Rising nighttime temperatures may be disturbing our sleep, a new study of self-recorded sleep loss reveals. | Carla Schaffer/ AAAS
Warmer-than-normal nights are disturbing sleep, particularly during the summer and among elderly and lower-income individuals, according to research published in the 26 May issue of Science Advances.
The investigation of self-reported sleep patterns and nighttime temperatures across the United States is one of the first studies to provide evidence that rising temperatures, driven by climate change, could affect human sleep.
Study authors Nick Obradovich, a postdoctoral fellow at Harvard Kennedy School, and Robyn Migliorini, a Ph.D. candidate in San Diego State University and University of California's clinical psychology doctoral program, came up with the idea for the study during an abnormally warm October in San Diego nearly two years ago.
"Our friends and colleagues in grad school weren't sleeping well at night — sheets off, tossing and turning in the heat — and as a result people were lethargic and somewhat grumpy," Obradovich said.
"I wondered if anyone had linked what sleep researchers know from lab studies of temperature and sleep quality to observations outside of the lab, and ultimately to climate change."
The team of researchers began investigating responses to a set of Centers for Disease Control surveys about health-related risk behaviors, including sleep patterns. Coincidentally, Migliorini was randomly selected to be interviewed for the next annual survey while conducting this research. Being a study participant helped her gain insight into what the survey experience was like, she said.
The researchers studied these CDC reports of inadequate sleep levels from 765,000 individuals across the country alongside city-level nighttime temperature data from 2002 to 2011.
Reports of disturbed sleep more than doubled during the summers, compared to other seasons, and individuals making less than $50,000 a year reported nearly three times the amount of insufficient sleep during nights that were 1.8° Fahrenheit or higher above normal temperature.
Obradovich said that more reports of poor sleep among lower-income people are probably driven by financial factors that affect their sleeping environments. A tighter budget makes it more difficult to run air conditioning all night, for example, he said. "And as we saw in San Diego, it's the cheaper apartments that don't have any air conditioning at all."
People over the age of 65 reported almost twice the amount of disturbed sleep during warm nights — a finding related to older people lacking the ability to regulate their body temperatures as well as younger people, Obradovich explained.
The researchers also studied how climate change may worsen sleep loss.
Overall, the results showed if nighttime temperature increased 1.8 °Fahrenheit above normal across the United States for a month, people would report 9 million more nights of insufficient sleep during that period.
"I am most concerned by the fact that a substantial portion of American adults already report sleep difficulties and that increases in nighttime warming could further exacerbate the problem," Migliorini said.
Inadequate sleep has been found to make people more vulnerable to psychological and cognitive functioning deficiencies, she said, and can negatively impact our immune systems. "As insufficient sleep becomes more frequent, the risk of potential health impacts rises," she added.
Obradovich cautioned that future predictions of insufficient sleep are estimates, not certainties.
"One thing that is pretty clear, though, is that human sleep is affected by nighttime temperatures," he said. "In order to sleep well during the summer when temperatures are warmer than normal, we may need to adapt by using more air conditioning, added fans at night and other technologies to counteract altered future temperatures."
Obradovich observed that since the study data was gathered in the United States, a primarily temperate nation and among the world's wealthiest, we might see that other hotter, poorer countries report even more sleep loss.
[Credit for associated image: Peopleimages/istockphoto]