During the summer, the last thing many of us think about drinking is a hot beverage. Instead, we reach for sodas, iced drinks, or snow cones because we want to cool off. However, in some areas of the world, people choose hot drinks on hot days to cool down. Despite how strange it sounds, evidence suggests hot drinks may be better at cooling people off on hot days than you might think.
One of the best sources supporting the idea of hot drinks cooling people off on hot days is a study from Ollie Jay, the current director of the Thermal Ergonomics Laboratory at the University of Sydney. In 2012, he was an associate professor at the University of Ottawa in Canada, where he decided to perform a study to discover the true effectiveness of hot drinks on cooling a person down. The results of the study confirmed that hot drinks do, in fact, cool people off. However, there are some minor caveats.
In the study, Jay and a team of researchers carefully observed nine cyclists for 75 minutes. A fan would blow on the cyclists, ensuring that their sweat would evaporate. Throughout the study, the men would drink water that ranged in temperatures from 35 degrees to 122 degrees Fahrenheit. Then, Jay and the researchers compared the energy lost in the form of heat from the cyclists. The results were straightforward. While drinking hot water, the cyclists lost 56 kilojoules more of energy in comparison to room temperature water. However, cold water caused the subjects to gain 21 kilojoules of energy. Essentially, this means that hot water cooled the cyclists off significantly more than cold water, and that cold water may actually cause a person to retain heat.
Though many people may find the results of the test paradoxical, there is a logical reason that hot drinks on hot days are effective at cooling people off. With the exception of individuals with conditions that prevent it, every person sweats. It is an integral process of the human body that helps maintain body temperature and prevent overheating. When we sweat, heat causes the sweat to evaporate, thus cooling us. Hot drinks trigger the body’s sweat response and cause us to sweat more, resulting in more cooling. Cold drinks may inhibit the sweat response, leading to higher temperatures.
Every gram of sweat that evaporates from the skin is a loss of around 2.43 kilojoules of energy in the form of heat. In the study, the men who drank hot water gained 52 kilojoules of heat from their water. After sweating, the men lost 108 kilojoules of heat for a net loss of 56 kilojoules. The cold drinks cooled the men by 138 kilojoules. Because the men sweated less as a result of the cold drink, they retained a total of 159 kilojoules of heat. Room temperature water caused them to lose roughly the same amount of energy through sweat that they gained through drinking the water.
Now that we know why hot drinks on hot days cool us off, many people may wonder why hot drinks cause us to sweat more in the first place. Ollie Jay wondered the same thing, so he ran a new experiment in 2014. In this test, he had some volunteers gargle water of varying temperatures. At the same time, he injected water directly into the stomachs of other volunteers through a nasogastric tube so the water wouldn’t touch their mouths. The results found that gargling water didn’t change sweat levels, but stomach injections did.
Both the stomach and the mouth contain thermoreceptors that respond to heat and then control sweat levels. The results of the test suggest that stomach receptors are significantly more responsive or controlling than mouth receptors. If the stomach senses heat, it makes the body sweat. This is why hot drinks cause us to sweat more. Additionally, this suggests that drinks are not the only heated options beneficial on hot days.
Many people don’t enjoy hot beverages or are not capable of drinking them for a variety of reasons. Professor Peter McNaughton from the University of Cambridge suggests possible alternatives to hot drinks on hot days. Peppers are common in spicy and hot foods because of their active component, capsaicin, which triggers the same thermoreceptors that hot drinks do and results in a similar sweat response. This means that spicy foods such as chili may be as effective as hot drinks on hot days.
Though the results of the tests seem conclusive, Ollie Jay does warn against flippantly drinking hot drinks on hot days. The experiment occurred while the cyclists had a fan blowing on them, which guaranteed their sweat would evaporate. However, many factors may prevent sweat from evaporating, which would also prevent the cooling effect. Humidity, wind speed, clothing, and excess sweating may all reduce the cooling effect of hot drinks.
Some ideal conditions guarantee the effectiveness of hot drinks on hot days. Primarily, the temperature should be hot enough to cause sweat to evaporate. The humidity level should also be fairly low. Thick clothes or clothes that cover too much of the body will absorb sweat before it can evaporate and diminish the cooling effect. Some people naturally sweat more than others. If a person sweats too much, their sweat may drip off of their body and will not provide any cooling.
Another factor to consider is the temperature of the drink. You might think the hotter the drink, the greater the cooling effect but, while true in theory, there are some risks in actual practice. The most notable risk of excessively hot drinks is of burns. Hot beverages are dangerous, particularly to the tender tissue of the tongue and throat. In addition, the International Agency for Research on Cancer has found that drinks over 149 degrees Fahrenheit are possible carcinogens and may lead to cancer. Most people don’t consume drinks such as coffee, hot tea, and hot chocolate at this temperature. However, some machines do prepare the drinks at temperatures higher than 149 degrees because they expect some level of cooling.
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