Too little sleep can harm immune cells and trigger inflammation, study says

Chronic sleep deprivation in a small group of healthy adults increased the production of immune cells linked to inflammation, as well as altering the DNA of immune cells, a new study finds.

“Not only was the number of immune cells elevated, but they can be wired and programmed differently at the end of the six weeks of sleep restriction,” said study co-author Cameron McAlpine, assistant professor of cardiology and neuroscience at Icahn. Mount Sinai School of Medicine, New York.

“Together, these two factors can predispose someone to 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 increase the risk of autoimmune disorders and chronic disease, experts say.

The findings were published September 21 in the Journal of Experimental Medicine.

“This work aligns with views in the field that sleep restriction can increase the risk of type 2 diabetes and hypertension,” said Steven Malin, 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 most of the time you get adequate sleep,” added Malin, who was not involved in the study.

a good sleep heals

To be healthy, the body needs to go through four stages of sleep several times a night. During the first and second stages, the body begins to slow down.

Doing so sets us up for stage three — deep, slow-wave sleep, where the body is literally restoring itself at a cellular level — fixing the 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 a lack of REM sleep can lead to memory deficits and poor cognitive outcomes, as well as heart disease and other chronic diseases and early death.

On the other hand, years of research have found that sleep, especially the deeper, more healing type, boosts immune functioning.

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 US Centers for Disease Control and Prevention.

Increased signs of inflammation

The study was small, involving 14 young, healthy people with no sleep problems. But the duration of the study was also quite long, which gave it strength, McAlpine said.

“Many sleep studies last a 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 study participants wore wrist accelerometers, which allowed researchers to track sleep quality and duration every 24 hours. During the first six weeks, each study participant slept for the seven to eight hours 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 collected morning and evening and analyzed for immune cell reactivity.

No negative changes were found in people who got adequate sleep. However, after study participants spent six weeks with restricted sleep, blood tests found an increase in a certain type of immune cell when blood was drawn at night.

“This sleep restriction defect was very specific to a type of immune cell called a monocyte, whereas other immune cells did not respond,” McAlpine said. “That’s a sign of inflammation.”

Blood tests also found epigenetic changes within 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 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 experiencing a chronic lack of sleep.

“The results suggest that factors that can modify the gene expression of inflammation-related proteins, known as the epigenome, are modified by sleep restriction,” Malin said.

“This modification increases the risk that immune cells are more inflammatory in nature. The study did not perform functional or clinical measures to confirm disease risk, but it lays the groundwork for future studies to consider these mechanisms.”

Epigenes can be turned on and off, so would the change in immune function remain after study participants returned to full nights sleep? The study was unable to investigate this result in humans. But the researchers did additional studies in mice that produced interesting results.

Are the changes permanent?

Immune activity in sleep-deprived mice mirrored that of humans — immune cell production increased and epigenetic changes were observed in the DNA of immune cells. In these studies, the mice got 10 weeks of good sleep before being tested again.

Despite getting enough sleep for a long period of time, the researchers found that 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 sleep in mice,” McAlpine said, adding that his lab continues to work with people to see if this result will translate in humans. (Note: mouse studies often do not translate.)

“This study begins to identify the biological mechanisms that link sleep and long-term immune health. This is important because it is yet another important observation that sleep reduces inflammation and, conversely, that sleep disruption increases inflammation,” said lead author Filip Swirski, director of the Icahn Mount Sinai Cardiovascular Research Institute, in an communicated.

“This work emphasizes the importance of adults getting consistently seven to eight hours of sleep a day to help prevent inflammation and disease, especially for those with underlying medical conditions.”