Why You Should Sleep in a Cool Bedroom

CC BY 2.0. diastéme

Turn down the thermostat, crack a window, and ditch the blankets for some science-backed health benefits.

On cold winter nights, my husband and I often have the same argument: I want the window open, he wants it closed. I think it’s because he grew up in a house where the thermostat always stayed at 21 Celsius (70 F), whereas mine had a wood-burning cookstove in the kitchen that heated downstairs but left the rest of the house feeling like an ice box.

If research turns out to be accurate, then my preference is the healthier one. Scientists are now surmising that humans’ lack of cold exposure could actually be harming us. We spend our lives in climate-controlled spaces, where the temperature doesn’t fluctuate much year-round. If it does get cool, we rush to turn up the heat or put on a sweater, so as not to experience any physical discomfort.

While the idea of temperature stability may sound pleasant, some scientists think that the human species has not yet evolved to cope with it. This is called the ‘Metabolic Winter’ hypothesis, proposed by NASA scientist Ray Cronise, Harvard geneticist David Sinclair, and Andrew Bremer of the National Institutes of Health. It suggests that, after spending millions of years chasing after warmth, the fact that we now have it on demand is wreaking havoc with our bodies and is contributing to obesity.

“Seven million years of human evolution were dominated by two challenges: food scarcity and cold. ‘In the last 0.9 inches of our evolutionary mile,’ [Cronise, Sinclair and Bremer] write, pointing to the fundamental lifestyle changes brought about by refrigeration and modern transportation, ‘we solved them both.’ Other species don’t exhibit nearly as much obesity and chronic disease as we warm, overfed humans and our pets do. ‘Maybe our problem is that winter never comes.’” (The Atlantic)

It’s an interesting concept that we’ve explored before on TreeHugger – that of ‘brown fat,’ a.k.a. brown adipose tissue, that burns off excess fat, rather than storing it like regular fat. Brown fat, however, must be activated by cold temperatures in order to work effectively, which is why it’s often lost when we keep cozy all the time.

So, back to the bedroom debate: It appears that sleeping in a mildly cold bedroom (55-65F / 13-18C range) is beneficial because it “increases body energy expenditure without shivering and without compromising our precious comfort.” The key is not to shiver excessively, because that would affect one’s quality of sleep, but to find the right balance of pajamas, blankets, and thermostat to achieve roughly 65 F (18 C) in the bedroom and 90 F (30 C) on your skin’s surface. Markham Heid explains for TIME Health:

“If that sounds nuts to you, consider the fact that thin pajamas, plus a sheet and blanket, could crank up your skin temperature to that 90-degree range – even if your room of slumber is only 65 degrees. On the other hand, if your bedroom is too chilly or your blankets aren’t thick enough, blood vessels in your skin can narrow, locking in heat and upping your core temperature to a point that your sleep is disturbed.”

Ray Cronise urges people to try to wean themselves off blankets as much as possible, something that sounds nightmarish but he insists is not miserable, “once you’ve gone through withdrawal and adapted to it.”

“Like eating sweets and turning up the heat, [Cronise] sees sheeting and blanketing as acquired habits that can be changed. He was able to wean himself from blankets gradually, by learning to sleep with them first folded down partway, and then folded further, and then, eventually, all the way down to his feet.”

Cooling the bedroom also acts as a signal to the brain that it’s time to sleep, making it easier to nod off. This is why some insomniacs use cooling caps on their heads and many of us enjoy the feeling of a cold pillow.

So, if you’ve got some extra pounds to lose or are struggling falling asleep at night, think about giving cold a chance. Switch out your comforter for something a bit thinner, choose some lighter PJs, turn down the thermostat a few degrees at a time, and, of course, open that window a crack. You might be pleasantly surprised by the results.