Researchers have examined how hot may be too hot for the human body to function optimally – as forecasters predict 30C temperatures from today and into the weekend.
Researchers at the University of Roehampton say an upper critical temperature (UCT) exists for humans – and that it is likely to be between 40 and 50C.
Four men and three women participated in the team’s experiment in 2021.
Participants’ respiration rate – to measure their metabolic rate – and heart rate were calculated over 60 minute periods at high temperature exposures, including at 40C.
Ongoing research presented at the annual Society for Experimental Biology conference in Scotland on Thursday suggested temperatures in that range raise a person’s resting metabolic rate – the amount of energy needed to function at rest.
When that happens, we may start to breathe more heavily and our heart rates can go up.
Once a person’s body can no longer get rid of excess heat – a condition known as “heat stress” – the core temperature rises, which can result in confusion, nausea, dizziness, headache or fainting.
Lewis Halsey, a professor of life and health sciences at the University of Roehampton, said the findings are “ever more valuable” in a “warming world”.
He said: “This research provides fundamental knowledge about how we react to suboptimal environments, and how ‘optimal’ differs between people with different characteristics.”
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Pic: University of Roehampton
“We are steadily building a picture about how the body responds to heat stress, how adaptable it can be, the limits to those adaptations, and – crucially – how varied responses are between individuals. In a warming world, this knowledge becomes ever more valuable.”
The team, which is currently collecting more data in a follow-up study, found that our resting metabolic rate can be higher when people are exposed to hot and humid conditions.
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The results indicated that people’s resting metabolic rates rose when they encountered temperatures of at least 40C.
The results indicated that at 40C there was a 35% change in the metabolic rate in comparison to rest in the thermoneutral zone – the temperature in which the body does not have to work to generate or lose heat – which is between 28 and 32C.
The research comes as thunderstorms are set to strike parts of England over the weekend following high temperatures which prompted a yellow heat-health alert.
The UK Health Security Agency (UKHSA) and the weather agency issued the heat warning until Sunday morning for London, the South East, East Midlands, West Midlands, East of England, and Yorkshire and the Humber.
https://news.sky.com/story/how-hot-is-too-hot-for-the-human-body-to-function-study-reveals-how-we-respond-to-heat-stress-12916641
