Drinking liquids in hot weather to cool down: should we drink cold or hot beverages?

Drinking liquids in hot weather to cool down: should we drink cold or hot beverages?

In the past week, we experienced a few days of nearly insanely hot days, peaking on Tuesday July 19, the day one of the most famous walking events , the Vierdaagse in Nijmegen was supposed to start. 
Was supposed, because the temperatures that were expected to hit 40°C were deemed to be too dangerous for a strenuous walking day in which fit adult men are expected to cover a distance of 50 kilometres while others are still required to walk for 40 km.
Since the event was cancelled in the past two years due to COVID and had been cancelled as well a few years earlier due to a casualty of heat stroke, the organizers did not want to take any risks. 
 
And risk there indeed is. While younger people may be able to regulate their own body heat better, this particular walking event attracts more senior citizens than any other walking event due to its history as an event celebrating the liberation of the Netherlands and Nijmegen in particular. 
 
Of course we all know one should also hydrate well when exercising and even moreso during heat. Traditionally most people will want to drink a refreshing cold drink, eat ice cream and will prefer a cold salad over hot food when it is sweltering hot outside. 
 
So, imagine my surprise upon hearing in a science-oriented podcast we may be better off drinking hot tea, rather than cold drinks! 
How can this happen? Drinking hot tea might cool you more since the brain may respond to hot drinks by cooling you down more than a cold drink can! 
 
This actually does make sense when you come to think about it, and actually has been a habit in many countries around the world with sweltering hot summer, where conventional wisdom says that you can cool down on a hot day by drinking a hot beverage.
 
Here follows the explanation 
 

Why and how drinking a hot beverage can cool you down

Put briefly, yes, a hot drink can cool you down, but only in specific circumstances. 
Ollie Jay, a researcher at the Thermal Ergonomics Lab from the University of Ottawa, explains:  
“If you drink a hot drink, it does result in a lower amount of heat stored inside your body, provided the additional sweat that’s produced when you drink the hot drink can evaporate.”
 
How does this work? “What we found is that when you ingest a hot drink, you actually have a disproportionate increase in the amount that you sweat,” Jay says. “Yes, the hot drink is hotter than your body temperature, so you are adding heat to the body, but the amount that you increase your sweating by (if that can all evaporate) more than compensates for the added heat to the body from the fluid.”
 
The increased rate of perspiration is the key. Although sweat may seem like a nuisance, the body perspires for a very good reason. When sweat evaporates from the skin, energy is absorbed into the air as part of the reaction, thereby cooling the body. A larger amount of sweat means more cooling, which more than counteracts the small amount of heat contained in a hot beverage relative to the entire body.
 
The caveat, though, is that all that extra sweat produced as a result of the hot drink actually has to evaporate for it to have a cooling effect. 
“On a very hot and humid day, if you’re wearing a lot of clothing, or if you’re having so much sweat that it starts to drip on the ground and doesn’t evaporate from the skin’s surface, then drinking a hot drink is a bad thing,” Jay says. “The hot drink still does add a little heat to the body, so if the sweat’s not going to assist in evaporation, go for a cold drink.”
 
Jay’s team got to the bottom of the “hot drink” tip by rigorously testing the idea on cyclists in a lab. 
 
Each cyclist was equipped with skin temperature sensors and a mouthpiece measuring the amount of oxygen consumed and carbon dioxide produced, which indicated the amount of heat produced by the body’s metabolism. The researchers also carefully tracked the air temperature and humidity, among other factors. The data yielded an overall picture of how much heat each cyclist produced and how much each released to the environment, and those drinking hot water (roughly 50°C) stored less heat in their bodies than the others.
 
The researchers are still unsure why hot drinks lead the body to produce more sweat, but they have an idea. “It’s commonly thought that the hot drinks raise your core temperature, but we found that that isn’t the case,” Jay says. “What we think is that it’s the thermosensors that line the throat and mouth that elicit the additional sweating response.” He notes that additional research is needed to pinpoint the exact location of these sensors.
 
