Smoking, Exhaled Carbon Monoxide, and Risk of Parkinson Disease.

Higher exhaled carbon monoxide among never-smokers in the China Kadoorie Biobank is linked to lower Parkinson disease risk, with a dose-dependent adjusted HR down to 0.65 (≥11.5 ppm).

• Why it matters: Smoking is epidemiologically associated with lower Parkinson disease risk, but the mechanism is unclear; clarifying whether exhaled CO relates to PD could explain that pattern.
• What they did: In a nationwide prospective cohort of 512,724 adults in China, measured exhaled CO was analyzed with Cox regression for first events, focusing on 675 never-smokers for PD outcomes.
• The result: Among never-smokers, exhaled CO showed broadly dose-dependent lower PD hazard (P for trend < .001) without associations for smoking-related diseases or other neurodegenerative diseases, supporting ongoing CO trials for PD.

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