Extreme heat poses a greater risk to younger populations than the elderly, according to a new analysis which revealed that 75 per cent of heat-related deaths in Mexico from 1998-2019 occurred among those aged under 35 years.

Researchers, including those from Columbia University, US, said the findings challenge the conventional belief that the elderly population are especially vulnerable to extreme heat on its head.

"It's a surprise. The young are physiologically the most robust people in the population. I would love to know why this is so," co-author Jeffrey Shrader of the Center for Environmental Economics and Policy, Columbia University's Climate School, said.

Published in the journal Science Advances, the team analysed excess deaths -- the number of deaths more or less than the average -- with 'wet-bulb' temperatures, a metric that combines heat and humidity or humid-heat to measure their intensified effects.

They found that over the two decades, the country suffered about 3,300 deaths a year related to heat, with nearly a third occurring in people aged 18-35 years. Children aged under five years, especially infants, too were found to be highly vulnerable.

However, people aged 50 years and above, usually considered at high risk in a warmer future, suffered the least levels of heat-related death. Instead, people in the age group died predominantly from modest cold, the team found.

They explained that while Mexico is mainly tropical and subtropical, there are many climate zones, including high-elevation areas, that can get relatively chilly.

The authors said, younger people are predominantly vulnerable to heat, with 35 years old accounting for 75 per cent of recent heat-related deaths and 87 per cent of heat-related lost life years.

Those 50 and older account for 96 per cent of cold-related deaths and 80 per cent of cold-related lost life years, the authors wrote.

According to researchers several factors are at work, for instance young adults are more likely to be engaged in outdoor labour, such as farming and construction activities, and thus could be more exposed to dehydration and heat stroke.

The same could go for indoor manufacturing in spaces lacking air conditioning, they said.

"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.

Young adults are also more likely to participate in strenuous outdoor sports, the researchers said.

They cited a previous study by Mexican researchers which has shown that death certificates of working-age men were more likely to list extreme weather as a cause than those of other groups.

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

Mexico was chosen for the analysis as the country collects highly granular geographical data on both mortality and daily temperatures, the team said.

They added that despite attention given to global warming and its dangers, extensive research has revealed that cold, not heat, is currently the world's number one cause of temperature-related mortality, including in Mexico.

However, heat-related deaths have been climbing in proportion since at least 2000, a trend that is expected to continue, the authors said.

Except for the headline, this story has not been edited by The Telegraph Online staff and has been published from a syndicated feed.