Long‐Term Wildfire Smoke Exposure and Incident Dementia in a Large California Cohort

Abstract Background Long‐term exposure to ambient air pollution–including fine particulate matter <2.5µm in diameter (PM 2.5 )–has previously been associated with incident dementia. As climate change drives longer and more intense wildfire seasons, exposure to PM 2.5 produced by wildfires may be a unique and increasingly important risk factor for dementia. Method In this retrospective open cohort study, we examined the association between long‐term exposure to wildfire PM 2.5 and dementia among Kaiser Permanente Southern California patients aged ≥60 from 2009‐2019 in California. Study participants were dementia‐free at baseline. Incident dementia was identified within the electronic health record using International Classification of Diseases 9 and 10 codes. Estimates for rolling three‐year average concentrations of wildfire and non‐wildfire PM 2.5 were assigned for each participant based on census tract of residence, which was updated quarterly. We used pooled logistic regression to estimate the odds of dementia diagnosis associated with a one µg/m 3 increase in the three‐year average of wildfire and non‐wildfire PM 2.5 . All models included fixed effects for calendar year and adjusted for age, sex, race and ethnicity, marital status, smoking status, Charlson Comorbidity Index (minus dementia), and census tract poverty and population density. Result The study included 1,227,241 members. Approximately half were women (53%) and were married (54%). A majority self‐identified as non‐Hispanic White (49%) or Hispanic (26%). Over the study period, the mean wildfire PM 2.5 concentration was 0.09 (IQR: 9.6‐12.4). After adjusting for covariates, the odds of dementia diagnosis was 10% higher for every 1 µg/m 3 higher three‐year average wildfire PM 2.5 concentration (OR = 1.10, 95%CI: 0.96,1.25). For non‐wildfire PM 2.5 the odds of dementia diagnosis was 1% higher for every 1 µg/m 3 higher three‐year average exposure (OR = 1.01, 95%CI: 1.00,1.01). Conclusion Long‐term exposure to PM 2.5 , both wildfire and non‐wildfire, may be an important risk factor for dementia.