Chronic sleep deprivation in a small group of healthy adults increased production of immune cells linked to inflammation while also altering the immune cells’ DNA, a new study found.
“Not only were the number of immune cells elevated, but they may be wired and programmed in a different way at the end of the six weeks of sleep restriction,” said study coauthor Cameron McAlpine, an assistant professor of cardiology and neuroscience at the Icahn School of Medicine at Mount Sinai in New York City.
“Together, these two factors could potentially predispose someone for diseases like cardiovascular disease.”
A certain amount of immune system inflammation is necessary for the body to fight infections and heal wounds, but an overactive immune system can be harmful and raise the risk of autoimmune disorders and chronic disease, experts say.
“This work aligns with views in the field that sleep restriction can increase risk for type 2 diabetes and hypertension,” said Steven Malin, an associate professor in the department of kinesiology and health at Rutgers University in New Jersey.
“Practically then, these findings support ideas to develop good sleep habits such that most of the time you are getting adequate sleep,” added Malin, who was not involved in the study.
To be healthy, the body needs to move through four stages of sleep several times each night. During the first and second stages, the body starts to decrease its rhythms. Doing so prepares us for the third stage – a deep, slow-wave sleep where the body is literally restoring itself on a cellular level – fixing damage from the day’s wear and tear and consolidating memories into long-term storage.
Rapid eye movement sleep, called REM, is the final stage in which we dream. Studies have shown that missing REM sleep may lead to memory deficit and poor cognitive outcomes as well as heart and other chronic diseases and an early death.
On the flip side, years of research has found sleep, especially the deepest, most healing kind, boosts immune functioning.
Since each sleep cycle is roughly 90 minutes long, most adults need seven to eight hours of relatively uninterrupted slumber to achieve restorative sleep, according to the US Centers for Disease Control and Prevention.
The study was small, involving 14 young, healthy people with no sleep issues. But the duration of the study was also quite long, which gave it strength, McAlpine said.
“A lot of sleep studies are one day, two days, maybe a week or two,” he said. “But there are very few that look at the influence of sleep over such a long duration of six weeks, which is what we did.”
All those in the study wore wrist accelerometers, which allowed researchers to track their sleep quality and duration over each 24-hour period. During the first six weeks, each study participant slept for the seven to eight hours that the CDC recommends for adults. For the next six weeks, they reduced their sleep by 90 minutes each night.
At the end of each six-week cycle, blood was drawn in the morning and evenings and analyzed for immune cell reactivity. No negative changes were found in people who got adequate amounts of sleep. However, after the study participants spent six weeks with sleep restriction, blood tests found an increase in a certain type of immune cell when blood was drawn in the evenings.
“This defect of the sleep restriction was very specific to one type of immune cell called a monocyte, whereas other immune cells did not respond,” McAlpine said. “This is a sign of inflammation.”
The blood tests also found epigenetic changes inside the monocyte immune cells after the long period of sleep deprivation. Epigenes are proteins and chemicals that sit like freckles on each gene, waiting to tell the gene “what to do, where to do it, and when to do it,” according to the National Human Genome Research Institute. The epigenome literally turns genes on and off, often based on environmental triggers and human behaviors such as smoking, eating an inflammatory diet or suffering a chronic lack of sleep.
“The results suggest that factors that may modify gene expression of proteins related to inflammation, known as the epi-genome, are modified by sleep restriction,” Malin said. “This modification raises risk for immune cells to be more inflammatory in nature. The study did not perform functional or clinical measures to confirm disease risk, but it does lay (the) foundation for future studies to consider these mechanisms.”
Epigenes can be turned on and off, so would the change in immune function remain after the study subjects went back to full nights of sleep? The study was unable to investigate that outcome in humans. But the researchers did additional studies in mice that produced interesting results.
Immune activity in the sleep-deprived mice mirrored that of humans – immune cell production increased, and epigenetic changes were seen in the immune cell DNA. In these studies, the mice were allowed to get 10 weeks of good sleep before being tested again.
Despite getting sufficient sleep for a long period of time, researchers found the DNA changes remained and the immune system continued its overproduction, making the mice more susceptible to inflammation and disease.
“Our findings suggest that sleep recovery is not able to fully reverse the effects of poor-quality sleep, in the mice,” McAlpine said, adding that his lab is continuing to work with people to see if that result will translate to humans. (Note: Mice studies often do not translate.)
“This study begins to identify the biological mechanisms that link sleep and immunological health over the long-term. This is important because it is yet another key observation that sleep reduces inflammation and, conversely, that sleep interruption increases inflammation,” lead author Filip Swirski, director of the Cardiovascular Research Institute at Icahn Mount Sinai, said in a statement.
“This work emphasizes the importance of adults consistently sleeping seven to eight hours a day to help prevent inflammation and disease, especially for those with underlying medical conditions.”