For the study, 31 healthy people slept in either a 75-degree room or a 66-degree room. Researchers found that the colder sleepers burned more than 7 percent more calories than the warm sleepers—likely because their bodies were working to raise their core body temperature to a stable 98.6 degrees, says study author Francesco Saverio Celi, MD, MHSc, of the National Institute of Diabetes and Digestive and Kidney Disease.
If you lowered the thermostat to 66 degrees at bedtime, you could burn an extra 100 calories over the course of 24 sleeping hours, according to study results. That might not sound like much, but it adds up—in theory at least.
See, researchers don’t yet know whether your body compensates for these calories in another way—like by making you hungrier or less amped to work out when you’re awake, says Celi. Still, if you’re trying to lose a few pounds, it can’t hurt to turn down the temperature before you crawl under the covers. Just make sure you don’t pile on the blankets or wear your warmest pajamas at the same time: You can’t expect to see results unless you tough it out in the cold, says Celi.