We May Be More Vulnerable to High Temps Than Previously Thought, as Heat Waves Kill Thousands Around the World

Intense heat waves are causing humanitarian disasters around the world, with India, Mexico, the Middle East and the United States baking under extreme temperatures, with records being broken in all affected regions. In Saudi Arabia, nearly 1,200 Muslim pilgrims participating in the annual Hajj to Mecca have died between June 14 and 19, the result of a heat wave that drove temperatures above 50°C (122°F). Authorities in the stricken regions are urging their populations to find a way to keep cool, at a time when human-caused climate change is increasing the chances that life-threatening heat events will occur.

Key to countering the adverse health effects brought about by high heat levels is research into how these conditions affect the human body, including efforts being made by researchers at Australia’s University of Sydney and Pennsylvania State University. Testing healthy volunteers under hot-box conditions, the researchers found that the human body may be more vulnerable to high heat levels than previously assumed.

While heat itself can be dangerous, high humidity can exacerbate its effects, turning otherwise tolerable dry heat conditions into a deadly situation. Measured with a combination of local temperature, humidity and wind conditions, it has been long assumed that a wet-bulb temperature of 35°C (95°F) was the point where health problems begin to occur, but the team led by Pennsylvania State University physiology professor W. Larry Kenney found that this point appears to occur further down the thermometer, at 30.5°C (87°F).

However, this key temperature was found to only apply to the study’s young, healthy volunteers: for older participants, the wet bulb temperature threshold was only 28°C (82°F); while dry conditions allowed both the young and elderly to continue to function normally up to 52°C (125.6°F) and 43°C (109.4°F), respectively, moderate to high humidity quickly eroded both groups’ resilience.

“Humid heat waves kill a lot more people than dry heat waves,” Kenney warned.

Heat typically kills in three ways, with the first commonly known as heatstroke: when the body’s internal temperature rises, the body redirects blood flow to the skin in an attempt to shed the excess heat; however, this process diverts oxygenated blood away from the stomach and intestines, allowing toxins that would ordinarily be contained by the digestive system to leak into the circulatory system.

“That sets off a cascade of effects,” according to professor of heat and health Ollie Jay, who runs the thermoergonomics laboratory at the University of Sydney. “Clotting around the body and multiple organ failure and, ultimately, death.”

This diverting of the body’s blood flow also causes blood pressure to drop, leading to the second way that an individual can succumb to heat: the heart has to work harder to compensate for the lack of blood flow to the affected areas, leading to extra strain being put on the heart; this can lead to cardiac failure, especially in individuals with cardiovascular disease.

“You’re asking the heart to do a lot more work than it usually has to do,” Jay said. For someone with a heart condition “it’s like running for a bus with [a] dodgy (hamstring). Something’s going to give.”

The third danger, dehydration, is more straightforward: the overheated individual loses water through sweat, at first placing stress on the kidneys, followed by a drop in blood pressure—exacerbating the circulatory conditions seen in the first two hazards—causing the internal organs to shut down from lack of oxygen and other nutrients, “leading to seizures and death,” according to Harvard University professor of public health Dr. Renee Salas.

“Dehydration can be very dangerous and even deadly for everyone if it gets bad enough—but it is especially dangerous for those with medical conditions and on certain medications,” Salas, who is also an emergency room physician at Massachusetts General Hospital, warned.

With no apparent outward symptoms, heatstroke can overtake an individual, who might otherwise be unaware of what is happening; by the time the individual realizes that they’re in trouble, they typically need urgent medical attention. “We call it the silent killer because it’s not this kind of visually dramatic event,” Jay explained. “It’s insidious. It’s hidden.”

Along with a core temperature that exceeds 40°C (104°F; the body’s normal resting temperature is 37°C/98.6°F), the typical symptoms of heatstroke include confusion in the affected individual, caused by the brain becoming overheated.

“One of the first symptoms you’re getting into trouble with the heat is if you get confused,” explained University of Washington public health and climate professor Kris Ebi. Unfortunately, the confusion itself can prevent the individual from realizing what’s happening.

Authorities are reminding people without access to air conditioning to take basic steps to avoid heatstroke, such as maintaining proper hydration; take cold showers or baths; keep in the shade as much as possible, and close blinds and curtains to prevent sunlight from warming your house; make use of fans to maintain air circulation; and use cold compresses or wet cloths on your neck or wrists as an additional method of keeping cool, especially as these high temperatures are forecast to continue into July.