Weather, air pollution, and migraine: a case-time series analysis examining environmental exposures and transient health outcomes recorded via smartphone application

BACKGROUND: Most studies of environmental exposures and migraine have been limited to weather or single-pollutant models and aggregate outcome measures. We estimated the associations between multiple environmental exposures and migraine events captured using a smartphone application (app) in the province of Ontario, Canada. METHODS: We obtained Ontario-wide local daily weather and pollution estimates for 2017-2019 from Environment and Climate Change Canada. The Migraine Buddy app team provided records from research-consenting users. Associations between environmental exposures and migraine attack onsets were examined with case-time series lagged multipollutant models, accounting for demographic and temporal covariates. RESULTS: We analyzed 69,808 migraine attacks reported by 7418 participants in Ontario, Canada. Overall cumulative estimates for 0-3 days suggested increased odds for migraine attacks with higher nitrogen dioxide (NO(2)) and ozone (O(3)), drops in barometric pressure, and cold winter temperatures. No association was observed for PM(2.5). Positive associations with NO(2) and O(3) were strongest 1 and 2 days after exposures, while associations with barometric pressure changes and cold winter temperatures were strongest on the first day. Estimates for warmer summer temperatures suggested a complex temporal pattern, with positive same-day association followed by 3 days of negative associations. CONCLUSION: This study presents a novel examination of the associations between air pollution and migraine attacks using small-area exposures, smartphone data, and the case-time series method. Onset of migraine was associated with higher NO(2) and O(3), colder winter weather, and positive and negative changes in barometric pressure