A reader named Gunjan recently asked a question about trouble sleeping due to temperature changes at night. Here it is, lightly edited:
“It seems my body is very sensitive to temperature while I am sleeping. Many times it has happened that I went to bed at an optimal temperature. But as soon as my body sleeps, I wake up feeling too cold. Then I go to bed after switching off the fan or covering myself with the bed sheet but then I can’t sleep because I’m too hot. This is quite frustrating. . . . Does anybody . . . have any help to offer?”
Insomnia and Thermosensitivity
Insomnia may have something to do with compromised thermoregulation, but the issue has not been fully investigated, say authors of a paper on sleep and thermosensitivity. Evidence shows that older adults may have an impaired ability to recognize the most comfortable temperature for sleep, and this may relate to abnormalities in the area of the brain that evaluates comfort. Not much else is known.
But I’m never surprised when people complain of trouble sleeping related to temperature sensitivity. I have the problem myself. I’ve gone to bed in very hot and very cold situations and lain awake for a good chunk of the night. Like Gunjan, I regularly have to make small temperature-related adjustments in the middle of the night. Now, with some nights warm and others cool, is the season when it’s trickiest to get it right.
Temperature Changes at Night
Core body temperature varies by about 1.5 degrees Fahrenheit over the course of the 24-hour day. From a temperature high in the evening, it descends and reaches its low point some 1 to 3 hours before normal wake-up time. If you keep the bedroom windows open at night (a cool bedroom is good for sleep), the room temperature will likely drop as well. The combination of internal and environmental temperatures falling could easily explain why you might wake up feeling cold at night.
Covering yourself with a blanket or a bed sheet is the obvious way to make yourself comfortable enough to get back to sleep. But what if, like Gunjan, you then feel too hot?
Covering up can create a closed system where, once the skin temperature has risen enough to dilate the blood vessels close to the skin, the body heat then released has no place to go. It’s similar to the situation created by an electric blanket. The blanket continues to add heat to the body, increasing skin and core body temperatures. The heat the body would normally throw off is then trapped underneath the blanket. You wake up feeling too hot to sleep.
Here are two ways to keep from overheating at night:
- Use sheets and blankets made of a breathable fabric such as cotton. Fabrics like polyester are more likely to trap heat rather than allow for its release.
- When you cover up, see if keeping your feet outside the covers helps. You lose lots of heat through your extremities, so keeping them uncovered, or partially covered, may make you comfortable enough to sleep through the night.
Help for Sleep Onset Insomnia
It’s easier to go to sleep when core body temperature is falling, and people who have problems falling asleep—sleep onset insomnia—may have trouble cooling down at night.
Ideally, the temperature in the bedroom should be a little lower than is comfortable during the day. But there are also ways to facilitate internal heat loss. Activities that increase skin temperature eventually help to cool you down. Warming the skin dilates blood vessels close to the skin. This enables the release of body heat and a lowering of core body temperature to occur for a few hours after the activity ends, in turn facilitating sleep.
Early in the evening these activities may trigger processes that help you fall asleep:
- Take a hot shower or bath
- Spend time in a sauna
- Do a resistance workout or aerobic exercise
As you’re winding down on cooler nights, mild heating of the hands and feet may dilate the blood vessels enough to facilitate heat loss, lowering your core body temperature and inducing sleep. But this is a losing strategy on the warmer nights. Lightly clad and barefoot is the way you want to be.
If you’re sensitive to temperature changes at night, what have you found that helps?