Hotter nights due to climate change will cost us sleep, study suggests

The impact of climate change and extreme weather events has been widely looked at regarding economic and other broad-scale health impacts. But a new study suggests it could also have a negative impact on daily human activities, such as our sleep.

The study, which looked at data from people around the world, suggests that by the year 2099, "suboptimal temperatures" may reduce sleep by 50 to 58 hours per person each year. 

Take for example, if an adult gets an average of seven hours of sleep each night, that equates to about 2,555 hours of sleeping in the year. Losing a potential 50 hours of sleep due to more extreme temperatures could shave about 2% off of total sleep time in the year.

The study also found that the temperature effect on sleep loss is substantially larger for residents from lower-income countries, as well as in older adults and females.

"Our results indicate that sleep — an essential restorative process integral for human health and productivity — may be degraded by warmer temperatures," the study’s lead author, Kelton Minor of the University of Copenhagen, said in a statement

Minor said the study was the first "planetary-scale evidence" that warmer-than-average temperatures erode human sleep.

"We show that this erosion occurs primarily by delaying when people fall asleep and by advancing when they wake up during hot weather," the study author added.

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The researchers analyzed global sleep data from sleep-tracking wristbands. This included 7 million nightly sleep records from more than 47,000 adults across 68 countries spanning all continents except for Antarctica, the study said. 

The findings suggested that on very warm nights — greater than 30 degrees Celsius, or 86 degrees Fahrenheit — sleep declines an average of just over 14 minutes. As temperatures rise, people were more likely to get less than seven hours of sleep, according to the study. 

"Our bodies are highly adapted to maintain a stable core body temperature, something that our lives depend on," Minor said. "Yet every night they do something remarkable without most of us consciously knowing — they shed heat from our core into the surrounding environment by dilating our blood vessels and increasing blood flow to our hands and feet." 

Minor added that in order for our bodies to transfer heat, the surrounding environment needs to be cooler than we are.

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FILE IMAGE - A person sleeps in a bed on Jan. 13, 2018, in his home in Brooklyn, New York. (Photo by Andrew Lichtenstein/ Corbis via Getty Images)

The study noted how people appear far better at adapting to colder outside temperatures than hotter conditions under normal living routines. 

"Across seasons, demographics, and different climate contexts, warmer outside temperatures consistently erode sleep, with the amount of sleep loss progressively increasing as temperatures become hotter," Minor said.

But one observation that stood out was among people in developing countries, who seemed to be more affected by such changes. The team theorized how a greater prevalence of air conditioning in developed countries could have played a role in the outcome, but the study didn’t have access to data on air conditioning among the participants.

"The burden of future warming will not be evenly distributed, barring further adaptation and mitigation, with people living in hotter climates expected to lose considerably more hours of sleep per year by 2099, contributing to societal impacts that scale with the level of future atmospheric (greenhouse gas) concentrations," the study concludes. "Taken together, our results demonstrate that temperature-driven sleep loss likely has and may continue to exacerbate global environmental inequalities."

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The researchers said they would like to collaborate with global climate scientists, sleep researchers and those in technology to future analyze certain populations.

The study was published on May 20 in the journal One Earth. It was funded by the Danish Agency for Higher Education and Science and the Independent Research Fund Denmark.

How much sleep does the average adult need?

The National Sleep Foundation recommends that adults between the ages of 18 to 64 get around seven to nine hours of sleep each night. Older adults, or those 65 and up, are recommended to get seven to eight hours a night. 

It also notes how sleep durations outside the recommended range "may be appropriate, but deviating far from the normal range is rare."

A Gallup survey published in 2013 found that 40% of U.S. adults were getting less than seven hours of sleep — averaging around 6.8 hours a night. That was down more than an hour from 1942.

There are a number of strategies one can implement for better sleep. This includes reducing stress before bedtime, avoiding phones and other electronic devices in the leadup to bedtime, limiting caffeine, nicotine and alcohol intake, and ensuring that the room is quiet, dark and comfortably cool. 

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This story was reported from Cincinnati.