When it’s hot enough to cook an egg on the bonnet of a car, do you hide indoors or embrace the heat? People have different levels of heat intolerance and tolerance, which is their ability to physiologically adjust to heat stress exposure. It's influenced by numerous factors, including your DNA. An AncestryDNA^® + Traits test can tell you how your genetic markers are influencing your sensitivity to heat.

Why Are Some People More Tolerant of Heat?

Scientists have long been fascinated with humans’ ability to tolerate heat. Humans have unique physiological adaptations, such as the ability to sweat, which increase heat tolerance. But that’s not all they have going for them. People can also adjust to different environments and improve their heat sensitivity accordingly. This process is called acclimatisation.

Through acclimatisation, you can train your body to react quicker and more efficiently to heat. This may be of particular interest if you’re moving or spending time in a hotter climate. Actions that can help include:

• Spending a limited time performing in the heat (such as exercising or playing a sport) and then giving yourself a cooldown. By repeating this process a few times daily, you can slowly improve how your body reacts to the heat. These actions are built-in to some outdoor professions, such as construction and post delivery—both of which may require higher than average heat tolerance.
• Staying hydrated while exposed to high temperatures. This is a critical component of helping to shift your heat intolerance to tolerance. When you become dehydrated, your body can't sweat enough to reduce your core body temperature, which can potentially cause heat stroke if left unmanaged.

Studies have found that work-related performance—like the ability to focus and excel at the task at hand—declines in hotter temperatures, as the body works harder to regulate your temperature. One review of Major League Baseball players' performance revealed that when temperatures rose above 95 degrees Fahrenheit, umpires' accuracy decreased. The good news is that the body seems to adjust relatively quickly. A study of tennis players found that high temperatures negatively impacted players' first games but not their second games.

The Genetic Influence on Heat Tolerance

Interested in how genes influence a person’s heat tolerance, the AncestryDNA^® team asked over 237,000 people, "How well do you tolerate heat?" Their answers were then compared with their DNA, revealing over 445 DNA markers connected to heat tolerance.

After identifying the relevant genes, AncestryDNA scientists calculated a polygenic risk score, which is used to predict your likelihood of having increased heat tolerance based on your unique DNA. In doing this, the team determined that genetics only play a small role in how well people tolerate heat—around 5% of the differences in heat tolerance can be explained by genetics. This reinforces the importance of environmental factors, such as where you live and how you have acclimatised, for developing heat tolerance.

What Else Does Science Say About Heat Tolerance?

Several factors influence your body’s ability to manage heat sensitivity outside of genetics, including age. One study compared the reactions to heat stress of young (ages 19-27) and older (65-77) adults, revealing that older adults had a diminished tolerance to heat. Conversely, infants and younger children are also more susceptible to heat stress.

A 15-year nationwide study reviewed heat exposure and hospitalisation in Brazil from 2000-2015, revealing that as the outside temperature increases, so do hospitalisation rates. Notably, Children under the age of 5 and adults 60 years or older were the most susceptible—suggesting extra precautions for heat protection need to be taken in these populations.

Mental health can also be impacted by heat exposure. As external temperatures rise and heat stress increases, mental health can decline. Chronic heat stress may increase anxiety, stress, and cognitive impairment, especially in the young, old, and those who have preexisting mental health conditions.

Interesting Facts About Heat Tolerance

While the human body is capable of adapting to heat over time, cultural attitudes about thermal perception—how a person or group of people view their heat sensitivity—can play a role, too. For example, those who live in warmer or cooler places may feel differently about 75°F (about 23°C) weather. Some may think that’s a bit on the warm side, while others would see it as refreshingly cool.

Outside of human adaptation to heat tolerance, scientists have long been fascinated with tolerance amongst other species. The genes that confer increased tolerance in plants and non-human animals (such as cows) have significant implications for global agricultural industries and are a major focus of scientific endeavours.

Wondering why you're always hot or feeling like your body's overheating? You may not have the DNA markers associated with heat tolerance, or you may not be acclimatised to deal with higher temperatures. Take an AncestryDNA^® + Traits test to see what your DNA indicates. If you've already taken a test, your Ancestry^® membership gives you access to your results for heat tolerance and other performance-related traits like heart-rate recovery and physical agility.

 

References

“Acclimatization.” The National Institute for Occupational Safety and Health. Accessed July 26, 2024. https://www.cdc.gov/niosh/topics/heatstress/acclima.html.

“Extreme Heat Affects Early Childhood Development and Health.” Center on the Developing Child, Harvard University. January 2024. https://developingchild.harvard.edu/heat-paper/.

Fesselmeyer, Eric. “The impact of temperature on labor quality: Umpire accuracy in Major League Baseball.” Southern Economic Journal. July 7, 2021. https://doi.org/10.1002/soej.12524.

Hanna, Joel M. and Daniel E. Brown. “Human Heat Tolerance: An Anthropological Perspective.” Annual Review of Anthropology. 1983. https://www.jstor.org/stable/2155648.

Kenawy, Inji and Hisham Elkadi. “Effects of cultural diversity and climatic background on outdoor thermal perception in Melbourne city, Australia.” Building and Environment. May 15, 2021. https://doi.org/10.1016/j.buildenv.2021.107746.

Matteo Picchio, and Jan C. van Ours. “The impact of high temperatures on performance in work-related activities.” Labour Economics. April 2024. https://doi.org/10.1016/j.labeco.2024.102509.

Racinais, Sebastien and Julien D. Périard. “Benefits of heat re-acclimation in the lead-up to the Tokyo Olympics.” British Journal of Sports Medicine. April 2020. https://doi.org/10.1136/bjsports-2020-102299.

Rony, Moustaq Karim Khan, and Hasnat M Alamgir. “High temperatures on mental health: Recognizing the association and the need for proactive strategies-A perspective.” Health Science Reports. December 4, 2023. doi:10.1002/hsr2.1729.

Wolf, S. Tony, Rachel M. Cottle, et al. “Heat stress vulnerability and critical environmental limits for older adults.” Communications Earth & Environment. December 18, 2023. https://www.nature.com/articles/s43247-023-01159-9.

Zhao, Qi, Shanshan Li, et al. “Geographic, Demographic, and Temporal Variations in the Association between Heat Exposure and Hospitalization in Brazil: A Nationwide Study between 2000 and 2015.” Environmental health perspectives. January 8, 2019. https://doi.org/10.1289/EHP3889.