July 2022 was one of the hottest months on record, according to the National Oceanic and Atmospheric Administration. It was the sixth-hottest July since the U.S. began recording temperatures, 143 years ago. In addition, overnight temperatures in the month hit their highest levels in recorded history.
These warmer temperatures lead to all sorts of implications—melting glaciers, challenges for farmers, and effects on wildlife to name a few. It may surprise you to learn that these higher temperatures also have detrimental effects on our mental health.
A systematic review published last summer in the journal Environment International lays out the evidence on heat exposure and mental health outcomes; it combines data from 53 studies that examined hospital records during heatwaves. Researchers found significant increases in hospital and emergency visits due to mental health problems and in deaths due to mental health conditions during heatwaves. Specifically, mental health deaths increase by 2 percent every time the temperature increases by 1 degree Celsius.
Extreme heat is most likely to contribute to mental health problems related to substance abuse and cognitive impairments, such as dementia. Deaths from pre-existing psychiatric illnesses triple compared to other pre-existing conditions during heatwaves. The risk of suicide also increases as the temperatures rise.
Older people face the highest risk of mental health problems during heatwaves, most likely because their bodies are less capable of handling stress. People living in tropical and sub-tropical climate zones are also at higher risk.
A more recent study, published in February in JAMA Psychiatry, found an 8 percent increase in emergency department visits for mental health problems on the hottest days of the year compared to the coolest days. People are more likely to come to the hospital for self-harm, substance use, anxiety, and mood disorders as temperatures increase, the study found.
What’s going on here? Medical experts don’t exactly know, but there is some evidence that higher temperatures affect brain chemicals—specifically serotonin and dopamine levels—that help to regulate mood, cognitive function, and our ability to perform complex tasks. Higher temperatures also lead to irritability and psychological distress, which are contributing factors to substance abuse and suicide. There is also clear evidence that exposure to high temperatures negatively impacts cognitive function, which likely explains the increased hospitalizations for dementia.
Extremely hot weather also disrupts sleep. Sleeping problems are linked to nearly all mental health problems, and also lead to irritability, frustration, and poor mood. This is why higher overnight temperatures pose a serious threat to our mental health.
The take-home message: The sweeping effects of climate change extend to our mental health. Finding a way to keep cool, especially at night while sleeping, is important, particularly for people at higher risk for developing mental health problems or those with pre-existing mental health disorders.
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