Science stunner: People under 35, not seniors, most likely to die from heat

NEW YORK — What if everything we thought we knew about who’s most at risk during extreme heat was wrong? A shocking new study turns conventional wisdom on its head, revealing that in Mexico, it’s actually young people – not the elderly – who are dying more frequently from heat exposure. The research shows that 75% of heat-related deaths occur among people under 35 years old, with many victims being otherwise healthy young adults.

“It’s a surprise. These are physiologically the most robust people in the population,” says study coauthor Jeffrey Shrader of Columbia University’s Climate School in a statement. “I would love to know why this is so.”

The Temperature Paradox

For decades, scientists and public health officials have focused their heat-protection efforts on elderly populations, believing them to be most vulnerable to temperature extremes. But when researchers analyzed death records in Mexico, they discovered something unexpected: between 1998 and 2019, the country experienced about 3,300 heat-related deaths each year, with nearly a third occurring in people ages 18 to 35. Even more surprising, people aged 50 to 70 – who were thought to be highly vulnerable – actually had the lowest rates of heat-related deaths.

To understand this pattern, researchers chose to study Mexico for a specific reason: the country keeps detailed records of both deaths and daily temperatures for every local area, creating a rich dataset for analysis. Think of it as a massive weather-and-health diary covering an entire nation, with entries spanning more than two decades and including information about 13.4 million deaths.

Heat and Humidity: A Deadly Combination

The researchers focused on something called “wet-bulb temperature” – a measurement that combines heat and humidity to show how well our bodies can cool themselves through sweating. While this might sound technical, think of it this way: on a dry, hot day, your sweat evaporates quickly and helps cool you down. But on a humid day, even if it’s not as hot, the air is already so full of moisture that your sweat can’t evaporate as effectively, making it harder for your body to cool itself.

It’s like trying to dry clothes outside. On a hot, dry day, your clothes dry quickly because the air can absorb the moisture. But on a humid day, they stay damp much longer because the air is already saturated with water vapor. Our bodies face the same challenge when trying to cool down in humid conditions.

When wet-bulb temperatures reach around 35°C (95°F), it becomes physically impossible for humans to survive without artificial cooling, because our natural cooling system (sweating) simply can’t work anymore. Even at lower temperatures of 31°C (88°F), our bodies start to struggle significantly with cooling down.

Who’s at Risk and Why

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

The high death rate among young adults, particularly those between 18 and 34, stems largely from their work conditions. “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,” explained Shrader. Young adults typically fill jobs in construction, farming, and factory work – occupations that often involve intense physical activity in hot environments with little flexibility to take breaks or avoid the hottest parts of the day.

Children under 5, especially infants, face different challenges. Their bodies are particularly vulnerable because of their physical makeup: they have a higher ratio of surface area to body weight, which means they absorb heat more quickly than adults do. Their ability to sweat – the body’s main cooling mechanism – isn’t fully developed yet. Adding to their risk, their immune systems are still maturing, making them more susceptible to diseases that become more common in hot, humid conditions, such as those spread by mosquitoes or contaminated water.

Finding the Breaking Point

The researchers discovered that different temperatures affect people differently. They found that young people fare best at wet-bulb temperatures around 13°C (think of a mild spring day with 40% humidity – it would feel like 71°F). However, the highest number of deaths occurred at wet-bulb temperatures of 23 or 24°C – not because these temperatures are the most dangerous, but because they happen more frequently. It’s like how most car accidents happen on familiar roads near home, not because they’re the most dangerous roads, but because we drive on them more often.

While this study focused on Mexico, its implications stretch far beyond its borders. Mexico, where about 15% of workers are employed in agriculture, represents a middle ground in terms of its workforce and age distribution. But consider countries in Africa and Asia, where much larger portions of the population are young and working outdoors in manual labor. If the patterns found in Mexico hold true elsewhere, these nations could face even more devastating impacts as global temperatures rise.

This possibility is particularly troubling because many of these countries also have limited access to air conditioning and other cooling technologies that could help protect workers. A recent study found that farmworkers in many developing nations are already struggling to work in increasingly oppressive heat and humidity.

The Cold Truth

Interestingly, despite all our fears about rising temperatures, cold weather currently claims more lives globally than heat, even in Mexico. The study found that older adults are particularly vulnerable to cold temperatures, partly because their bodies tend to run at lower core temperatures, making them more sensitive to chills. When it’s cold, older people often stay indoors, where infectious diseases can spread more easily.

However, this pattern is changing. Since 2000, the proportion of heat-related deaths has been steadily climbing, and scientists expect this trend to continue as our planet warms. The research team is now expanding their investigation to other countries, including the United States and Brazil, to see if young people face similar risks elsewhere.

The findings from this research, published in Science Advances, challenge us to rethink who needs protection from extreme heat and how we provide it. As our world continues to warm, we need solutions that consider everyone’s vulnerability – from infants to the elderly, from office workers to those laboring outdoors. The answer might lie in better workplace protections, improved access to cooling technology, and stronger climate policies. After all, when it comes to heat-related deaths, age isn’t just a number – it’s a crucial factor in determining who’s most at risk.