Air pollution and mortality in a University of Michigan amyotrophic lateral sclerosis cohort: a survival analysis

BACKGROUND: Amyotrophic lateral sclerosis (ALS) is a rare, fatal, neurodegenerative disease. With limited treatment options, identifying modifiable risk factors that impact ALS survival is an important goal. Air pollution may be one such risk factor, yet the research on this topic is limited. METHODS: We assessed survival for ALS patients at the University of Michigan Pranger ALS Clinic who were recruited to participate in a prospective cohort study between 2009 and 2022. Participants’ personal characteristics were linked with residential air pollutant levels of fine particulate matter mass (PM2.5), nitrogen dioxide (NO2), and ozone (O3), as well as several particle components, including black carbon (BC), nitrate, sulfate, and sea-salt (as a negative control) over follow-up. To assess the role of air pollution on ALS mortality we used time-dependent Cox proportional hazards models with days from diagnosis as the time axis, adjusted for potential confounders and co-pollutants. RESULTS: Across the 1,276 total years of person-time during follow-up (2.7 ± 2.5 years per participant) there were 329 deaths. In fully adjusted multi-pollutant models, one interquartile range (IQR) (2.1 µg/m3) higher 1-year average PM2.5 was associated with a 66% (HR 1.66 per IQR; 95% CI 1.03–2.68) increase in the hazard of death. The other pollutants were not associated with death in participants with ALS . CONCLUSIONS: This finding suggests a seven month longer median survival for a 2.1 µg/m3 decrease in 1-year average PM2.5, which is significant given that ALS lacks a cure and that existing treatments only extend survival by a few months.