by James Hunt
When it's hot outside, few things are more inviting than a tall glass of ice-cold water—unless you're my grandmother, who swore that the best way to cool down on a hot day was to drink a piping hot cup of tea.
You've probably heard other people say the same thing, but is it just an old wives' tale, or is there any truth in it? If you're trying to stay cool, should you reach for the fridge or the kettle?
Common sense suggests that ice water would be the better option. Getting a near-freezing cold beverage into your body should lower your core temperature and offer temporary respite from the blazing heat around you. That's just physics: cold water naturally draws heat from the warmer body tissue around it.
Although some people suggest that the body responds to a cold stimulus by trying to heat up, there's no real evidence for any real effect from that.
But the evidence for drinking hot beverages to cool down isn’t straightforward either, suggests research from the University of Ottawa. At least one study found that drinking even a small hot drink triggered a disproportionately high sweat response without significantly raising your core temperature. And since sweating cools you down, that means a hot drink is actually better at cooling you down than a cold one.
Of course, there are some catches. One is that you won't feel the effects until your sweat has evaporated fully, contrasting with the instant effect of an ice water hit. The other, much bigger one is that it only works under certain conditions. If it's humid, if you're sweating a lot already, or if you're wearing clothes that trap moisture on you then there's bad news: drinking a hot drink is only going to make you hotter.
The ultimate explanation for this phenomenon was provided by Peter McNaughton, a professor of pharmacology at King's College London. His research revealed that the TRPV1 heat receptors in your tongue and throat react to heat stimuli by causing you to sweat, regardless of your core temperature. These heat sensors are actually the same reason you break out in a sweat when you eat spicy foods.
So while it seems counterintuitive, having a hot drink on a hot day actually can cool you down. Turns out my grandmother knew better than all of us. Let's raise a steaming mug of tea to her memory.