Ambient Temperature and Sleep
Dr. Obradovich’s 2017 study, which the authors call an “inaugural” investigation into the relationship among climatic anomalies, insufficient sleep, and projected climate change, also used data from 765,000 respondents to a question on the CDC Behavioral Risk Factor Surveillance Survey that asked on how many of the previous 30 days they had felt they did not get enough rest or sleep (Sci Adv. 2017;3:e1601555). Responses to the question were gathered between 2002 and 2011.
Explore This IssueMarch 2021
Each respondent’s answer was documented by interview data and geolocated to the city level, and then coupled with nighttime temperature data taken from the National Centers for Environmental Information Global Historical Climatology Network Daily, which provides station-level daily temperature and precipitation information, as well as climate normals data. The study found a robust link between insufficient sleep and atypical nighttime temperatures. “As normal nighttime temperatures increased, so too did reports of poor quality or worse sleep,” said Dr. Obradovich.
When looking at subgroups of respondents, Dr. Obradovich and his colleagues also found that the largest impact of atypical nighttime temperatures occurred during the summer and among vulnerable populations, including the elderly and people in low-income groups. “The group of low-income elderly had the highest effect size by a substantial margin in terms of the relationship between nighttime temperature and poor-quality sleep,” Dr. Obradovich added.
As normal nighttime temperatures increased, so too did reports of poor quality or worse sleep. —Nick Obradovich, PhD
One clear limitation of the study, acknowledged Dr. Obradovich, is its reliance on self-reported sleep quality. To overcome that issue, he and his colleagues published another study in 2020 in which they compiled more objective sleep measurement data from wearable devices that record nighttime sleep to assess the impact of ambient heat. Between 2015 and 2017, sleep measurements drawn from 7 million nighttime sleep records compiled from these devices worn by people in 68 countries were linked to local daily meteorological data.
Currently published online prior to publication, this study, led by Kelton Minor, PD, Copenhagen Center for Social Data Science, University of Copenhagen, found that rising nighttime temperatures were associated with shortened sleep duration mainly by delaying the onset of sleep. Residents of lower-income countries, older adults, and females were substantially more affected by sleep loss due to temperature.
Using climate model projections in both studies, Dr. Minor and colleagues assessed the potential impacts of future climate changes on human sleep and found it likely that climate change will continue to increase the frequency of warmer nighttime temperature, which, in turn, will further erode human sleep.
The public health risks of populations of people experiencing insufficient sleep are potentially enormous, Dr. Minor and his colleagues suggest, citing data linking insufficient sleep to an increased risk of negative behavioral, social, and economic outcomes. Noting the potential for sleep to mitigate these negative outcomes, they state in their article that “addressing the nocturnal impact of rising ambient temperatures on human sleep may be an efficient early intervention to reduce downstream adverse behavioral impacts linked to insufficient sleep.”