Hot, polluted days can raise suicide risk by nearly 50%. Researchers don't know exactly why

It’s already hot in the Valley of the Sun this spring — we’ve been breaking temperature records back to back — after living through the hottest winter on record.

And research shows the heat combined with high pollution levels can lead to an increased suicide risk.

Amanda Bakian, Ph.D., is a research associate professor of psychiatry at the University of Utah’s Huntsman Mental Health Institute — and, she told The Show, suicide rates in the United States have gone up 30% over the past 30 years — even as we’ve worked to prevent it.

So there’s a big need to understand what’s happening in the short term just before a suicide happens.

Amanda Bakian

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Handout

Full conversation

AMANDA BAKIAN: We do have an understanding of some of these more critical risk factors for suicide risk in the short term. You know, right now we know that they may include something like insomnia, so not sleeping well, something like, you know, substance use, something like a major life event.

That's clearly not enough to prevent suicide deaths. So I felt as a suicide prevention researcher that we needed to expand the type of influences that might be associated with suicide risk.

LAUREN GILGER: Right. So what led you to air pollution and heat? Like, are those things that made sense to you as a researcher that might be part of this equation?

BAKIAN: Well, about 15 years or so ago, at that point, there was a fair bit of research that actually had established a causal relationship between poor air quality and the risk of physical health outcomes such as cardiovascular disease and respiratory disease. And living in Salt Lake City, Utah, in the wintertime, we would often experience wintertime air inversion events that trap in air pollutants.

And so talking with colleagues, we would look at these wintertime smog events in Salt Lake City and wonder, could these events be related to other health outcomes? And in Utah, Utah currently has among the highest age-adjusted suicide rates in the nation. So we thought, well, this may be something that's somewhat unique to Utah. Not entirely, but a little bit unique. There isn't much research on the relationship between poor air quality and suicide risk.

We decided to do one of the first studies and certainly the first U.S.-based study to look at the relationship between short term ambient air pollution and the risk of suicide. And we did find a relationship between short term nitrogen dioxide and short term fine particulate matter exposure and the risk of suicide.

So based on that work, the next thing we considered was the fact that we are not exposed to one single air pollutant at a time. We are exposed to a mixture of exposures. And these include not only air pollutants, but also weather factors that have also been found be associated with suicide risk, such as heat, such as solar radiation and such as precipitation.

So at that time we knew we had to expand this work to consider components of a mixture and see if we could try to figure out how these components may be working together as well as individually to influence suicide risk.

GILGER: OK, so tell us what you found. You did see suicide risks jump when you saw short term heat stress and air pollution by how much?

BAKIAN: First thing we did was replicate the work from our prior study, which we felt was really important. So we found that independently the air pollutants, short term exposure to them was associated with suicide risk when we considered suicide deaths across Utah for a larger period of time. And then we considered, we measured how they may work together in the context of heat.

So what we first established was an association between increasing heat and risk of suicide. Then when that heat is in the presence of high levels of air pollution like nitrogen dioxide, then we see the effects of heat amplified, so that we see increase in the relative risk of suicide to be about a 50% increase in that risk.

GILGER: So what do you think is happening here? Do you think this is something like mental health wise in terms of being stuck inside or isolated because of the heat? I know heat makes people angry. We've talked about that before. Or is it something that's more physiological?

BAKIAN: Yeah, so that's a great question. In terms of the mechanism that might underlie this relationship, that is one where we need additional follow up work. We have some hypotheses about what might be going on. The first is absolutely there could be some behavioral changes that are made in the short term. When it gets hot, it may force us inside.

It may mean that we get less physical activity, we may get less social interaction. All of these components that are really protective in terms of suicide risk. It may be the exposure itself. We know that heat and high temperatures can really stress us out physically. It can activate our HPA (Hypothalamic-Pituitary-Adrenal) Axis system and potentially that plays a role.

In addition, because we're seeing this interaction or these combined effects of air pollution and heat, you know, it may be the same biological processes that are, you know, implicated following those disease exposures, or it may be multiple biological processes. And that might be why we see the amplification of the impacts of these two exposures.

Because when we think about air pollution exposure, the mechanisms that we, we think are implicated there are inflammation or oxidative stress or hypoxia, where our oxygen saturation gets reduced. So, so yeah, there are quite a few biological mechanisms that could be involved.

GILGER: Super interesting, super interesting. So I mean, does this kind of play out in terms, if you look at, you know, heat and hot parts of the country or high pollution parts of the country and suicide rates? Like I know we have, we tend to have higher suicide rates here in Maricopa County than we do on a national average.

BAKIAN: Yeah. So one thing that's been interesting that I think just sort of corroborates our findings in this study is that historically in temperate regions of the world, we have found peak suicide rates to take place in the late spring to early summer. We're starting to see evidence of a shift of those peak rates towards the hottest part of the summer.

GILGER: Yeah, interesting. So let me ask you lastly then, Dr. Bakian, you said, you know, intervention is something that you're stressing here. Like what does this research show you or tell you or teach us about what we might be able to do to try to prevent suicide?

BAKIAN: I think it's telling us a number of different things. I think just like we are trying to do when it comes to an lot of health outcomes, which is to personalize our care, personalize our interventions, because we are so very different as people, we're really, really complex and heterogeneous. So one solution does not fit all.

So by broadening our understanding of short term risk factors for suicide, one of our next steps is to try to understand who is most vulnerable to these exposures. When we can understand who's highly sensitive to increased heat, to poor air quality when it comes to their suicide risk, well, then we can more personalize the interventions we have available that are related to suicide and to suicide prevention in the short term.