The temptation to sip a hot cappuccino or tea when the mercury drops seems nearly universal. But does pouring a steaming beverage into your mouth actually increase the body’s temperature, or does it just feel that way?
One expert, Alan Hedge, director of the Human Factors and Ergonomics Laboratory at Cornell University, in frigid Ithaca, N.Y., explains why a cup of joe may not be ideal for freezing days and what the Mongols drank to survive winter invasions.
The body is armed with two ways to respond to the cold, says Dr. Hedge, who teaches in Cornell’s department of design and environmental analysis. One is the concentration of the organs in the torso, which the brain works hard to keep around 98.6 degrees Fahrenheit. When a person feels cold, the brain will tell the body to shiver, thus generating heat.
The vascular system can also move warm blood to what Dr. Hedge calls the shell of the body, such as the skin and limbs. “The shell can deal with a wider range of temperatures than the core, going all the way from getting frostbitten to getting burnt,” he says.
Most of the time, people are warmer than their surrounding temperatures, giving off heat to the environment. In colder weather, shivering generates body heat that gets delivered primarily to the core, sacrificing heat to the toes and fingers.
However, if you sip a beverage that’s warmer than your core temperature, you can feel the heat move through your body, the professor says. As long as that drink is between about 98.6 and 115 degrees (which can burn), the body should feel warmer by about 2.6 degrees, according to one study.
Another small study showed that participants who held a hot drink in a cup judged a target person as having a more generous, caring personality than those participants who held a cold drink, suggesting that feeling warmer can make a person act more warmly.
Beware the Caffeine
Although coffee or black tea is the typical go-to for many winter-bound Americans, the caffeine in them is a diuretic, “which will encourage you to urinate, which is another way to lose heat, because that fluid is much warmer than the surroundings,” Dr. Hedge says.
Neither does he recommend alcoholic drinks like hot toddies. Alcohol, another diuretic, may dilate the blood vessels, thus creating a warming sensation. “But those blood vessels are taking blood from the extremities,” he says. He points to alcohol as a large contributor to the 1,000 or so annual U.S. deaths due to hypothermia.
The Milky Way
If it’s very cold out, having a thermos filled with a hot, decaffeinated beverage like herbal tea or even water will help keep the body temperature at a comfortable level. However, Dr. Hedge says, those drinks offer no calories to generate yet more heat.
He says the ideal liquid for fighting winter chills is a warm, milky beverage like hot cocoa or a decaf latte: “The calories that most quickly convert to heat come from fat,” he says. He points to people who live in the Himalayas who drink a hot beverage made from yak butter during the long winter, and even to Mongolia during the reign of Genghis Khan.
“The Mongols drank fresh, warm mare’s milk, which gave them the ability to have a sustained, warm, high-caloric diet that kept them warm,” Dr. Hedge says.
For those who cannot stomach milky drinks, stick with something between 98.6 and 115 degrees, with no caffeine. “Try camomile tea and hopefully your core will stay warm,” says Dr. Hedge. Or just put on another sweater.
Appeared in the December 6, 2018, print edition as ‘How Much Do Hot Drinks Help in the Cold?.’