Key points

  • The National Weather Service has issued extreme heat warnings or heat advisories across large swaths of the Midwest and the Eastern U.S. as the July Fourth holiday weekend begins.
  • Hundreds of people die of heat-related illness in the U.S. each year, and heatstroke can cause multiple organ failure, kidney failure, or trigger a heart attack, according to physicians.
  • Certain medications — including blood pressure drugs, antidepressants, and ADHD stimulants — can increase vulnerability to heat-related illness, physicians told NPR.
  • The National Weather Service’s HeatRisk tool accounts for local temperature anomalies, heat duration, and humidity, and is more accurate than heat-index values alone, officials said.
  • Higher temperatures are linked to increased emergency department visits for mental health conditions and higher suicide risk, researchers said.

Extreme heat warnings cover Midwest, Eastern U.S. as holiday weekend begins

Large swaths of the Midwest and the Eastern U.S. are under extreme heat warnings or heat advisories as the July Fourth holiday weekend begins, according to the National Weather Service. Hundreds of people die of heat-related illness in the U.S. each year, and heatstroke can damage the body, leading to multiple organ failure or kidney failure, and can trigger a heart attack, physicians said.

There is no absolute temperature at which heat turns dangerous, Lewis Halsey, a professor of environmental physiology at the University of Roehampton in the U.K., told NPR. Risk depends on individual circumstances, how acclimated a person is to heat, and duration of exposure, he said. Humidity is a key factor — sweating cools the body more effectively in dry heat than in humid conditions, Halsey said.

“If it’s a very humid day and there’s no wind speed, then you are more at risk, even if the air temperature is lower,” Ashley Ward, director of Duke University’s Heat Policy Innovation Hub, told NPR.

The National Weather Service issues heat advisories and warnings based on the local heat index, which accounts for both air temperature and humidity. But Nick Staub, incident commander for extreme heat response in Maricopa County, Ariz., said the agency sees “a significant number of heat-related deaths on days that are not an extreme heat warning.” Heat index values are calibrated for shady locations with light wind; in direct sunlight, temperatures can feel 15 degrees hotter, Staub said.

The NWS’s HeatRisk tool accounts for how far above normal the current temperature is for a given location and time of year, heat duration, and humidity forecasts, offering a more comprehensive risk assessment than heat-index values alone.

Certain groups face elevated risk, including infants and small children, people in their 60s and older, pregnant women, outdoor workers, and those without access to air conditioning, according to NPR reporting. People with chronic health conditions or on certain medications are also at higher risk.

Blood pressure drugs, which millions of people take, are diuretic and can cause dangerous dehydration when combined with heat, Wafi Momin, a cardiologist at Memorial Hermann Health System in Katy, Texas, told NPR. Anticholinergic medications, including Benadryl, and stimulants such as ADHD drugs can impair the body’s ability to cool off, physicians told NPR. ACE inhibitors can make it harder to notice thirst, and beta blockers can decrease sweating, according to medical experts.

“When you’re taking these medications and you’re exposed to heat, it’s like asking a car to drive up a mountain in the summer with the air conditioner broken,” David Eisenman, a physician and researcher at the University of California, Los Angeles, told NPR.

Psychiatric medications including antipsychotics and some antidepressants can reduce sweating, and sedative medications like benzodiazepines may reduce alertness and perception of heat, Dr. Ashwini Nadkarni, a psychiatrist at Mass General Brigham in Boston, told NPR. Patients should continue taking prescribed medications but should take heat risks seriously and make a plan to stay cool, Eisenman stressed.

The warning signs of heat exhaustion include fatigue, extreme thirst, nausea, headache, shortness of breath, rapid breathing, muscle cramping, and dizziness, according to Dr. Matt Leonard, an attending emergency physician at Suburban Hospital, Johns Hopkins School of Medicine. Heatstroke — a more serious emergency — can include a strong, rapid heartbeat, confusion, vomiting, seizures, slurred speech, or passing out, with a body temperature exceeding 103 degrees Fahrenheit, Leonard said.

The first step for anyone exhibiting symptoms is to stop activity and rest out of the sun, Leonard said. Cooling measures include getting into air conditioning or shade with a fan or breeze, misting with a spray bottle, or pouring water over the head. The most important areas to cool are the head and face, armpits, and groin, he said. If symptoms point to heatstroke — especially neurological symptoms like confusion — the person should be taken to an emergency room immediately.

Higher temperatures are linked to higher rates of emergency department visits for mental health conditions and addiction, researchers said. A recent study found that suicide risk also increases with temperature. “We think that every summer roughly an additional hundred young adults are dying by suicide due to increasing temperatures,” study author and psychiatrist Dr. Joshua Wortzel at the Hartford HealthCare Institute of Living, who runs the institute’s Heat Mind Lab, told NPR.

If you or someone you know may be struggling with suicidal thoughts, contact the 988 National & Suicide Crisis Lifeline by calling or texting 988.