How Extreme Heat Can Influence Mood and Mental Health

“When we’re not comfortable, we’re not at our best,” said C. Munro Cullum, a clinical neuropsychologist at UT Southwestern Medical Center, in Dallas. The discomfort of heat, and the energy it takes for the body to cool down, can lower overall resilience. So agitation, irritation and pain become less bearable, he said.

Our bodies are also used to a certain baseline level of stress, said Dr. Martin Paulus, scientific director and president of the Laureate Institute for Brain Research in Tulsa, Okla., who worked with Dr. Obradovich on his 2018 study. When the body attempts to regulate its temperature during a heat wave, he said, it adds additional strain and results in more stress and inflammation. People with pre-existing mental health conditions may be especially vulnerable to the added heat stress, which can push their symptoms over the top, he said.

As for what’s happening in the brain during extreme heat, that’s challenging to study, Dr. Paulus said. In a lab, you can experiment with how the brain and the rest of the body withstand a few minutes or possibly hours of high temperatures, but you can’t do that for days, weeks or months at a time — and it’s those longer exposures that are really important for understanding how climate change may affect us in the long run.

But the fact that this link between heat and mental health is so consistent in people around the world suggests that the heat is doing something to the brain, Dr. Nori-Sarma said. Some researchers have hypothesized that heat may cause an imbalance in brain signaling or inflammation in the brain. But another prominent theory is that heat causes sleep disruptions, which in turn can worsen mental health symptoms.

Warm nights significantly worsen sleep, Dr. Obradovich said. “And we know from a large body of literature in psychology and psychiatry that insufficient sleep, sleep difficulties, and insomnia are very closely linked to worse mental health status over time.”

It’s possible that the explanation for heat’s effect on mental health may come from a combination of these different existing theories, Dr. Obradovich added.

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