Study Quantifies Environmental Stressors’ Impact on Human Mental Health in the US

By David Richards

Overlaying meteorological data with national-level health data, researchers reported that climate and meteorological stressors are associated with worsened mental health among U.S. adults. The research used an innovative approach to combine historical data to support that exposures to weather extremes, including weather-related disasters, and prolonged temperatures changes, all effects associated with climate change, pose a threat to overall health and well-being. The study, Empirical Evidence of Mental Health Risks Posed by Climate Change, led by Nick Obradovich, Ph.D., senior research scientist at the Max Planck Institute for Human Development in the Center for Humans and Machines, was recently named the 2019 Best Environmental Epidemiology Paper (BEEP) Award winner by the International Society for Environmental Epidemiology (ISEE).

NIEHS Grantee Paper Named Runner Up

Prenatal Exposure to DDT and Pyrethroids for Malaria Control and Child Neurodevelopment: The VHEMBE Cohort, South Africa,” a publication by NIEHS funded researchers, was recently named Runner Up for the Best Environmental Epidemiology Paper (BEEP) Award at ISEE 2019. This paper was published in the April 2018 issue of Environmental Health Perspectives.

In their paper, Eskenazi et al. describe their analysis of prenatal pesticide exposures and neurodevelopment at ages 1 and 2 years. Participants included 705 mother–child pairs enrolled in the Venda Health Examination of Mothers, Babies and the Environment (VHEMBE) birth cohort. This cohort, which was established in 2012, includes individuals from eight villages in the malaria-endemic Limpopo Province, South Africa. Half of the villages regularly sprayed DDT or pyrethroid pesticides indoors to kill mosquitoes. At 1 year of age, estimated prenatal exposure to DDT/DDE was not associated with differences in average scores on a standardized instrument used to measure neurodevelopment, after controlling for poverty, malaria status, and nutritional status. In contrast, pyrethroid exposure measured in the peripartum period was associated with lower social-emotional and language development scores at age 2.

“You and I are both being affected by the temperature we are being exposed to right now,” Obradovich said. “We are being affected by whether the sun is shining or by whether or not it is raining, and all of those effects likely accumulate over time. We wanted to turn our lens onto the day-to-day effects, and we saw that most of the stressors associated with climate change do positively correlate with a person’s mental health outcomes.”

Climate change is likely to amplify environmental stressors such as temperature variation, multiyear warming, and intensity and frequency of natural disasters, contributing to adverse environmental conditions for human populations. These types of conditions have already begun to show a relationship to negative mental health outcomes. Exposure to extreme weather events, such as hurricanes and floods, is associated with acute depression and post-traumatic stress disorder, and exposure to heat and drought increases the risk of suicide. However, quantifying less extreme population-level impacts has been difficult.

National-Level Meteorological and Health Datasets

Researchers looked at the Centers for Diseases Control and Prevention’s (CDC) Behavioral Risk Factor Surveillance System (BRFSS) data from 2002 to 2012 to study the individual’s mental health based on the self-reported number of days the respondent felt in a state of poor mental health. They juxtaposed those responses with meteorological data from NASA’s Earth Exchange and Oregon State University’s PRISM Climate Group from the same years to determine the weather conditions at the time and location of the questionnaire. They examined three types of environmental stressors, all of which are projected to become more frequent or severe with climate change: short-run extreme weather exposure measured as average consecutive days of excessive heat or precipitation, multiyear warming, and natural disaster exposure in the case of Hurricane Katrina in August 2005.

“We had this robust dataset of a couple million randomly selected U.S. citizens over the course of a decade that had said over the last 30 days ‘I had this many days of mental health problems’, and then we could map in the climate and weather data onto those responses,” Obradovich added. “It was very fortunate that the CDC asked that question for as long as they did.”

Controlling for social and economic determinants of mental health, the results found an increase in the prevalence of mental health issues in response to each of the three stressors. Average monthly temperature changes from under 30 degrees Celsius (86 degrees Fahrenheit) to greater than 30 degrees Celsius correlated to a 0.5% increase in mental health difficulties. Multiyear warming of one degree Celsius (1.8 degrees Fahrenheit) increase in average maximum temperatures associated with a 2% increase, and exposure to Hurricane Katrina linked to a 4% increase in reported mental health difficulties.

Climate Change and Mental Health

While the researchers recognize limitations in the BRFSS dataset, most notably that the information is self-reported and does not follow individuals over time, their findings suggest the need for further investigation of the associations between climate change and mental health. By aggregating micro-scale climate effects and self-reported mental health, the researchers have provided a quantitative estimate of the degree to which these environmental stressors, which will be exacerbated by the effects of climate change, are affecting mental health.

Moving forward, the researchers hope to build on their findings. “We are dealing with huge uncertainties,” Obradovich emphasized. “We are looking at historical relationships between weather and people’s well-being. One has to make a big assumption that that relationship will persist into the future and that climate change will have the precise effects that we project it does. That said, we are also coming up on a future that is very uncertain, so we have to do the research and use the best data that we have to figure out what we can do about it.”

Citation: Obradovich N, Migliorini R, Paulus MP, Rahwan I. 2018. “Empirical evidence of mental health risks posed by climate change.” Proceedings of the National Academy of Sciences 115.43 (2018): 10953-10958.