“If sleep does not serve an absolutely vital function, then it is the biggest mistake the evolutionary process ever made.” – Allan Rechtschaffen.
We spend approximately one-third of our lives asleep, and yet there is still much to learn about why. Modern sleep research only began less than a century ago, when Nathaniel Kleitman founded the world’s first sleep laboratory at the University of Chicago in 1925. Since then, many of the mysteries of sleep have been uncovered by UChicago researchers, including the discovery of REM sleep by Kleitman and Eugene Aserinsky in 1953, and the characterization of the first sleep disorder, narcolepsy, by Rechtschaffen and Gerry Vogel in the early 1960’s.
But in the last two decades, the study of sleep has shifted from how it works and doesn’t work to the serious consequences when sleep is lacking. Locally, the hub of this new wave of sleep research is Eve Van Cauter, who has linked insufficient or irregular sleep to a long list of chronic diseases including diabetes, obesity, and heart disease. Earlier this week, Van Cauter was doubly honored in receiving the Frederick H. Rawson Professorship and headlining the christening of the new University of Chicago Sleep, Metabolism, and Health Center (SMAHC, pronounced “Smack”). Sleep scientists from UChicago, Northwestern University, and Harvard University gathered to discuss the latest evidence on just how important sufficient sleep is for good health. The consensus message was frightening: From infancy to the golden years, the failure to get a good night’s sleep can cause a wide variety of problems – and may be a major contributor to today’s most worrisome health trends.
The importance of sleep starts with birth, said David Gozal in his talk, and maybe even before due to epigenetic imprinting during the mother’s pregnancy. Gozal reviewed his paper from last month on the elevated risk of obesity in children with shorter and less consistent sleep patterns, but also presented even newer findings, including altered expression of metabolic genes in children who snore and mouse studies that found frequently-disrupted sleep can cause animals to ingest more food and retain more fat tissue. Meanwhile, more and more studies are finding that young children are not getting nearly as much sleep as recommended.
“Sleep curtailment is not only a problem of our adult society, but clearly has pervasively infiltrated to infants and young toddlers,” Gozal said.
The effect of poor sleep upon children may go beyond metabolic issues such as obesity and diabetes, proposed neurobiologist Daniel Margoliash. In both humans and birds, Margoliash’s laboratory has found evidence that sleep helps the brain consolidate information learned during the day into memory. As young birds sleep after a day of practicing their distinctive song, the brain recreates its activity patterns from those earlier performances, presumably part of the process of making that newly learned skill permanent. For schoolchildren, the lesson is clear: lose out on sleep, and you could be losing what you were taught during the preceding day.
Later in life, the problems associated with insufficient sleep only appear to grow worse. In older adults, chronic insomnia has been linked to cognitive decline, perturbations in hormones associated with hunger, and insulin sensitivity, said Northwestern’s Phyllis Zee. Women with polycystic ovary syndrome, a condition marked by infertility, hormonal dysregulation, obesity, and diabetes, are more than 8 times more likely to suffer from obstructive sleep apnea, said David Ehrmann. And the medical effects of poor sleep can literally appear overnight – Vineet Arora‘s study of poor sleep in noisy hospital wards found an average blood pressure increase of 6.2 mmHg for every hour of sleep lost.
All those research threads came together in Van Cauter’s lecture, where she proposed a model of interacting epidemics: obesity, diabetes, and sleep loss. While the first two health crises are often attributed to increased consumption of unhealthy food and decreased exercise, the rapid decline in sleep among all ages of Americans (from 8.5 hours in 1960 to under 7 hours today, Van Cauter said) may also play a significant role. Since the fortuitous inclusion of a glucose tolerance task in a late-1990’s sleep deprivation study, which found that people restricted to 4 hours of sleep for 6 nights showed early signs of insulin insensitivity, Van Cauter’s group has dialed in on the relationship between sleep loss and metabolic dysfunction.
With more human sleep studies, fat biopsies to look at insulin sensitivity on the cellular level, epidemiological analysis, and more, Van Cauter’s group has constructed a model of how a sleepy brain and discombobulated hormones can throw a person’s appetite far off-kilter.
“Our volunteers had a decrease in leptin that signaled an increase in hunger in the brain,” Van Cauter said. “The problem was that they were receiving the same amount of calories. The leptin levels were screaming famine in the midst of plenty.”
The good news is that poor sleep can be fixed, either through better sleep habits or treatments for sleep disorders. Some exciting preliminary data from Van Cauter’s lab looks at the effect of treating obstructive sleep apnea with CPAP on people who have both the sleep disorder and type 2 diabetes. With idealized CPAP performed in the sleep laboratory for 7 nights, researchers observed an improvement in glucose control equivalent to 6 months on commonly-used diabetes medications, Van Cauter said.
Now, with the talented, diverse array of UChicago sleep researchers united under the umbrella of SMAHC, the case for sleep’s importance can be made even more rapidly and comprehensively. With representatives from internal medicine, pediatrics, pulmonology, endocrinology, neurobiology, and anatomy, the program is poised to not only explain what humans are doing with the one-third of their lives spent in bed, but make a rich argument against the further erosion of slumber.
“There’s not going to be a magic bullet that’s going to be an effective counter-measure to the effects of sleep deprivation on any unique level. It’s going to really be a global approach,” Van Cauter said. “This type of research needs a multi-disciplinary, translational network.”