When people hear a heat annoying in their homes, report an increase in impulsive behavior. In neighborhoods with lower-income families and fewer tree canopies, residents also noted that they were easily angry and verbally aggressive.
Heat seizes aggression
The research, published on the preprint server PsyarXivwas conducted by Kimberly Meidenbauer, assistant professor in the Department of Psychology at Washington State University, with colleagues from the University of Chicago. Her goal: to better understand how heat affects mood and mental health in real-life settings.
The links between heat waves and antisocial behavior have spawned decades of theories. Psychologists and others have probed the correlation between high temperatures and higher rates of domestic violence, assaults, and hospital admissions for drug overdoses and suicide attempts.
Despite the social cost, much remains unknown about the impact of heat on emotional well-being, Meidenbauer says. “There honestly hasn’t been a lot of research on this, and most of the work has been done in labs with people performing cognitive tasks. I wanted to study this problem with a diverse and representative sample of people in a real-world context with lots of detail.”
Meidenbauer and his team conducted surveys from May to September, analyzing census data for insights into household income, neighborhood tree canopies, access to parks, and the urban heat island effect, as well as how much people they self-reported. Respondents were spread across the Chicago metropolitan area.
The number of people experiencing heat stress in their homes and reporting impulsive behaviors was concerning, she says.
“The idea here is that if you are more impulsive, you may be more likely to engage in risky behaviors, including substance abuse and self-harm. Even after the heat dissipates, the impulsivity seems to persist for a while, which is pretty crazy,” says Meidenbauer.
Heat appears to affect the brain’s prefrontal cortex, which is important for planning, self-control, and emotional function.
“Some studies show that, with heat exposure, the connectivity of the prefrontal cortex with other important brain regions is disrupted,” Meidenbauer says. “Other studies suggest that when the body is thermoregulating, it drains resources, which could be cognitively taxing.”
Heat also affects many of the psychotropic medications used to treat mental illnesses, which could be a factor in self-harm, he says. Additionally, some types of aggression have been linked to impulsive behavior.
Meidenbauer says the study’s findings underscore the need for resources to protect people’s mental health during heat waves.
“Going forward, we need to focus on infrastructure that can cool things down,” he says. “This includes buildings designed with passive cooling systems and urban green spaces that reduce the heat island effect.”
But in the short term, access to affordable cooling systems will be critical for low-income and at-risk populations, Meidenbauer says.
“The biggest mitigating factor for heat,” he says, “was whether respondents had access to air conditioning in their homes and whether they could afford to run it.”
During a heat wave, even high indoor temperatures can prove dangerous
During hot weather, most of the public’s attention is focused on the skyrocketing outdoor temperatures that can cause serious medical complications such as heat stroke.
For many people, especially those without access to air conditioning, indoor temperatures can also become dangerous, said Leah Schinasi, associate professor of environmental and occupational health at Drexel University.
In a recently published paper reviewing research on indoor overheating, Schinasi and other Drexel researchers noted that many vulnerable people, including the elderly and the very young, spend most of their time indoors, but may not be able to adequately cool their homes during a heat wave.
“It can actually be hotter inside than outside, and that’s a really important environmental justice issue,” Schinasi said. “Many people with low incomes do not have access to air conditioning, and if they do, many are unable to afford the energy costs associated with their use.”
This can lead to dangerously high temperatures indoors, which can have a significant impact on a person’s health, the study authors wrote. Overheating indoors can lead to heart and respiratory problems, a higher risk of blood clots, and impaired kidney function, among other problems.
In the United States, extreme heat causes more deaths on average than any other extreme weather event, researchers noted, highlighting a report from the Centers for Disease Control and Prevention.
“It is important to underline that heat is a danger to people’s health. It has not historically been recognized as an environmental hazard,” Schinasi said.
The dangers of high indoor temperatures have been little studied, he added, saying it is critical that public health officials consider the needs of people who cannot shelter in an air-conditioned home during a heat wave.
