Short-term PM_2.5 air pollution and "deaths of despair" in Michigan, 2006-2016: a case-crossover study

Particulate matter is a known risk factor for cardiovascular and respiratory illness. Ecological analyses have indicated associations for mental health outcomes, but there has been only limited work on the impacts of individual exposure to air pollutants and mental health-related mortality. This research uses a novel case-crossover design to assess associations between short-term lag exposure to particulate matter 2.5 (PM_2.5) and mortality from suicide, alcohol-related liver failure and opioid drug overdose.

Records for all deaths from suicide, alcohol-related liver failure, and overdose were obtained from the Michigan Department of Health and Human Services (MDHHS) for the years 2006 to 2020. Residential addresses were geocoded, and latitude/longitude locations were added to the database. Gridded raster data of daily PM[Formula: see text] concentrations at 1km resolution were obtained from the CAFE Climate and Health Research Coordinating Center Collection. PM[Formula: see text] exposure for all 14 days preceding the recorded date of death was extracted for all decedents at each point. A case-crossover design was used, where everyone served as their own control, staggering exposure days on the same weekday in the same month of the date of death. Lag associations of PM[Formula: see text] and mortality were then tested using regression models stratified by race and sex within a distributed lag non-linear modelling framework, including the cross-basis for PM[Formula: see text] exposure.

There were 30,930 mental health-related deaths included in the dataset between 2006-2016. Among these, there were 13,336 suicides, 6,875 deaths from alcohol-related liver failure and 10,719 deaths from overdose. The mean PM_2.5 exposure was 9.65 micrograms per cubic meter. Patterns of association between time and exposure to PM[Formula: see text] differed between the types of mortality. While no association was statistically significant, exposure to extremely high levels of PM[Formula: see text] had a positive association with mortality from all three types of mortality at and around lag day 7, but not after. Seasonal analyses indicated that increasing exposure to high levels of PM[Formula: see text] was significantly associated with suicide in the Fall and Winter months. In the Summer, exposure to any amount of PM[Formula: see text] over the WHO recommended safe level up to two weeks was associated with increased risk for suicide mortality. Tests for effect modification by Black/white and binary sex groups did not indicate significant differences in mortality risk given exposure.

While we did not find overall statistically significant associations of PM[Formula: see text] exposure with mental health-related mortality, our results suggest that there might be possible associations of cumulative extreme levels of PM[Formula: see text] exposure over one week. As suicide, alcohol-related mortality and overdose are the end of a long cascade of events and factors, future work might test lag associations with non-fatal mental health-related episodes or assess individuals' exposure directly.