Cutting sleep short on a regular basis may harm immune stem cells, potentially increasing the risk of inflammatory disorders and heart disease, a small new study suggests.
An analysis of blood samples from 14 healthy volunteers who agreed to have their sleep shortened by 1½ hours each night for six weeks revealed long-term changes in the way these stem cells behaved, leading to a proliferation of the white blood cells that can spark inflammation, according to the report published Wednesday in the Journal of Experimental Medicine.
“The key message from this study is that sleep lessens inflammation and loss of sleep increases inflammation,” said study co-author Filip Swirski, the director of the Cardiovascular Research Institute at Icahn Mount Sinai in New York. “In subjects who had undergone sleep restriction, the number of immune cells circulating in the blood was higher. These cells are key players in inflammation.”
While a certain amount of inflammation is needed to fight infections and to heal wounds, too much can be harmful, he explained. Overabundant, persistent inflammation has been linked to heart disease and neurodegenerative diseases, like Alzheimer’s, he added.
To look at the impact of restricted sleep on the immune system, Swirski and his colleagues conducted experiments in humans and in mice.
For the human study, the researchers recruited volunteers — seven men and seven women with an average age of 35 — who normally slept eight hours a night.
In the first part of that experiment, the volunteers were monitored sleeping as they typically did for six weeks, after which, the researchers drew blood samples and analyzed their immune cell content. For the next phase, the volunteers’ sleep was cut by 90 minutes each night for six weeks. Once again, the researchers drew blood samples and totaled the number of immune cells.
When Swirski and his colleagues compared the data from the two sets of blood samples, they found an increase in the number of immune cells after the six weeks of sleep restriction. An earlier animal study had revealed an increase in inflammation when the number of immune cells rose.
Moreover, the stem cells that give birth to immune cells had changed as a result of the six weeks of shortened sleep. While their basic DNA coding remained the same, the programming that controls which bits of genetic material would be turned on and off —a process known as epigenetics — was altered.
Although the numbers of immune cells may return to normal weeks later, there appears to be a more permanent mark on the stem cells. Like scars on the body that can grow larger with repeated injuries, the marks can be extended if there are more bouts of restricted sleep, Swirski said.
Those marks on the stem cells, through a series of steps, eventually lead to less diversity among the immune cells. Less diversity means that some jobs might not be done while others are being overdone, Swirski explained. So, the immune system works less well, somewhat in the way that constructing a house wouldn’t be as successful if the building crew had carpenters, but no plumbers.
How the lack of sleep affects how we age
The changes the Mount Sinai researchers saw in the experiments mirror what happens as humans age.
“As a natural consequence of aging, we lose diversity,” Swirski said. “By interrupting sleep, we are speeding up the process of aging.”
“The real key is there are things we can do through lifestyle — getting enough sleep, managing stress, getting enough exercise, consuming a healthy diet — that can reduce the speed of biological aging,” Swirski said. “We may not live forever, but we may live well into old age maintaining the quality of our lives by paying attention to some of these lifestyle factors.”
While it was known from clinical observations that chronic lack of sleep could weaken the immune system, the new study provides a mechanism to explain how it happens, said Dr. Stephen Chan, director of the Vascular Medicine Institute at the University of Pittsburgh School of Medicine.
This shows that you can’t run yourself ragged during the week and make up for it on the weekend.
— Kristen Knutson, Northwestern Feinberg School of Medicine
“We fundamentally did not understand why at the cellular level, sleep was so important in the control of the immune system," he said. "It’s really important to understand how sleep might impact inflammatory diseases like sepsis, cardiovascular disease, Alzheimer’s and dementia.”
Scientists have hoped that it was possible to catch up on poor sleep and get back to normal.
“It’s turning out that that is not true," Chan said. "We knew there was a connection between sleep and the development of dementia years later. This could be the explanation.”
He hopes there will be more studies that look at whether the impact of poor sleep habits are permanent.
“This study deserves a lot of follow-up into how durable the effects are," Chan said. "Will they linger for years, or decades or only months?”
The new study is “elegant,” said Kristen Knutson, an associate professor at the Center for Circadian and Sleep Medicine at the Northwestern Feinberg School of Medicine.
“They emphasized the long-term effects of sleep impairment that we don’t quickly recover from and they showed this in both animal and human studies,” she said. “This shows that you can’t run yourself ragged during the week and make up for it on the weekend.”
When you say immune system, people just think about infectious diseases, Knutson said.
“But it plays a big role in a lot of other health conditions,” she added. “Anything that impairs the immune system can have far-ranging effects.”