Suicide rates in the U.S. have been steadily rising since the late 1990s, leading to an urgent need to understand what\u2019s putting people at risk. Risk factors include high air pollution and hot temperatures, which have each been individually associated with increased suicide risk in the days after exposure.<\/p>\n
Now, a new study has found that, in the hot summer months, high levels of air pollution can make unusually hot days much riskier.<\/p>\n
\u201cThe two-week period just before suicide is a critical time for intervention, so we\u2019re really trying to understand what\u2019s happening in that really short-term period,\u201d says Amanda Bakian, PhD,<\/a> research associate professor of psychiatry at University of Utah Health, Huntsman Mental Health Institute investigator, and the senior author on the study. \u201cMany environmental factors have been associated with short-term suicide risk, but very little has been done to consider what\u2019s happening in a mixture.\u201d<\/p>\n The results are published in Environment International<\/a>.<\/p>\n Higher temperatures, higher risk<\/p>\n Heat stress alone is associated with higher suicide risk all year round, but especially during the warmer months, the study found.<\/p>\n The researchers analyzed over 7,500 suicide cases across Utah from 2000\u20132016, cross-referencing the approximate levels of heat stress, nitrogen dioxide, and fine particulate air pollution at the decedent\u2019s address. While previous studies had looked at temperature alone, this study used a measure of heat stress called wet bulb globe temperature, which includes wind speed, humidity, and cloud cover to determine a more accurate measure of how heat actually affects the body.<\/p>\n Heat exposure was associated with higher risk of suicide. For every 9\u00b0F increase in wet bulb globe temperature, the risk of suicide increased by 5%. The risk was especially amplified during the warmer periods of the year, from late March to late September.<\/p>\n Air pollution makes hot days more dangerous<\/p>\n For an air pollutant called nitrogen dioxide, produced at high levels by fossil fuel power plants and gas-powered vehicles, the story is more complicated. \u201cWe found a strong synergistic effect of heat and nitrogen dioxide, which is one of the traffic-related air pollutants, particularly during the warm season,\u201d says Dirga Lamichhane, PhD,<\/a> postdoctoral researcher at U of U Health and first author on the study. \u201cThe effect of heat stress is especially high when the NO2 level is very high.\u201d<\/p>\n In other words, during the warm season, nitrogen dioxide on its own isn\u2019t associated with higher risk of suicide\u2014but higher levels of nitrogen dioxide can amplify the risk associated with wet bulb globe temperature. During the warm season, if levels of nitrogen dioxide are high, every 9\u00b0F increase in wet bulb globe temperature is associated with a nearly 50% increase in suicide risk.<\/p>\n During the cold season, when air pollution tends to be much worse overall in Utah, high levels of nitrogen dioxide are associated with higher suicide risk regardless of temperature.<\/p>\n Understanding risk to improve interventions<\/p>\n The researchers emphasize that the links between heat stress, air pollution, and suicide are only associations\u2014they don\u2019t know whether these environmental conditions directly cause increases in risk.<\/p>\n As the climate shifts, these patterns of risk could change in unexpected ways, requiring further study. \u201cThis data was collected between 2000 and 2016,\u201d Bakian explains. \u201cSince then, we\u2019ve seen the advent of wildfire season in Utah, so that could potentially change nitrogen dioxide and fine particulate matter measures in the summertime. Now that there\u2019s more seasonal variability in air pollution in Utah, that raises questions about what that synergism with high temperatures looks like.\u201d<\/p>\n In other future work, the researchers hope to help figure out who\u2019s most vulnerable to environmental changes by investigating how genetic risk factors for suicide may interact with environmental factors.<\/p>\n \u201cFuture studies could link environmental data with genetic markers to see the interaction between temperature and some of the genetic factors and see the contribution of each factor to suicide risk,\u201d Lamichhane says. \u201cThis may really help to understand and predict suicide.\u201d<\/p>\n The authors add that, while air quality and heat interventions historically haven\u2019t been considered in the context of suicide prevention, their results suggest that environmental policies could help prevent suicide. And better prediction of who is at risk for suicide and when could enable just-in-time interventions to save lives.<\/p>\n ###<\/p>\n Do you need help? Call 988<\/a> to reach a free, confidential 24\/7 support line for suicidal crisis or emotional distress. The Huntsman Mental Health Institute Crisis Care Center<\/a> also offers 24\/7 walk-in mental health services for adults. Additional information and assistance can be found through the Utah Chapter of the American Foundation for Suicide Prevention<\/a>.<\/p>\n Are you concerned about a loved one or friend? Asking is the single most effective intervention for suicide. Learn how to help.<\/a><\/p>\n ###<\/p>\n