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When you get sick, your sleep patterns change. That’s because the body’s immune response is closely linked to sleep regulation.
Cytokines are proteins that regulate the body’s immune response and inflammation by sending cells to infected or distressed areas. Along with regulating immune response, cytokines can also regulate sleep by interacting with neurotransmitters and hormones that directly signal key neurons in the brain.
The interplay between the immune system and sleep is complex. When we get sick–sometimes even before we know we’re ill—we need more sleep. Research shows that when the body’s immune system is amplified, production of the neurotransmitter serotonin also rises, encouraging the body to rest as it fights the infection.
Cytokines play a part in sleep regulation when you’re healthy, too, by impacting the release of neurotransmitters in the hypothalamus that regulate the sleep-wake cycle.
Because cytokines interleukin-1 beta (IL1) and tumor necrosis factor alpha (TNF) promote NREM sleep, they can shift sleep patterns in humans and animals, increasing NREM sleep. This, too, relates to the body’s immune response. In normal healthy sleep, brain temperature declines upon onset of NREM sleep and rises when the brain goes into REM. When the patient has a fever, sleep architecture changes: NREM sleep is fragmented, and REM sleep is suppressed. Less REM sleep could be evolution’s way of accommodating fever as an immune system response to infection by conserving energy.
People with the psychiatric illness or major depression tend to have both disturbed REM sleep and abnormal cytokine profiles. These links aren’t well understood, but provide more evidence of the complex relationship between sleep regulation and the immune system. Cytokines are proinflammatory, which means they increase inflammation within the body. This is thought to explain the link between cytokines and diseases such as cardiovascular disease, chronic fatigue syndrome, and autoimmune diseases.
Because sleep regulation and immune response are closely related, some hospitals are now adjusting policies to help patients get more sleep as part of an overall shift to more patient-centered care. Changes include instituting evening quiet hours and reducing unneeded nighttime interruptions so patients can get the sleep they need to heal.