Sleep and the Immune System
Sleep restriction and sleep deficit increase your vulnerability to disease. The immune system is connected to the sleep regulatory system and actions of the immune system to fight off disease affect sleep architecture and duration. Sleep in both perfectly healthy people and in sick people is regulated partly by immune system components called cytokines.
Like just about everything, the immune system has a circadian rhythm. Blood counts of T-cells and levels of proinflammatory cytokines are high during the night while leukocytes and the anti-inflammatory cytokine IL-10 goes up during daytime. The immune system is both influenced by and influences sleep.
Changes in the immune system seem associated with the onset of narcolepsy, which has a neurological cause (brain cell death) Inflammatory diseases increase cytokine levels and make people feel fatigued. This is a good thing during a short-term injury or illness, as it drives the person to rest. For those with chronic inflammation, however, the immune system keeps them tired for long periods, which may explain symptoms of fibromyalgia and chronic fatigue disorder. The trouble in sleeping that people with those conditions experience is not due to just the discomforts of the illnesses, but because the sleep regulation system is affected.
Cytokines are also part of the etiology of apnea and other sleep disorders. In that sense, these disorders are partly auto-immune diseases. Scientists have investigated the use of immunology (supplementing the immune system) to treat conditions characterized by sleep disturbance, but no such treatments are available in wide use yet.
In the healthiest people, there is an interaction between the immune system and sleep regulation processes. However, it’s when someone gets sick that things get interesting and the interplay between the two systems can tell us something.
Tests in animals show that alterations in sleep behavior and architecture can by themselves serve as a prognostic indicator for bacterial and viral infection. The more pathogens the animals were given, the more the sleep was disturbed. This might sound like little comfort to people suffering with sleep disturbances when they are sick, but the action of the immune system in fighting the disease seems to alter sleep. The frequent awakenings may be irritating, but they are for your own good.
Small mammals sleep more than large ones. Small animals have higher metabolisms and produce more free radicals; in NREM sleep the body repairs free radical damage. Free radical damage can be dealt with by replacing damaged cells, but some sections of the brain do not produce new cells. NREM sleep seems to stop or slow damage although it is not clear how. Rats deprived of sleep seem to suffer brain damage.
Cytokines – biochemicals produced by the immune system – tend to suppress REM sleep, although the mechanism is not known. Interleukin-1 beta (IL1) and tumor necrosis factor alpha (TNF) promote Non-REM sleep in people both when they are healthy and sick.
When you get a vaccine, if you run short of sleep the next few days, the effectiveness of the vaccine is lowered. A new study confirms this. Sleep loss and sleep disturbance is associated with many chronic diseases including diabetes and cancer. Even a simple cold makes us want to sleep more – part of nature’s way of helping our bodies to heal.
The serotonin, or 5-hydroxytryptamine (5-HT)) system, interacts with the immune system in ways that influence sleep architecture. This gives a clue as to why depressed people (who have altered serotonin systems) usually have insomnia.
Asthma is an auto-immune disease and asthmatics often experience harsher symptoms at night. The functioning on the airways tends to be good just before sleep, and then it declines as the night goes on. This is true for everyone, but asthmatics can start wheezing during the night and their attacks wake them up.
Sleep deprivation also seems to trigger outbreak of lupus symptoms in
people who have that autoimmune disease.
The influence of short sleep on cardiovascular diseasein is unclear
Both cytokines and inflammatory markers such as C-reactive protein
increase during sleep deprivation and these could harm the heart and
circulatory system over time.
How (and why) the immune system makes us sleep
"O Sleep, rest of all things, mildest of the gods, balm of the soul..."
(Iris to Hypnos. Ovid, Metamorphoses)