Around the world, several devastating heatwaves are ongoing with forest fires and extreme temperatures threatening human life and well-being. The detrimental effects of extreme heat on physical health and ecosystems have received significant attention. But heatwaves can also have a profound impact on mental health, and this has not been widely recognised so far. In this blog post, we dive into the science behind heat and mental health. We discuss the underlying mechanisms and the urgent need for proactive measures to protect the psychological well-being of individuals during extreme heat events.
Heatwaves can impact mental as well as physical health
Whilst the connection between heat and mental health might not be immediately apparent, research has begun to uncover the intricate relationship between the two. The foremost impact of heatwaves on health stems from the physiological responses of the human body to extreme heat. When exposed to high temperatures, our bodies strive to regulate internal temperature through perspiration and dilation of blood vessels. One study showed that rats exposure to extreme heat (heat maintained at 43 °C and 60 ± 10 % humidity for 15 min once a day) was enough to lead to changes in the hippocampus, a small structure deep in the brain linked to memory and many other cognitive functions. These changes are easily measurable in animal research. But how does heat alter human mental health?
Burke and colleagues tested the association between extreme heat and suicide in the US and Mexico. The authors showed that monthly temperature was associated with monthly suicide rates in both countries. This was different from the relationship between heat and ‘all-cause mortality’: death from all causes, which typically increases at both extreme hot and cold temperatures. Worryingly, the authors also looked for whether various adaptation measures, such as air conditioning could lessen the health-related impacts of climate over time. However, there was no statistically significant decline in the association between temperature and suicide, suggesting increasing air conditioning was not making a difference.
Finally, the authors investigated whether average monthly temperatures were linked to how much depressive language was posted on social media in the US. They also found an association, with temperature over time correlated with depressive language on social media. When temperatures were hotter people posted more depressive language and they posted less depressive language when temperatures were cooler.
This study is important and seems to support a link between heat and increases in suicide rates, and depressive language. However, why the two are associated is still unclear. It is perhaps unusual that adaptation measures like air conditioning were thought to not have an effect, as if cooling doesn’t change the association why are they linked in the first place? Another study also showed that precipitation had a slightly stronger impact on depressive language posted on Twitter than heat did, again suggesting it might be the extremes of weather rather than heat specifically. Nevertheless, it is clear that no study finds extreme heat is good for mental health.
Heat and sleep
It is well-known that prolonged heat exposure can disrupt sleep patterns, with hot nights leading to restless sleep and exhaustion the following day. Sleep disturbances have long been recognized as a significant risk factor for mental health issues, including depression and anxiety. This vicious cycle of heat-induced sleep disruption could exacerbate existing mental health conditions and possibly trigger new ones. One study used the clever methodology of linking data from sleep-tracking wristbands to sleep records across 68 countries to local meteorological data. They found that increased temperature was associated with people not falling asleep as quickly shortening the duration of sleep overall.
How does heat affect different people’s mental health
While heatwaves can affect anyone, certain populations are particularly vulnerable to the mental health impacts. The elderly, who are more susceptible to heat-related illnesses, often face increased social isolation during extreme temperatures. Low-income communities, living in urban heat islands, are less likely to have access to air conditioning and green spaces, amplifying the psychological burden of heatwaves. Additionally, children and pregnant women are at risk, with heat exposure during pregnancy potentially leading to adverse birth outcomes and developmental issues in children.
Climate change and altruism
Although climate change impacts negatively mental health there is also evidence that extreme circumstances can inspire altruism and cooperation. For example, studies examining the aftereffects of natural disasters suggest that people may behave more altruistically, an effect that was also reported during the Covid-19 pandemic. Intriguingly other studies have suggested that older adults might be more altruistic than younger adults, suggesting effects of an aging population may also present opportunities. However, whether older adults will be more altruistic with issues such as climate change is debated. Future studies can try to understand differences between people in altruism, and how they relate to pro-environmental behaviours, as a positive climate mitigation strategy.
As people around the world continue to grapple with the increasing frequency and severity of heatwaves, it is imperative to recognize and address the profound impact these events have on mental health. Current research points to multiple pathways by which extreme weather could affect mental health. Future research needs to understand more about the mechanisms for why they are linked so that we can intervene successfully. Understanding more about social factors such as altruism and different population demographics will be crucial to reducing its negative impact in a way that is relevant for people around the world.