Years of robust research have shown the importance of sleep to human health. Studies spanning several decades document the profound impact of poor quality and insufficient sleep on an array of health issues, including hypertension, obesity, type 2 diabetes, cardiovascular disease, neurodegeneration and dementia, and impaired immune functioning.
Explore This IssueMarch 2021
But sleep wasn’t always considered critical to health; only with an evolving deeper physiological understanding of the science of sleep and circadian rhythms did sleep emerge as a component of health that warranted its own subspecialty. In 2003, sleep medicine was recognized by the Accreditation Council for Graduate Medical Education, and in 2005 the Journal of Clinical Sleep Medicine was established by the American Academy of Sleep Medicine, which itself has only been around since 1975.
Climate change too has evolved over time as its effects on ecosystems, including human health, have become ever more apparent. Here too, robust research is increasingly showing the ill effects of environmental changes, from rising temperatures to severe weather events, on human health—so much so that two of the most prominent medical journals have established content devoted to the intersection of climate change and health:
- In 2016, The Lancet launched the “Lancet Countdown: Tracking Progress and Climate Change.” Among other resources, the Countdown publishes an annual report describing key areas of health and climate change.
- In 2019, the New England Journal of Medicine launched “Climate Crisis and Health” to provide articles and resources on the effects of climate change on physical and psychological health.
It isn’t surprising, then, that some investigators are now bringing these two robust avenues of research together to examine how climate change affects sleep.
Finding the Connection
Nick Obradovich, PhD, senior research scientist and principal investigator at the Max Planck Institute for Human Development in the Center for Humans and Machines in Berlin, is one of the first researchers to investigate the connection between sleep and ambient temperature. In 2017, he and his colleagues published the first evidence showing that climate change may disrupt human sleep (Sci Adv. 2017;3:e1601555).
Dr. Obradovich initiated the study of the effects of nighttime temperature on sleep when he noticed that he and his friends were experiencing disrupted sleep during a heat wave in San Diego in October 2015. He realized he had access to a data set by which he could study the social impact of climate change on sleep.
“At the time, I assumed there would be extensive literature on sleep quality and ambient temperatures, but there really wasn’t any,” he said. “I was surprised then and am more surprised now at the lack of attention to this topic because even in the absence of climate change, understanding environmental determinants of sleep quality is a really big deal.”
Daniel I. Rifkin, MD, PhD, founder and medical director of Sleep Medicine Centers of Western New York and a clinical assistant professor of neurology at the State University of New York at Buffalo, credited Dr. Obradovich’s research with igniting his own interest in looking more closely at the effect of climate change on sleep.
“The field of sleep medicine needed a study that compiled all the studies [on climate change and sleep] to help us understand how we study this further,” he said. “We’ve learned a lot about all the effects of climate change such as rising temperatures, more extreme weather events, and their downstream effects like ticks moving further north, waterborne illness, and people displaced from their homes, but we really don’t understand fully just yet how that will affect sleep.”
To gain a better answer, he and his colleagues undertook a systematic literature review of the available data and published their findings in Sleep Medicine Review (Sleep Med Rev. 2018;42:3-9).
The literature review looked at empirical studies published between 1980 and 2017 that examined the association between climate change and any aspect of human sleep. Of the 1,719 studies identified, only 16 studies met inclusion criteria. Studies excluded from analysis included non-human studies, laboratory or experimental physiological studies, articles on wind turbines, review articles, and commentaries or letters. The final 16 included studies that examined temperature and sleep (6), extreme weather events and sleep (7), and floods, wildfires, and sleep (3).
According to Dr. Rifkin, enough evidence from these studies clearly showed that climate change affects total sleep times and can lead to insomnia. “This was shown over and over in our study and was more prominent in vulnerable populations like the elderly and the socioeconomically disadvantaged,” he said.
Highlighted in the study were the specific effects of temperature and weather events on total sleep time, which diminished due to sleep disruption, rather than self-induced insufficient sleep or new-onset sleep disorders. Difficulty with sleep maintenance was also widely seen, in contrast to difficulty with sleep onset.
A big takeaway from the review, however, is that there are significant gaps in the literature regarding links between sleep and climate change due to particular types of events (e.g., drought); differential effects on sleep when power is lost during extreme heat events, for example; and the effect of climate change on sleep health services.
“The studies themselves weren’t that robust,” said Dr. Rifkin, citing Dr. Obradovich’s study as the outlier and one of the most robust studies to date.
To help broaden and deepen an understanding of the effects of climate change on sleep, Dr. Rifkin and his colleagues developed a conceptual framework for guiding future research based on identifying emerging climate change threats and their effects on sleep (see below). Based on some of the findings of their literature review, the schematic highlights the need for more research to establish a clear association between the effects of climate change and sleep.