MONDAY, Dec. 9, 2024 (HealthDay News) -- Heat waves caused by climate change have been thought to pose the greatest risk to the world’s elderly, but a new study from Mexico suggests that’s not the case at all.

Instead, three-quarters (75%) of heat-related deaths are occurring there among people younger than 35, researchers reported Dec. 6 in the journal Science Advances.

What’s more, nearly a third of heat-related deaths occurred in young adults ages 18 to 35, the group expected to be most resilient in the face of rising global temperatures.

“It’s a surprise. These are physiologically the most robust people in the population,” said researcher Jeffrey Shrader, of the Center for Environmental Economics and Policy, an affiliate of Columbia University’s Climate School. “I would love to know why this is so.”

For the study, researchers focused on heat-related deaths in Mexico, because that country collects very detailed data on causes of death and daily temperatures.

Between 1998 and 2019, Mexico suffered about 3,300 heat-related deaths per year, the study found.

Results show that, surprisingly, people ages 50 to 70 were least likely to die from excess heat.

Instead, children younger than 5 and young adults 18 to 35 were most likely to be stricken as temperatures rose to dangerous levels, researchers found.

“We project, as the climate warms, heat-related deaths are going to go up, and the young will suffer the most,” said co-lead researcher Daniel Bressler, a doctoral candidate in Columbia’s Sustainable Development program.

Several factors could be causing this increased risk among young adults, researchers speculated.

Young adults are more likely to work outdoor jobs in businesses like farming or construction, and thus are more exposed to dehydration and heat stroke, researchers said.

They also are more likely to work indoor manufacturing jobs in facilities that lack air conditioning.

“These are the more junior people, low on the totem pole, who probably do the lion’s share of hard work, with inflexible work arrangements,” Shrader said in a Columbia news release.

Young adults are also more likely to participate in strenuous outdoor sports, again placing them at risk of heat stroke, the researchers noted.

The risk among infants and small children is less surprising, researchers said.

Their small bodies absorb heat quickly and their ability to cool off quickly by sweating is not fully developed, researchers said. Their immune systems also are still developing, making them vulnerable to infectious diseases that are more common in hot weather.

Temperatures didn’t need to be smoking hot to cause death, either.

Researchers found the largest number of deaths occurred at temperatures of 73 to 75 degrees Fahrenheit with high humidity, likely because that level of heat occurs more frequently and thus more people are exposed regularly to that heat.

The study’s results are particularly troubling for poorer countries in Africa and Asia, researchers said

Only about 15% of Mexicans work in agriculture, researchers noted. Countries in other parts of the world have much younger populations that work more often in manual labor, and thus are much more at risk for massive increases in heat-related deaths.

More information

The U.S. Environmental Protection Agency has more on heat-related deaths due to climate change.

SOURCE: Columbia Climate School, news release. Dec. 6, 2024