New research contradicts the widely-held belief that elderly populations are most vulnerable to health issues relating to extreme heat, arguing that young adults are at higher risk.
The paper, published this month in the journal Science Advances, analyzes data from 1998 to 2019 in Mexico, concluding that 75 per cent of heat-related deaths occur in individuals under the age of 35, with the most vulnerable group falling into the 18-35 demographic.
“It’s a surprise. These are physiologically the most robust people in the population,” said Jeffrey Shrader, coauthor and researcher at Columbia University’s Center for Environmental Economics and Policy, said in a statement, given this age group has long been thought to be among the most resistant to heat stress.
Researchers identified 3,300 heat-related deaths per year during the study period.
While young adults accounted for roughly a third of deaths, children under five, especially infants, were also identified as a vulnerable group — although this finding is already established.
The paper found people in the 50 to 70 age range experienced the fewest incidents of heat-related mortality.
The publication follows an unusually warm spring: Between April 13 and early June, Mexico saw three persistent heatwaves, breaking temperature records in more than a dozen cities, including Mexico City. In some places, temperatures climbed as high as 45°C.
Outdoor activity, manual labour likely culprits
The authors posit that several factors contribute to the vulnerability found in young adults.
For starters, many work in outdoor manual labour jobs like farming and construction, elevating the risk of intense heat exposure and dehydration. Indoor manufacturing in poorly ventilated spaces without air conditioning could also be a factor.
“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.
Outside work, young adults are more likely to engage in strenuous outdoor sports than older adults, further increasing exposure.
Physiological challenges for children
The link between heat-related death and children is already established, the authors say. Children absorb heat quickly and their ability to cool off via sweat is not yet fully developed. Immature immune systems also make them more vulnerable to diseases that thrive in humidity.
Temperature risk thresholds
Researchers looked at temperatures on the wet-bulb scale, which quantifies the combined effects of heat and humidity.
Wet bulb scale
They found wet-bulb temperatures of 23–24°C were linked to the highest mortality rates, largely because these temperatures are most common.
Cold weather a risk for the elderly
It appears elderly adults are at a higher risk of health complications relating to the cold, the study found, possibly due to lower core body temperatures.
Staying indoors to avoid cold weather may not help, as it can increase disease transmission.
Heat-related deaths on the rise
Heat-related deaths have been increasing steadily for more than 20 years, and the trend is expected to continue.
In Canada, several heat records were broken this summer. A 2024 study warm weather contributes to 470 deaths, 225 hospitalizations, 36,000 emergency room visits, 7,200 ambulance rides, and 15,000 calls to Info-Santé annually in Quebec alone.