Heat and Health
Excessive heat kills people (and pets and other living things)
We are experiencing unprecedented heat waves, breaking record after record.
The 2003 heat wave in Europe killed an estimated 72,000 people, in large part because Europe was little prepared. Such heat waves just weren’t an issue in Europe before, and so there wasn’t a sufficient plan for what to do, or understanding how insidious the effects may be, and there was relatively little air conditioning.
Even after these lessons, it is currently estimated (in September 2022) that 23,000 people died in the mid-summer 2022 heat wave in Europe. The 2022 European heat wave set records; in the UK the temperature broke records that have been kept for hundreds of years. Airports were closed because the runways buckled.
It is estimated that there were almost 62,000 deaths in Europe Between May 30 and September 4 2022, predominantly the elderly and in women more than men. (Ballester J et al. Heat-related mortality in Europe during the summer of 2022. Nature Medicine Vol 29:1857-1866, July 2023).
The United States in mid-July 2022 had over 100 million people under excessive warning or heat advisories.
The summer of 2022 saw the worst heat wave in China’s history.
The heat wave in the western United Sates in early September 2022 had the hottest temperature for a September day ever recorded on Earth: 127 degrees in Death Valley, California.
Nine of the 10 hottest years on record happened in the last 10 years, and 2022 is not likely to disappoint! The heat was modified slightly by a La Nina weather event in 2021, but it was still one of the hottest years on record (NOAA has it as #6)! 2022 was the 5th hottest recorded. The hottest was 2016.
2023 was the hottest year on record and 2024 is on track to beat it.
This is our present, and it will be worse in the future. These high temperatures are extreme weather events themselves and the driver of other extreme weather events that are more common in this age of climate change.
Keep in mind that heat events that can cause severe problems are not limited to periods of heat advisories!
Medical Aspects
Heat-related problems can include cramps, rashes, fatigue, edema (swelling), or more dangerous entities like heat stroke.
Image from https://www.weather.gov/safety/heat-illness That page is a good summary and resource to share.
Peripheral vasodilation as a mechanism to defend against excessive heat (protect the brain by shunting hot blood to the periphery, where it can cool) can cause cardiovascular stress. With dehydration from sweating, this can lead to heat syncope (passing out), and worse, in a vicious negative feedback loop.
“It’s not just the heat, it’s the humidity” is true. If the humidity is high, sweat can’t evaporate so it can’t cool the body. This combined effect of heat and humidity is quantified as the Heat Index.
At a body temperature of 100-102 degrees F (38-39 C) there is a risk of heat collapse. At 105 F (41C) heat stroke and death are possible.
Also keep in mind that medications might be affected by heat or light, a particular concern in there are power outages due to increased electricity use for air conditioning during heatwaves.
Heat sends people to emergency rooms
Emergency room visits and hospitalizations increase during periods of increased heat. These visits can be for the heat problems above, or secondary effects like dehydration, kidney stones, acute or chronic renal failure, and cardiovascular and respiratory diseases.
A study of the records of almost 22 million emergency department visits by adults over 18 from around the United States found that on days of what they considered extreme heat there was an excess of emergency department visits for any cause, heat-related illness, renal disease, and mental illness. These findings were more pronounced in men and in the northeastern United States, but were not limited to the elderly.
There is evidence that direct effects of heat, as well as the compounding problems from some medications used in mental health care (do not stop medications without speaking to your doctor first!), create problems in cognition and emotional resilience.
Here is the data (source: Financial Times) on deaths attributed to heat in Arizona over the last 50 years. Very reminiscent of the Keeling curve of CO2 in the atmosphere, a geometric progression:
One thing to keep in mind, while in heat waves there can be tens of thousands of deaths, that is just the tip of the iceberg of suffering. For example, in 2020 there were 702 deaths in the United States per the CDC, but 67,523 emergency room (ER) visits. What vast resources were used, how many hospitalized, how many would have died, how crowded were the emergency rooms, clinics and hospitals, how much stress on the healthcare system and clinicians? How many individuals weren’t seen, but should have been, with delayed adverse health outcomes that are hard to capture?
Vulnerable people
The elderly, those living in cities, particularly in areas where people can’t afford air conditioning (or the electric bill when they have air conditioners), and urban heat islands (where heat is reflected off concrete and glass, and there is little tree cover) are at high risk.
Vulnerable groups also include infants and children, pregnant women, certain groups (occupational exposures, and in studies in California and elsewhere, African Americans and Native Americans have historically been hard hit in the United States), and those with diseases that may be impacted by heat.
Take care (of yourself and others)
Take precautions. Stay hydrated and out of the sun. As clinicians know well, health professionals play a vital role in advising their patients to stay out of the sun, take shelter, wear hats and use sunblock, know their personal limit for activity in hot weather, drink fluids before you are thirsty (If you aren’t urinating as much as usual, you may be dangerously dehydrated), dress appropriately for the heat, and care for their pets.
Problems can be compounded by poor air quality, and some drugs and medications that alter vascular tone or sweating, or diuretics that can exacerbate dehydration (again, do not stop medications without asking your doctor), as well as drinking alcohol.
While it is important to advise those at particular risk (or those responsible for persons at high risk), anyone can overdo it, including experienced athletes, if they underestimate the heat or overestimate their resilience to heat!
We can remember to check on neighbors and friends or relatives who may be at particular risk.
Additional Resources
There are a lot of patient materials clinicians can use, so many that I suggest you see what your medical society has or do a brief search and see what you are comfortable with. Here is material from the CDC: https://www.cdc.gov/disasters/extremeheat/warning.html
Global Climate Change and Human Health. Lemery, Knowlton, Sorensen eds. John Wiley and sons, 2021. Chapter 3 is about heat and health.
The Lancet Countdown has global statistics and other information about the effects of climate change on health. Very dense and very important.
Video presentations are available from the Dartmouth 2022 course on climate change and health
Here is material available in the resource section of the website of The Global Consortium on Climate and Health out of Columbia University Mailman School of Public Health, including slides, presentations, courses and a bibliography:
https://www.ready.gov has user-friendly material about dealing with extreme weather events due to climate change, including extreme heat.
Sorensen C, Hess J. Treatment andPrevention of Heat-Related Illness. NEJM September 28, 2022 DOI: 10.1056/NEJMcp2210623
Information about heat for clinicians from the government of Victoria in Australia includes wonderful PDF files you can download, including a factsheet for clinicians, toward the bottom of the webpage.
The World Health Organization has suggestions for dealing with extreme heat, as does Yale Medicine. The National Weather Service has a one page PDF handout about heat.
UCLA has developed a heat map that has information about emergency room visits for heat-related problems around California. This is an effort to help plan mitigation efforts and build resiliency. This may be something that would be useful and can be done in other communites.
Of course, there are emergency medical texts, guidelines and articles that cover the medical aspects in greater detail for clinicians.