I am a radiator-hugging hater of being cold. It makes me tense and tetchy. But what if you are in your house, heated to 18C (64F), wearing a scarf so long and fluffy that it wraps around you four times and buries your chin, and you are still chilly? What if you are the one in the office always huddled under a shawl, blue-nosed, while everyone else goes about their business in T-shirts?
Clearly, these situations pose no threat to maintaining a core body temperature of about 36.5C. In 1970, fewer people had central heating, and the temperature of the average British home in winter was 12C. As much as I appreciate my gas boiler, the sound of it revving up to burn more fossil fuel has come to represent climate-crisis doom. I aspire to feel cosy at 12C. Can I ever become one of those rosy-cheeked hardy types who pop to the corner shop in flip-flops in February?
According to Christopher Minson, a professor of human physiology at the University of Oregon, there is hope. “Absolutely, people can adapt progressively to cooler temperatures,” he says. “Humans have become very thermostatic. We go from our perfectly heated or air-conditioned house to our perfectly heated or air-conditioned cars to our perfectly heated or air-conditioned work.” This, he believes, is not healthy. We’re not exercising the mechanisms we use to keep warm, and our perception of acceptable temperatures has become unnaturally narrow.
Essentially, says Minson, humans are big bags of water and meat. “What keeps us warm, really, is our metabolic rate: how much energy we’re producing.” But there are physiological differences meaning that some have to work harder than others to maintain their core temperature.
“Men in general are going to have a bit more muscle mass than women,” says Minson, “so this helps them stay a little warmer.” This is because having more muscle increases your basal metabolic rate – your capacity to burn energy from food. It helps explain the modern phenomenon of “sexist” office air-conditioning, whereby the temperature is perfect for most men, but chilly for most women.
There are always exceptions, and other reasons why some people feel the cold more than others. Age is a big factor because the older we are, the lower our metabolic rates tend to be. But we all have thermoreceptors, says Minson. “Throughout your body – your skin, your muscles, your organs and your tissues – they are feeding information back to your hypothalamus, which is where your big central regulator of temperatures is.” Even if the blood in that area is 36.5C, signals coming in saying that the temperature has dropped are seen as a threat. This triggers vasoconstriction in the skin, to minimise the heat from our warm blood being lost to the outside world. In response, we curl up and bring our arms close to our bodies and put more layers on.
It is possible to train ourselves out of our thermostatic ruts, and Minson is constantly experimenting on himself. As it got colder one winter, he wore progressively warmer jackets to cycle to work. “I still saw people wearing just a T-shirt,” he says. So, one day, he decided to copy them. “The first few days were like: ‘Wow, it’s really cold,’ but within less than a week it got easier, and after a couple of weeks I could ride with my arms exposed and not feel as cold.”
Minson is a big fan of cold blasts in the shower, too. He started out by turning the shower to cold for 15 seconds, then increased it to 30 seconds until he could tolerate what he calls enthusiastically, “a one-minute cold blast. It’s miserable for a while, but you do adapt. After doing that for a month or two, I started finding that when I was in cold environments I felt less cold.”
He puts this acclimatising effect mostly down to an adjustment in our cold-threat perception. “The thermoreceptors in your skin are now telling your brain this is not a threat – you’re going to be OK.” The precise mechanics of this haven’t been sufficiently demonstrated, but a fair assumption would be that “the firing rate of those thermoreceptors has decreased. Certainly, the perception of what those neural firings mean would be viewed as less of a threat to our standard body temperature.”
A second benefit is that the exposure to cold stressors trains the body to keep warm more effectively, “maybe increasing metabolic rate or having better vasoconstriction”, says Minson. The walls of blood vessels are muscular, and leading thermostatic lives doesn’t exercise them. “If you’re not stretching those muscles to constrict and dilate, then it’s possible that they’re not as healthy.”
An obvious cause of my chills is sitting down to work for hours, moving only my eyes and fingers. If I did 45 minutes of exercise before sitting down, this could keep me warmer for about two hours, says Minson. And, of course, putting on more muscle mass would raise my basal metabolic rate, which would also keep me warmer.
Eating also raises your metabolic rate for a few hours, to help with digestion. Some foods have more “thermic effects” than others, though. “Fats and proteins in particular will generate more heat,” says Minson, “than simple sugars that are easily digestible and taken right into your bloodstream.”
Minson also suspects that the materials you wear can make a difference. “Human skin can perceive wetness or dampness,” he says. This exacerbates the sense of cold-threat, so he says: “Wearing more natural, woolly fibres help wick the water off our skins.” Essentially, however, we need to toughen up and turn our thermostats down, but that’s easier said than done. One of the main take-homes from Minson’s years of research into thermoregulation is that: “People really don’t like being cold.”