The Effects of Heat on Older Adults

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The news in summer 2021 was almost as oppressive as the heat itself. Boston sweated through its hottest June on record. Lytton, British Columbia, reached an unheard-of 121 degrees Fahrenheit as the Pacific Northwest baked under a heat dome. Another dome in August stifled the Mediterranean.

As records toppled, lives were lost. Early investigations suggest that nearly one thousand people died as a direct result of the Pacific Northwest heat wave. Most of them were older adults.

In Oregon’s Multnomah County, which includes Portland, the average age among those who perished was 70. People over 65 accounted for three-quarters of Washington’s deaths.

These proportions, which echo the casualties following extreme heat events around the world in recent years, reiterate that older people are among those most vulnerable to falling ill and dying when the mercury rises. More than 80 percent of the estimated 12,000 people in the United States who die of heat-related causes annually are over age 60, according to the journalism resource Climate Central. As Earth gets hotter and human populations skew older, heat-related fatalities among older adults are expected to grow.

Climate change drives more frequent, more intense, and longer heat waves. It raises nighttime lows, preventing body temperatures from resetting when the sun sinks. Even short of heat waves, the volatility that climate change provokes in day-to-day highs can truncate the lives of older people with certain health conditions, researchers at the Harvard T.H. Chan School of Public Health wrote in a 2012 study in PNAS.

Clinicians can help. A survey published in the Annals of Global Health in 2015 indicated that primary care physicians are U.S. adults’ most trusted sources of information related to climate change and health. The medical toolkit grows as research continues to reveal the biological and social factors that make older adults more susceptible to heat and identifies the most effective interventions.

Studies show that it can be hard for even healthy older adults to tell when it’s too hot or if they’re dehydrated. Cognitive decline exacerbates these problems. Older bodies also hold more heat than younger ones when the temperature climbs. Glands don’t release as much sweat. The heart doesn’t circulate blood as well, so less heat is released from vessels in the skin. Systems from the cardiovascular to the immune struggle to compensate.

Older adults are likely to have chronic health conditions and to take medications that contribute to heat intolerance. Clinicians best serve patients when they stay abreast of the literature on risk factors and, when heat looms in the forecast, consider warning, checking in with, or adjusting relevant medications of the vulnerable, says Francesca Dominici, the Clarence James Gamble Professor of Biostatistics, Population, and Data Science at the Harvard Chan School.

“So many heat-related hospitalizations and deaths are preventable,” she says.

While doctors have known about many risk factors for decades, others are emerging. By applying statistical expertise to vast health care and meteorological data sets, Dominici and colleagues have uncovered previously unappreciated conditions that raise older people’s likelihood of being hospitalized during and immediately after heat waves. These findings, first reported in JAMA in 2014, include fluid and electrolyte disorders and urinary tract infections.

Data science is “giving us enormous ability to disentangle the major causes of a hospitalization and say reliably that it was the heat that made someone sick,” Dominici says.

What constitutes excessive heat goes beyond the National Weather Service definition of a heat wave, according to findings from researchers including John Spengler, the Akira Yamaguchi Professor of Environmental Health and Human Habitation at the Harvard Chan School.

“We’re seeing problems with hydration, sleep, and cognitive decline at 85 degrees and lower,” he says. “It makes us rethink what real heat stress is about.”

Dominici and others point out that temperatures don’t have to hit 90 or 100 degrees to be dangerous; they only have to rise beyond a region’s normal range.

Acclimation matters. Heat tends to cause more deaths at the start of summer than at the end. More deaths occur when heat strikes areas unaccustomed to it.

Finally, age intersects with socioeconomic factors to compound heat vulnerability. Older adults who are poor, who identify as Black or Hispanic, or who live in cities are more likely to become sick or die from excessive heat. Poorer neighborhoods tend to have fewer shade trees and reach a boil faster than wealthier environs. Having air conditioning at home isn’t enough if a patient can’t afford to run it. The Arizona county that includes Phoenix reported that of those who died indoors of heat-related causes in 2019 fully 91 percent had air conditioners, but the units were turned off, turned too low, or broken. Older adults with mobility issues or who lack social networks are less able to access resources such as cooling centers or have people check on them.

Science and medicine have made tremendous progress in understanding how our warming climate threatens human bodies, says Dominici. Now it depends on everyone, including clinicians, to act quickly enough to avoid the worst.

Stephanie Dutchen is manager of feature content and multimedia in the HMS Office of Communications and External Relations.

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