To be clear, the tip only works in very specific circumstances: a hot, dry day, where you’re not wearing so much clothing that your sweat is prevented from easily evaporating. 
In other words, if you’re in a humid area, as is the case for American states on the east coast, such as Florida, don’t try drinking hot water. But on a hot day in the desert, a cup of hot tea might actually be the trick to help cool you down. 

Best approach in hot weather

Overall, the lesson learned is that in hot, dry conditions, drinking hot drinks will cool you down, but if you’re in a humid location, it’s best to stick to cold beverages such as iced tea or non-alcoholic beer (alcohol is not a good idea!) 
In addition to the fact that hot drinks can cool down the body more than they warm it up, this also applies to spicy food because the body will also respond by sweating more profusely.
 
Our own observation as avid sauna users is that in such weather conditions it can also be beneficial to visit a sauna for the same reasons, provided you drink more (cold) liquids afterwards. 
One other caveat is how the experiment was conducted with young and healthy males who also exercised on a stationary bike at the same time. Women as well as older people may respond differently, so it seems smarter to simply abstain from heavy exercise in high heat, rather than look for methods to cool down slightly faster by means of warm versus cold beverages

Loss of electrolytes on a hot day

Another factor to take into consideration when sweating profusely due to exercise on hot days is how we don't just lose water, but also lose salts, which are mostly referred to as electrolytes. 
 
Maintaining a relatively constant body temperature proves essential to your health: an abnormally high or low body temperature diminishes organ function and can even cause death. As a result, your body has developed methods to regulate your temperature, so you can stay cool on a hot day and vice versa. 
Sweating on a hot day helps cool your body, because the evaporation of sweat releases heat from your skin. However, prolonged exposure to heat on a hot day can lead to excessive sweating and places a strain on your body due to the loss of certain electrolytes, more specifically sodium, potassium and chloride.

Importance of electrolytes

Electrolytes in your body support a number of functions. Your nerve cells use sodium and potassium electrolytes to transmit signals throughout your nervous system, and also use these electrolytes to communicate with your muscles. In addition, electrolytes regulate your blood pressure and blood volume, helping to support the proper circulation of oxygen-rich blood throughout your body.

Symptoms

Electrolyte loss and dehydration from sweating in hot weather can potentially lead to heat cramps that primarily affect large muscle groups in your legs, such as calf muscles, quadriceps or hamstrings. 
If the electrolyte loss occurs in concert with heat exhaustion, you might notice other symptoms related to heat exposure. Heat exhaustion is characterized by heavy sweating, dizziness, nausea, headaches and fatigue. You might also notice an elevated heartbeat or muscle cramping.

Prevention

You can prevent electrolyte loss by replenishing the fluid and electrolytes (sodium, potassium and chloride) lost throughout the day and by minimizing the amount of electrolytes you lose. 
Sports drinks replace essential electrolytes as well as fluid, but often also contain large amounts of processed sugar. You can avoid the added sugar by consuming natural electrolyte-rich fluids such as coconut water, harvested from the centre of young, green coconuts. Look for salt-enriched coconut water. Choosing electrolyte-rich drinks, instead of plain water, also can help prevent heat exhaustion.
 
Minimize your electrolyte and fluid loss by avoiding lengthy exposure the sun on hot days. Stay inside during the hottest hours of the day (usually between 10 a.m. and 2 p.m.) or, if you must go outside, stay in the shade. You should also limit your physical activity to minimize sweating. Save your outdoor exercise for early or late in the day, when it’s cooler, or take your workouts indoors.
 

Treatment and warnings

If you suspect you’ve developed heat exhaustion or developed severe electrolyte loss, and you're suffering from severe cramping or light-headedness, or a rapid heartbeat, seek immediate medical attention. A doctor can monitor your hydration level and electrolyte balance, and administer the appropriate intravenous fluids.
 
You should never drink large amounts of plain water after profuse sweating, especially if you have already developed some symptoms of heat exhaustion. Adding more fluid to your system without also adding electrolytes might lead to a more severe electrolyte imbalance.
 
To determine your approximate fluid needs, it is recommended to weigh yourself before and after exercise on a hot day and to make sure you are replenishing with as much fluid as is needed to weigh the same as before exercise. When you always sweat profusely during exercise, it is a good day to do the same on regular days.