During heat waves, people can close blinds to block some of the radiant heat, stay hydrated, wear light clothing and take showers to cool off. Some people will need to find attractive places outside their homes, like the cooling centers that Philadelphia health officials open during heat emergencies.
People should also consider checking on neighbors who live alone and who may not have adequate air conditioning. (The study found that older people sometimes have difficulty sensing how hot it is and may not realize they are at risk for adverse health effects.)
Cities should take long-term measures to counter the “heat island” effect, which makes it particularly difficult for urban residents to withstand a heat wave.
Philadelphia neighborhoods without much shade from trees and older homes can be difficult to keep cool. Schinasi said, “Think about those brick row houses, the old building stock that is extremely close to each other, like an oven: they can get very, very hot. And the flat, dark roofs we see in certain parts of Philadelphia absorb rather than reflect radiant heat and can contribute to extremely high temperatures indoors.”
Planting trees or building shade structures can lower sidewalk temperatures. Dark pavements can be painted lighter colors so they reflect, rather than absorb, heat.
And, he said, officials should consider offering air conditioning to people who don’t have one, as well as subsidizing summer cooling costs. Pennsylvania has a program that helps eligible residents get free air conditioners; a similar program in New Jersey helps residents cover their energy bills.
“We need to think about how to make residential environments safer,” Schinasi said. “People who lack resources and social support will be the ones who bear the brunt of a heat wave.”
Excessive heat and its impact on mental health
This summer’s extreme heat is affecting people across the country, both mentally and physically. While heat can make anyone irritable, the impact can go beyond that, especially for people with mental health issues. A Baylor College of Medicine psychiatrist explains how heat affects mental health
Excessive heat causes changes in emotions and behavior that can result in feelings of anger, irritability, aggression, discomfort, stress, and fatigue. Heat alters these behaviors because of its impact on serotonin, the main neurotransmitter that regulates mood, leading to reduced levels of happiness or joy and increased levels of stress and fatigue.
The most vulnerable groups affected by heat and mental health include people with pre-existing conditions and people who use substances such as alcohol. People who already suffer from stress, anger or anxiety will experience an increase in serotonin. If people use substances, especially alcohol, they need to be more hydrated. Combining substance use with heat requires even more hydration.
“All mental illnesses get worse in the heat because it causes more tiredness, irritability and anxiety and can exacerbate depressive episodes,” said Dr. Asim Shah, professor and executive vice chair of the Menninger Department of Psychiatry and Behavioral Sciences at Baylor.
Signs of heat compromising mental health begin with irritability, decreased motivation, aggressive behavior, and sometimes brain fog. In the worst cases, it can cause confusion and disorientation. While avoiding the heat may not be possible, Shah recommends hydrating with electrolytes and keeping your head covered when going outside.
Also, pour some water on your head to cool down and try to do things in the shade. If you usually go for walks outside, move them inside by walking in the mall or in a large air-conditioned space.
If you are taking medications, check with your doctor before mixing your dose with excessive heat. Some mental health medications, such as lithium for bipolar patients, may not mix well with heat. Lithium passes through the kidneys, so if you sweat more, your lithium levels will fluctuate.
“If you are out in the heat and using lithium, the levels may fluctuate. In such a scenario, we have to be very careful and adjust the dosage of lithium or avoid heat,” she said.
Climate change, including droughts and extreme temperature changes, can cause adverse effects by increasing pollutants and allergens and worsening air quality. These worsen mental health problems such as depression, anxiety or PTSD. Some studies show that exposure to any natural climate disaster can increase the risk of depression by more than 30%, anxiety by 70%, and both by more than 87%.
“Children are a vulnerable population because of their physical and cognitive immaturity. They are exposed to more pollutants and allergens because they spend more time outdoors,” Shah said.
Previous studies of emergency room visits explore hospital visits due to heat and mental health. A study in JAMA Psychiatry reported an approximately 8% increase in emergency room visits due to the effects of heat on mental health. If you feel affected by intense heat, talk to your primary care doctor or mental health professional.
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