Humans can survive only in a relatively narrow range of temperatures. We have learned how to cope with the cold but have fewer options when it is hot. Heat is harmful to us. The ideal temperature for humans is around 71-72 F (our tolerance limit is about 108 F). High temperatures cause serious health problems, including heat exhaustion, heat stroke, heart attacks, and cerebrovascular accidents. Children are the most vulnerable, as are the socioeconomically disadvantaged.
It shouldn’t surprise us that heat also affects our mental health. Most of us feel bad when it is too hot, and it is for good reason. Psychological reactions to sustained high heat can range from simple stress to clinical disorders. Substance and alcohol use increase during hot periods. Aggressive behaviors increase as well, which may reflect the fact that not only are people hotter but they are more likely to be outdoors and among crowds. Other types of violence, such as violent crime and domestic abuse, also increase during hotter months.
The heat is particularly challenging for people with mental disorders. Most disorders worsen during heat waves, including mood, anxiety, and psychotic disorders. There is also an increase in psychiatric hospitalizations during periods of extreme heat. One study found that for every 1 degree C (1.8 F) increase in five-year warming, there was a 2 percent increase in the prevalence of mental health disorders.
Most concerning is the risk of completed suicides, which increases during heat waves. One meta-analysis of 14 studies found that for every 1 degree C increase in ambient temperature, there was a 1 percent increase in the incidence of suicide.
Heat can affect mental health treatments as well. For instance, patients taking lithium are at a higher risk of toxicity, as dehydration raises their blood lithium levels. Many psychiatric medications, such as antipsychotics, antidepressants, and antiepileptics, can make it harder to regulate body temperature, making patients more vulnerable to heat stroke and other heat-related health problems. People with mental disorders are three times more likely than others to die during a heat wave.
How can heat affect our mental health? It is through many different pathways, both direct and indirect. Heat affects our biochemistry and alters the production of serotonin and dopamine. It also raises our core temperature, which affects physiological processes in our brain and body, interfering with cognition. For example, heat can suppress the production of thyroid hormones, causing lethargy, depression, and cognitive impairment. Increased sweating causes dehydration, leading to cognitive dysfunction and general lethargy.
Heat also has many indirect effects. It disrupts sleep (most of us need to be cool to sleep well), making us exhausted and more vulnerable to stress. It worsens heart function, hurting all our other organs, including the brain.
Another indirect effect is the worry we feel about our environment. There may even be a new syndrome developing, variously called eco-anxiety, climate anxiety, climate trauma, eco-grief, or climate grief. These terms refer to the anxiety and grief caused by climate change, including changes in our local environment (water levels, growing seasons) and those we may only hear about, such as lost species (as with dying coral reefs) or the melting of the glaciers. The American Psychological Association and ecoAmerica suggest that people are under increased stress due to feeling hopeless about how little governments are doing to address the potential climate cataclysm.
What can we do? First, we must remember that we must address our health before we can help others. We should stay indoors during heat waves, avoid direct sunlight, and hydrate frequently. We should wear loose-fitting clothing to allow our bodies to release heat more efficiently and avoid strenuous activity, especially during the hottest hours of noon until about 5 pm. Those who must work outdoors need frequent breaks and some cool shelter to use regularly. And the most vulnerable, including those without a home or having no access to air conditioning, should use public spaces like libraries or other suitable public spaces.
The mental health system will be particularly challenged as temperatures rise. This is most true for the already resource-stretched facilities that treat the socioeconomically disadvantaged among us. They will need new approaches and additional resources to cope with what is likely going to be an increased need for mental health care services.
Ultimately, the solutions are social and political. As a society, we have to address the problems of climate change.
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