Reduced sleep quality affects human mental health and cognitive functioning.
Some retrospective, self-report studies suggest that sleep quality reduces during warm weather. However, they may lack reliability due to their basis on memory instead of objective measures.
As a result, whether outside temperatures affect sleep quality remains unknown.
Recently, researchers analyzed a global sample of sleep data from sleep-tracking wristbands.
They found that increased outdoor temperatures are linked to lower sleep duration.
“Studies from multiple disciplines have repeatedly shown that poor sleep is implicated in a range of negative health outcomes, from reduced immune function to worsened cardiovascular outcomes to poorer mental health,” said Marshall Burke, Ph.D., Associate Professor of Earth System Science at Stanford University, who’s not involved in the study.
“Poor sleep also erodes performance at work and at school. The fact that temperature effects are so widespread and that hot nighttime temperatures will become increasingly common in coming decades, make these findings very important,” Prof. Burke told Medical News Today.
The study was published in One Earth.
Sleep quality and temperatures
The researchers examined 10 billion sleep observations for their study, comprising over 7 million repeated daily sleep records from 47,628 adults across 68 countries on every continent, excluding Antarctica. These observations included nighttime sleep duration and sleep timing: sleep onset, midsleep, and offset.
The researchers then compared this data with geolocated meteorological and climate data.
They found that increases in nighttime temperature reduce sleep duration regardless of location and that effects intensify as temperature increases.
They noted that the probability of sleeping less than 7 hours increases gradually up to 10°C, and when the temperatures exceed 10°C, the chance of reduced sleep increases at an elevated rate.
Nighttime temperatures higher than 25°C were linked to 14 minutes less sleep than those sleeping at temperatures below 10°C.
Certain demographics were more affected than others. A one degree Celcius increase in minimum temperature affected the elderly twice as much as other groups.
Those living in poorer countries were almost three times more affected than those in wealthier countries, and women were significantly more affected than men.
They further found that people do not adapt to sleeping in warmer temperatures meaning that sleep quality is generally poorer in warmer climates than in cooler ones.