Extreme heat means nights are getting warmer — and it's bad for your sleep

Extreme heat continues to grip the United States, with high temperatures expected to creep into the South and Southeast this week. Heat index values may be higher than 110 degrees in some places, according to the National Weather Service.

But while nights used to provide a welcome break from the heat, that’s often no longer the case. Research finds that nights are getting warmer — especially in North America, where data shows consistent signs of nighttime warming.

Nights aren’t just getting warmer, though — they’re heating up faster than days in many parts of the world, according to 2020 research published by the University of Exeter. The researchers found that this so-called warming asymmetry is mostly caused by changing and increasing levels of cloud cover, which retains heat at night. According to the U.S. Global Change Research Program, maximum temperatures are up to 1.66 degrees Fahrenheit higher than they were before 1960, while minimum temperatures are up to 1.91 degrees higher.

Unfortunately, all that heat can do a number on your sleep. “Our body temperature naturally falls at night, which promotes good, quality sleep,” Dr. Beth Malow, director of the Vanderbilt Sleep Division at Vanderbilt University Medical Center, tells Yahoo Life. “When it is too hot, especially at night, our body temperature doesn’t have the chance to fall — also called thermoregulation — which interferes with sleep.” In fact, one study found that hotter nighttime temperatures have made people around the world sleep an estimated 44 hours less a year in the beginning of the 21st century. If temperatures continue to rise, the study says, the effects could cause people to lose between 50 and 58 hours of sleep per person each year by the end of the century.

Here’s what sleep experts want you to know about heat’s impact on your ability to get quality sleep — and what you can do about it.

How heat impacts sleep

Sleep and temperature regulation “share real estate in the brain that is quite close to one another,” Dr. W. Christopher Winter, a neurologist and sleep medicine physician with Charlottesville Neurology and Sleep Medicine and host of the Sleep Unplugged podcast, tells Yahoo Life. “Research has shown that when temperatures are too hot, sleep quality and depth suffers,” he continues. “Less deep and restorative sleep is obtained, and the sleep is more fragmented.”

But that can do more than make you feel tired in the morning. “We need deep sleep and REM sleep for brain health,” Malow says. Research has found that hotter temperatures at night make it harder to sleep and reduce deep wave and REM sleep, which the body relies on to restore and repair itself overnight.

Lack of sleep can also impact your mood, weight control, immunity and the functioning of your heart, lungs and brain, Malow points out. Ultimately, when you don’t get enough sleep, “you cannot reset your physical and mental health in the same way that you normally do,” Malow says.

Struggling with sleep due to heat here and there is unlikely to have a major impact on your health, Winter says, but it can add up over time. “Imagine only receiving 90% of the calories and nutrients you require,” he says. “This is not an immediate death sentence, but, over a long period of time, these deficiencies will take a toll.”

There are a few things you can do for relief

Doctors say there are several steps you can take to try to stay cool overnight, whether you have air-conditioning or not.

• Turn on the AC. If air-conditioning is an option, having it running at night is key. “If you can’t afford higher levels of AC, consider using a fan,” Malow says. Keep in mind that when indoor air temperatures are hotter than about 95 degrees, using a fan may cause your body to gain heat instead of losing it.

• Reduce the thermostat temperature. If you can afford it, Winter suggests lowering the thermostat. And, if your air-conditioning seems to be doing a subpar job, he suggests having it serviced. “Sometimes getting a new or more efficient AC unit can lower both temperature and cost to do so,” he says.

• Invest in a window AC. If you don’t have central air-conditioning and are struggling to stay cool at night, consider purchasing a window AC for your bedroom. This should at least help to keep the area where you sleep cool.

• Sleep in cooler parts of your home. If your home is multilevel or you have a basement, Malow recommends sleeping on lower floors. “Heat rises,” she points out.

• Try to physically cool off. “You can put a damp washcloth on your forehead to lower body temperature before you go to sleep,” Malow says.

• Wear less to bed. Malow suggests sleeping with less clothing on and using a thinner sheet to stay cool overnight.

• Consider cooling sleep products. Cooling mattresses, pillows and bedding can help keep you from overheating at night, Winter says. Linens made of cotton, bamboo and silk are also known for being airier than others.

• Block out light. During the day, Malow recommends that you close your curtains or blinds to reduce direct sunlight. This can help keep temperatures inside your home cooler, both during the day and at night.

• Stay well-hydrated. “Make sure you are drinking lots of water during the day,” Malow says. “That will keep you from being dehydrated, which can lead to not sweating enough, promoting overheating.” The National Academies of Sciences, Engineering, and Medicine recommends that women have about 11.5 cups of fluids a day and that men aim to have about 15.5 cups daily (from liquids and food). However, you’ll likely need more than that if you’re sweating.

If you’re struggling to sleep through heat, doctors say it’s important to not be dismissive of what you’re going through — and to try to take steps to stay comfortable. “Sleep affects every aspect of our health,” Malow says. “Think of sleep as a reset button that keeps our physical and mental health in check and functioning normally.”