As climate change continues to push global temperatures to unprecedented levels, a new study by researchers from the University of Roehampton in England has brought to light how extreme heat affects the human body. This research comes at a time when July 4 was marked as the hottest day ever recorded on Earth, as reported by Medical News Today. Scientists have now offered a clearer understanding of what happens inside the body when the environment becomes dangerously hot.
The study was presented at the annual meeting of the Society for Experimental Biology held in Edinburgh, Scotland. It examined how the human body responds to rising heat and humidity, focusing on the point at which the body can no longer regulate its internal temperature effectively. These findings are relevant as many countries are witnessing longer and more intense heatwaves. The study provides fresh insight into the human body's metabolic and cardiovascular stress during heat exposure, helping health professionals, city planners, and citizens better understand the risks.
What happens to the body at 50°C? New study breaks it down
The study involved 13 healthy adult participants aged between 23 and 58, including seven women. The researchers wanted to test the upper limit of the body’s "thermoneutral zone." This is the temperature range in which the body does not need to work harder to maintain its internal temperature.
Each participant was exposed to five controlled environments. These environments varied in both heat and humidity, ranging from 28°C to 50°C and humidity levels of 25% and 50%. During the hour-long exposure, participants remained at rest while researchers monitored several key physiological indicators such as:
- Core and skin temperatures
- Heart rate
- Blood pressure
- Breathing rate
- Sweating rate
- Metabolic rate
These measurements helped scientists understand how the body responds when environmental conditions become more stressful.
Heat and humidity force the body to work harder, study finds
At 40°C, the body began to show measurable signs of increased effort to stay cool. When the humidity was at 25%, participants experienced a 35% increase in resting metabolic rate. This means the body was burning more energy even while at rest, just to regulate its temperature.
At 40°C with 50% humidity, the metabolic rate rose by 48%. Higher humidity makes it harder for sweat to evaporate, which in turn makes it more difficult for the body to cool down naturally. These findings suggest that even without physical activity, the body needs to use more energy in hot and humid environments.
Dr. Mark Guido, an endocrinologist at Novant Health Forsyth Endocrine Consultants, noted that higher humidity seems to play a significant role, as reported in Medical News Today. "In the study, there was some evidence that resting metabolic rate was higher at higher humidities, even at the same temperature," he said.
50°C heat puts your heart under pressure, study finds
At the highest test setting of 50°C with 50% humidity, the body began to struggle more visibly. Participants experienced a 1°C rise in core temperature, and their heart rates increased by 64% from the baseline. They also produced 74% more sweat compared to cooler conditions.
According to the study, this increase in heart rate is an indication of how hard the cardiovascular system must work to manage internal temperature. Dr. John P. Higgins, a sports cardiologist at McGovern Medical School, explained that people living in hot climates are often better adapted to heat and may show less of a rise in metabolic rate compared to those who are not acclimatised.
Participants at this level also showed signs of increased myocardial workload. Their hearts needed more oxygen to maintain normal function, which means the heart was under more strain. Dr. Guido explained that this could have long-term effects. "It very well could lead to an uptick in cardiovascular disease by putting more strain on the heart," he said.
Why humidity matters
One of the key observations from the study was the role of humidity. When sweat cannot evaporate due to high humidity, the body loses its main cooling method. This forces other systems like the heart and lungs to work harder, increasing metabolic demand and possibly leading to health complications over time.
Dr. J. Wes Ulm, a bioinformatic scientific resource analyst at the National Institutes of Health, noted that the body has internal mechanisms to achieve homeostasis, or balance. "The body, in general, will find ways to activate the various feedback loops needed to achieve homeostasis," he said.
But as this study shows, there are limits to what the body can handle, especially when both temperature and humidity levels rise beyond a certain point.
Hydration does not fully protect
The researchers also tested whether drinking water could help cool the body in these extreme conditions. Surprisingly, hydration did not reduce core temperature or metabolic stress. Even when fully hydrated, participants still experienced significant strain, especially at the highest heat and humidity levels.
This detail highlights that while staying hydrated is important, it is not a complete safeguard against heat-related stress in extreme environments.
Real-world implications
While the study had a small sample size of 13 participants, the results offer useful insights into human physiology under thermal stress. More research will be needed to test whether these findings apply across different populations and in outdoor or more variable environments.
However, the results align with a broader concern among health experts: rising global temperatures may pose a serious risk to human health. As cities experience hotter summers, understanding how the body reacts to heat can help governments design better warning systems, improve access to cooling centres, and guide the use of public resources during heat waves.
The findings also suggest that people in cooler regions, who are not acclimated to heat, might be more vulnerable when exposed to high temperatures. This could have implications for travel, labour safety, and public health planning.
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