London, May 22 Increasing ambient temperatures, caused by human-induced climate change, can negatively impact how humans sleep around the globe, finds a study.
The study, published in the journal One Earth, suggests that by the year 2099, suboptimal temperatures may erode 50 to 58 hours of sleep per person per year.
In addition, it 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," said first author Kelton Minor from the University of Copenhagen in Denmark.
"In order to make informed climate policy decisions moving forward, we need to better account for the full spectrum of plausible future climate impacts extending from today's societal greenhouse gas emissions choices," Minor added.
It's long been known that hot days increase deaths and hospitalisations and worsen human performance, yet the biological and behavioural mechanisms underlying these impacts have not been well understood.
The study provides the first planetary-scale evidence that warmer-than-average temperatures eroded human sleep, "primarily by delaying when people fall asleep and by advancing when they wake up during hot weather", Minor said.
For the study, the team used sleep data collected from 7 million nightly sleep records from more than 47,000 adults wearing accelerometer-based sleep-tracking wristbands, across 68 countries spanning all continents except for Antarctica.
The study suggested that on very warm nights (greater than 30 degrees Celsius), sleep declines an average of just over 14 minutes. The likelihood of getting less than seven hours of sleep also increases as temperatures rise.
"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."
He added that in order for our bodies to transfer heat, the surrounding environment needs to be cooler than we are.
The team also found that under normal living routines, people appear far better at adapting to colder outside temperatures than hotter conditions.
"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.
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