If global greenhouse gas emissions continue at a high level, people will get less sleep—and the elderly and those with low incomes will be hit the hardest, according to a new study in Science Advances.
According to the New York Times, research has long established that being too hot or too cold can disrupt sleep. As Sara Mednick, a sleep psychologist at the University of California at Riverside and co-author of the study, explained, "Decreasing body temperature is one of the strongest signals to our brain to bring on sleep onset." She added, "This decrease in temperature is regulated in part by the ambient temperature. Thus, when the ambient temperature is too high, the body cannot cool itself and therefore can't fall asleep."
However, prior to the latest study, no one had assessed how changing temperatures brought about by climate change might affect our overall sleep patterns, according to the study's researchers.
For the study, Nick Obradovich, a fellow at the Harvard Kennedy School and a research scientist at Massachusetts Institute of Technology's Media Lab and colleagues assessed CDC survey data from 2002 to 2011 on 765,000 Americans. Among other population health questions, CDC in the surveys asked respondents about their sleep patterns during the previous month.
Obradovich found a correlation between higher temperatures in certain cities and disrupted sleep patterns as reported by residents of those areas. Obradovich then forecast estimated levels of sleep disruption by calculating how hot various places will be if greenhouse gas emissions continue at a high level.
Based on those calculations, the researchers discovered that every nocturnal temperature increase of one degree Celsius created an additional three nights of restless sleep per 100 people per month. And assuming global emissions continue to increase at current levels, rising temperatures could add six nights of restless sleep per month for every 100 Americans by 2050, and 14 nights of restless sleep per month for every 100 Americans by 2099.
According to researchers, those hit hardest by the changes in temperature would be individuals with incomes less than $50,000 per year, as they might not be able to afford running an air conditioner through the night, and individuals over age 65, who are less able to self-regulate body temperature and are more likely to die from heat-related illnesses.
But Obradovich acknowledged that the study had several key limitations. For one, survey participants' responses about their sleep was subject to the vagaries of memory.
In addition, Obradovich pointed out that it's impossible to know what human society will look like in a century. "I don't pretend to have any high degree of confidence what sleep will look like in 2099 or 2050," he said.
Joris van Loenhout, an expert on environmental health at the Catholic University of Louvain in Belgium, praised the study. "It is an interesting and important study, which shows the relationship between warm temperatures and sleep quality, and the expected impact of climate change on this," he said.
But Jerome Siegel, the head of a sleep laboratory at the University of California, Los Angeles, said the limitations of the data and the assumptions made using that data made him hesitant. "It's sort of a nice exercise–yes, this is something that might affect people," he said. "But this would be way down on my list of things to worry about with climate change, even though I'm a sleep researcher" (Guarino, "Speaking of Science," Washington Post, 5/26; Gillis, New York Times, 5/26).
Understand the wellness spectrum
Programs aimed at promoting healthy habits among employees are likely to lead to improved employee engagement and productivity—but they're unlikely to reduce the total cost of care. To do that, you'll need to take a population health approach.