Regular smoking was associated with a lower risk of Parkinson disease (PD), and among people who never smoked, higher levels of exhaled carbon monoxide (CO) were associated with a lower risk of PD in a broadly dose-dependent manner. This nationwide prospective cohort study included 512,724 adults aged 30–79 years from the China Kadoorie Biobank and followed participants for approximately 12 years, during which 1,131 cases of PD and 2,949 cases of other neurodegenerative diseases were recorded. Regular smoking was associated with increased risks of lung cancer, ischemic heart disease, stroke, and all-cause mortality, but a lower risk of PD (adjusted HR, 0.70). Among never smokers, compared with exhaled CO levels below 2.0 ppm, PD risk was lower at 2.0–<3.0 ppm (HR, 0.85), 3.0–<5.0 ppm (HR, 0.62), 5.0–<11.5 ppm (HR, 0.68), and ≥11.5 ppm (HR, 0.65), with a significant trend (P<.001); these associations were more pronounced in women and were not observed for smoking-related diseases or other neurodegenerative diseases. Similar associations between exhaled CO and PD were also found among regular smokers. The findings suggest that CO may have a potentially protective role in the development of PD, helping to explain the epidemiologic association between smoking and lower PD risk and supporting ongoing clinical trials investigating CO as a potential treatment for PD. Source: https://jamanetwork.com/
