Research Aims: More than 47,000 individuals died by suicide and more than 312,000 received care in the emergency department (ED) for self-harm injuries in 2018. Recent research has associated mental health and suicide with air pollution and rising temperatures, but much less is known about this relationship with seasonal pollen. We propose to use newly available, high-frequency data to quantify the impact of seasonal pollen on mental health and suicides in the US.
Hypotheses: We hypothesize that increases in daily pollen levels are associated with increases suicides and visits to ED for mental healthcare.
Sample: We bring together novel and remarkably detailed data for 2006-2017: all-cause detailed mortality data from over 446,330 suicides in the National Vital Statistics System; health insurance claims for over 18 million individuals insured by UnitedHealthcare; daily pollen measurements for 33 urban localities collected by the National Allergy Bureau. We propose to use geospatial interpolation to extend these pollen measurements from urban to nearby rural areas.
Measures: The independent variable is daily pollen measured in parts per cubic meter. We aggregate suicides and visits to the ED to each locality to daily counts of each. While suicides are identified in mortality records, we use ICD-9 and ICD-10 diagnostic codes to define mental health care in the ED such as intentional self-harm (X710-X838) and suicide attempt (T1491).
Analyses and Procedures: To account for the relatively low count of suicides and mental health visits we will estimate a Poisson model of daily counts of these outcomes on daily pollen measurements. Our previous research informs us that pollen has a non-linear impact on health, which we model using quartiles of pollen levels. Pollen is significantly autocorrelated across time, which we model using concurrent and one-day lag of pollen, and include a seven-day moving average of pollen. All analyses will include daily weather, such as temperature and precipitation, and location and time fixed effects. We will repeat analyses by rural/urban location, age, gender, and race.
Potential Impact: Global warming is increasing the duration and intensity of the pollen season. Contrary to environmental pollution, leveraging policy to control pollen is neither possible nor desirable, as it is a naturally occurring effect of expanding green spaces. Policy, however, can and should mitigate the impact of pollen on the mental health within communities. This study would motivate national collection of pollen measurements, akin to pollutants, effective communication with medical providers and the public about rising pollen levels, and targeted seasonal outreach to vulnerable populations.
Next Steps: We will study the interactions of pollen with a wider set of local factors which contribute towards suicidality such as gun availability and access to mental healthcare. We will expand the definition of suicide to account for geographically clustered underreporting. We will also examine the relationship between pollen and use of alcohol and drugs, as both are known contributors to suicide and may be underreported. Finally, we will explore role of social determinants of health in the impact of pollen on mental health and suicide.
