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Physicians warned of both the physical and mental health impacts of extreme heat, particularly for vulnerable populations, during an hosted by SciLine last week.

"We know that about 30 deaths per year occur [among] ... children left in cars," said Perry Sheffield, MD, MPH, of the Icahn School of Medicine at Mount Sinai in New York City, cautioning that cars can get "deadly hot" even when the outside temperature is under 70° F.

While these deaths are rare, the much more common heat-related deaths have no red flags, she noted. "So whether or not heat plays a role and how it plays a role is really pretty unquantified."

A many as 11% of emergency department visits to U.S. children's hospitals in the warm seasons were attributable to hot temperatures, according to a study that Sheffield and colleagues published in in January.

Another vulnerable demographic are people with sickle cell disease, who are "exquisitely sensitive" to dehydration, Sheffield said. Under stressed conditions, their red blood cells' walls change shape, which can cause clotting or "micro-clotting" that can affect several organs. Even those with sickle cell trait -- those carrying just one copy of the gene that causes sickle cell disease -- may be more prone to health effects from heat.

"Up to 3 million people living with sickle cell trait are at a higher risk of sudden death during exercise in hot weather," she added.

Researchers are also beginning to ask questions about the longer-term impacts of heat on health; for example, the effect of repeated exposures to heat and dehydration on the kidneys. They are also looking at other genetic variations that may increase "heat health risks," such as muscle contractility.

Extreme Heat and Mental Health

Amruta Nori-Sarma, PhD, of Boston University School of Public Health, said that her research has looked at "the burden of both physical and mental health" associated with extreme heat days, which are anticipated to increase with climate change.

She noted that in the continental U.S. have occurred since 2015. The warmest year on record was 2016, followed by 2019 and 2020.

Direct physical effects from heat exposure include heat stroke, heat stress, swelling, and heat rash, while indirect physical effects are often due to underlying conditions, which can lead to cardiovascular illness and renal insufficiency.

While physical effects are well-researched and documented, the impacts of heat exposure on mental health are "poorly understood," Nori-Sarma said.

She and her colleagues examined the relationship between warm season months (May-September) and mental health-related emergency department visits from 2010 to 2019 in a study that was published in in February.

"What we found in this study is that as temperature increased, the rates of emergency department visits for mental health across all of the mental health causes that we're interested in correspondingly saw an increase," Nori-Sarma noted, which included substance use disorders, anxiety, mood disorders, schizophrenia, and self-harm.

"This indicates to me that heat is likely to be an external stressor that is exacerbating people's existing mental health conditions," she added.

With regard to pathways that could impact individuals' mental health during these periods, "one of the things that we could hypothesize would be disrupted sleep periods that are happening because people are experiencing high temperatures, or even daytime discomfort or irritation," she said. Another pathway that might impact younger people in particular is stress related to climate change.

Prevention

Nori-Sarma pointed out that Boston has proposed and is beginning to implement a climate adaptation plan to reduce people's vulnerability to heat, which includes building green spaces, and leveraging sustainable design to reduce people's exposure to heat and extreme cold inside buildings.

In addition, one of her doctoral students, Ken Adams, is working to produce a report on the locations of cooling centers in 70 different cities.

Nori-Sarma and Sheffield also touched on one other vulnerable demographic -- outdoor workers who have occupational exposures to extreme heat. One of the ways employers can prevent adverse outcomes for their workers is to provide them with shade from the sun and encourage more frequent water breaks and rests.

Another strategy has been to eliminate working hours that fall during the hottest parts of the day, Nori-Sarma said, which would mean starting work earlier in the morning and working a little bit later in the evening.

Sheffield pointed out that the National Institute for Occupational Safety and Health built a mobile app to educate both workers and employers about the risks of extreme heat, which also sends alerts on high-heat days, as well as tips for safety precautions.

Hospitals already leverage electronic medical records to send out alerts to vulnerable patients on incoming hurricanes and high winds as a matter of disaster preparedness, Sheffield noted. Extreme heat might be one more alert they should consider.

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