon monoxide (CO) in their breath at the start. CO is the same gas found in cigarette smoke, but your body also makes tiny amounts of it, where it works as a signaling molecule. Over the follow-up, 1,131 people developed Parkinson's. Regular smokers had about a 30% lower risk, as earlier studies found. The surprise came from people who had never smoked: those with higher CO in their breath were roughly a third less likely to develop Parkinson's than those with the lowest levels. The link didn't show up for other brain diseases. Let's be very clear: smoking is never a way to prevent Parkinson's. It causes cancer, heart disease and stroke, and its harms far outweigh anything else. What this study offers is a clue. If low levels of CO really calm inflammation and cell stress in the brain, as lab and animal studies hint, scientists could one day design safe, controlled CO treatments. A first small trial of a low-dose CO drug in Parkinson's has already started at Harvard. This is an observational study, so it shows a link, not proof that CO protects the brain. source: Bueno Lopez, C., Iona, A., Turnbull, I., et al. (2026). Smoking, exhaled carbon monoxide, and risk of Parkinson disease. JAMA Neurology.