Heat and Sleep

The rising nighttime temperatures that come with climate change could mean poorer sleep for millions, a new study suggests.

Americans’ reported nights of insufficient sleep more than double as nighttime temperatures rise during summer months, an analysis of federal health data and weather records concludes.

And people will have even more trouble getting rest in years to come due to climate change, predicts study lead author Nick Obradovich. He’s a postdoctoral fellow with Harvard University’s Kennedy School of Government.

“Climate change is likely to increase the frequency of unusually warm nighttime temperatures,” Obradovich said. “If you look at the climate model output for temperatures in 2050 and 2099, we project there will be an increase in insufficient sleep as a result of that increase in temperature going forward.”

Americans will experience 9 million more nights of poor sleep in a month in which nightly temperatures average 1.8 degrees Fahrenheit higher than normal. Annually, that’s 110 million extra nights of insufficient sleep, the researchers say.

Obradovich and his colleagues gathered data on Americans’ sleep quality from an ongoing survey conducted by the U.S. Centers for Disease Control and Prevention. One question asks how many days during the previous month participants did not get enough sleep.

The researchers then gathered weather data for the city in which each survey participant lived, and compared nighttime temperatures to reports of sleeplessness.

The investigators found that hot weather is hardest on low-income people and seniors:

People making less than $50,000 annually reported nearly three times as much insufficient sleep on warmer-than-average nights, compared with those of greater means.
Adults 65 or older had twice the number of sleepless nights during hot weather as younger adults.
Low-income elderly fared the worst, with 10 times as many sleepless nights as everyone else.
“The hottest times of the year and in the most vulnerable populations are where we see the largest effects,” Obradovich said. People with little money either live in places without air conditioning or can’t afford to run their AC all the time, he noted.

Meanwhile, seniors are not as able to regulate their body temperature as well as younger people can, making them more vulnerable to heat, Obradovich pointed out.

Sleep expert Dr. Douglas Kirsch said the study proposes a “reasonable supposition.” He is medical director of Carolinas HealthCare Sleep Medicine in Charlotte, N.C., and was not involved with the research.

“We know if it’s really hot, you don’t sleep well,” said Kirsch. “The body tends to prefer to be cool to sleep well. People who have sleep disorders in particular are much more prone to need cooler temperatures in order to sleep well.”

At the same time, the projections of sleeplessness due to climate change should be taken with a grain of salt, said Kirsch, who is also a member of the American Academy of Sleep Medicine’s board of directors.

The study authors “make a whole bunch of projections about how they believe if everything maps in linear fashion, as climate change worsens then sleep must get worse,” Kirsch said. “I think that may be a little bit harder of an argument to make. It makes a number of assumptions.”

However, Obradovich and Kirsch agreed that poor sleep can have a huge impact on your quality of life and ability to work.

Kirsch said good sleep helps maintain your ability to concentrate, pay attention and maintain a stable mood.

“All those things become poorly regulated when you don’t get sufficient sleep,” Kirsch said. “Insufficient sleep is likely to lead to people not performing at their best.”

And Obradovich suggested, more frequent hot nights also could lead to an increase in deaths among the elderly, who need sleep to allow them to recover from heat stress.

These data are based on the United States, he said, one of the wealthiest countries in the world and a nation blessed with relatively temperate weather.

“If we had such data from India or Brazil, we might expect the effects would be larger in those countries,” Obradovich said.

The study was published May 26 in the journal Science Advances.