Phun Physiology: Does a hot drink cool better than a cold one?

The Cup of Tea, ca. 1879. Mary Cassatt (American, 1844–1926)

 Oil on canvas (Wikimedia public domain)

Now that the dog days of summer are chasing my wheels, I decided to research an astonishing claim I recently read on a cycling listserv about keeping cool. I’ve included links to references for the interested reader.

My search led me to not one but two popular-press articles published a year ago asserting that a cup of hot tea could cool cyclists better than a cold beverage. If there is any merit to the claim, then American cyclists ought to institute afternoon tea not just for propriety, but also for safety and performance.

A team of researchers at the University of Ottawa made the remarkable discovery that drinking a hot beverage triggers a sweat response which is more than able to compensate for the warming effect of the hot beverage.

The finding begs the question of whether turning on the sweat spigots leads to greater cooling in all cases. The lead researcher, Ollie Jay, notes that the cooling effect of drinking a hot beverage does not hold in all situations. He states:

The caveat is that your sweat must fully evaporate in order to produce the desired cooling effect. If you’re exercising hard, or wearing too many clothes, or in a very humid environment, you may produce sweat more quickly than it can evaporate, in which case it’s no longer desirable to ramp up your sweat rate further.

The tell-tale sign of producing too much sweat? When beads of sweat drop to the ground. At this point, evaporative cooling is not occurring. And there is no advantage to increased sweating. Jay states, “if the sweat’s not going to assist in evaporation, go for a cold drink.” Jay notes,

[I]f you’re in a humid locale—for example, anywhere on the East Coast—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.

Other studies support the intuitive notion of drinking cold beverages to stay cool. One study by Lee and Shirreffs (2007), for example, reports that at 25.4C [77.7F] and a relative humidity of 61%, exercising cyclists who drank cold beverages had significantly lower skin temperatures and lower pulse rates than cyclists who drank warm fluids.

Yet another study by Burdon et al. (2010) conducted at 70% relative humidity and 28C [82.4F] reveals that

Consumption of cold beverages during prolonged exercise in the heat improves body temperature measures and performance.

This team of researchers postulated,

Beverages consumed by athletes exercising in the heat should perhaps be cold for performance and safety reasons.

In sum, it is probably safe to assume that the heat and humidity of North Carolina summers warrant cold drinks all around, especially if you are working hard! 

What’s your cup of tea?

Let’s ride!