Chronic sleep deprivation in a small group of healthy adults increased the production of immune cells linked to inflammation, while also altering the DNA of the immune cells, a new study finds.
“Not only was the number of immune cells increased, but they can be wired and programmed differently at the end of the six-week sleep restriction,” said study co-author Cameron McAlpine, an assistant professor of cardiology and neuroscience at Icahn. School of Medicine at Mount Sinai in New York City.
“Together, these two factors can predispose a person to diseases such as cardiovascular disease.”
Some degree of immune system inflammation is necessary for the body to fight infections and heal wounds, but an overactive immune system can be harmful and increase the risk of autoimmune and chronic diseases, experts say.
The study was published Sept. 21 in the Journal of Experimental Medicine.
“This work aligns with the views in the field that sleep restriction may increase the risk of 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, these findings support ideas for developing good sleep habits so that you usually get enough sleep,” added Malin, who was not involved in the study.
To be healthy, the body has to go through four sleep phases several times a night. During the first and second phases, the body begins to reduce its rhythms. When we do that, we prepare for the third stage – a deep, slow sleep in which the body literally repairs itself at a cellular level – repairing the damage of daily wear and tear and consolidating memories into long-term storage.
Sleep with rapid eye movements, called REM, is the last stage in which we dream. Studies have shown that missing REM sleep can lead to memory deficits and poor cognitive outcomes as well as heart and other chronic diseases and early death.
On the other hand, years of research have shown that sleep, especially the deepest, most healing kind, improves the immune system.
Since each sleep cycle lasts about 90 minutes, most adults need seven to eight hours of relatively uninterrupted sleep to achieve restorative sleep, according to the U.S. Centers for Disease Control and Prevention.
The study was small and included 14 young, healthy people with no sleep problems. 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 very few look at the impact of sleep over such a long six-week period, and 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. Over the next six weeks, they reduced their sleep by 90 minutes a night.
At the end of each six-week cycle, morning and evening blood was drawn and analyzed for immune cell reactivity. No negative changes were found in people who got enough sleep. However, after the study participants spent six weeks on sleep restriction, blood tests showed an increase in a certain type of immune cell when blood was drawn in the evening.
“This sleep restriction defect was highly specific for one type of immune cell, called a monocyte, while other immune cells were unresponsive,” McAlpine said. “This is a sign of inflammation.”
The blood tests also found epigenetic changes in the monocyte immune cells after the long period of sleep deprivation. Epigenes are proteins and chemicals that sit like freckles on every 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 factors and human behavior such as smoking, eating an inflammatory diet or chronic sleep deprivation.
“The results suggest that factors that can alter the gene expression of proteins associated with inflammation, known as the epi genome, are altered by sleep restriction,” Malin said. “This change increases the risk of immune cells being more inflammatory in nature. The study did not perform any 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 persist after the subjects had full nights of sleep again? The study was unable to examine that outcome in humans. But the researchers did additional studies in mice that yielded interesting results.
Immune activity in sleep-deprived mice mirrored that of humans — immune cell production increased and epigenetic changes were observed in the immune cell’s DNA. In these studies, the mice were allowed to sleep well for 10 weeks before being tested again.
Despite getting enough sleep for a long period of time, researchers found that the DNA changes persisted and the immune system continued its overproduction, making the mice more susceptible to inflammation and disease.
“Our findings suggest that sleep recovery may not completely reverse the effects of poor quality sleep. in the mice,” McAlpine said, adding that his lab continues to work with humans to see if that result will translate to humans. (Note: Studies in mice often don’t. translate.)
“This study begins to identify the biological mechanisms that link sleep and long-term immunological health. This is important because it is yet another important observation that sleep reduces inflammation and, conversely, that sleep interruption increases inflammation,” said lead author Filip Swirski, director of the Cardiovascular Research Institute at Icahn Mount Sinai, said in a statement.
“This work highlights 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.”