The Effects of Heat and Air Pollution on Mental Health Related Mortality in California

Background: Higher ambient temperature and air pollution may play a role in increasing the risk of mental health related mortality; however, findings vary depending on study location. We examined the relationship between temperature and air pollution with deaths due to suicide and homicide in California—a region prone to high temperature and air pollution. Method: California death certificates from 2014 to 2019 were used to identify the deaths due to suicide and homicide. Residential data for decedents were used to assign exposure to daily temperature (maximum [Tmax], minimum [Tmin]) and daily average air pollution concentrations (particulate matter <10 µm [PM10] and <2.5 µm [PM2.5], nitrogen dioxide [NO2], ozone [O3]). A time-stratified case-crossover study design using conditional logistic regression was used to assess the effects of daily exposure to Tmax, Tmin, PM10, PM2.5, NO2, and O3 on suicide and homicide mortality, adjusting for relative humidity as a potential confounder. Two-exposure models pairing temperature with a single pollutant and interactions between temperature and air pollution were also explored. Results: We observed 24,250 deaths due to suicide and 10,148 deaths due to homicide. A 1-ºC increase in same-day Tmax and Tmin was associated with 0.44% (95% confidence interval, CI, 0.02%–0.90%) and 0.76% (95%CI, 0.17%–1.35%) increased odds of death due to suicide, respectively. The increased odds of homicide mortality per 1-ºC increase in same-day Tmax and Tmin were 0.86% (95%CI, 0.23%–1.50%) and 1.05% (95%CI, 0.15%–2.00%), respectively. Associations for air pollution were null. Tmax and Tmin associations were robust to the adjustment of each air pollutant. We found marginally significant interaction effects of minimum daily temperature with PM10 and O3. Conclusion: Our findings suggest that risk of suicide and homicide mortality increases with both increasing daily ambient maximum and minimum temperatures. Keywords: Temperature, Air pollution, Suicide, Homicide, Mortality