The links between proper sleep and a properly functioning immune system have been obvious for medically-inclined people for thousands of years.
Back in 350 BC, Aristotle noted a sleep response in feverish patients.
The relationship between sleep and the immune system is bidirectional. One affects the other and vice-versa.
It is relatively easy to demonstrate the impact of an immune challenge on sleep. Some patients respond to infectious diseases with copious amounts of sleep. It is somewhat trickier to demonstrate causality in the other direction.
The link does, however, exist and science has long proven it. That is what we discuss in this article.
- Immunity during nocturnal sleep. Circadian factors versus nocturnal sleep.
- Sleep disturbance and the risk of infectious disease. Changes in the immune system.
- The inflammatory regulation of sleep.
- Sleep and viral infections.
Immunity and Proper Sleep
Science has known about the homeostatic effect of nocturnal sleep on the immune system for quite some time.
What is a homeostatic state? It is a state of relative equilibrium, in which the body can exist without discomfort. Whenever it deals with a viral or bacterial infection, it makes efforts to restore this state.
Scientific experience shows that nocturnal sleep has a regulatory effect on immunity. This effect is separate from the immune-regulatory effect of the circadian system.
Several scientific studies have looked at the immune responses of test subjects deprived of sleep. They then compared these responses to those of test subjects getting a normal amount of nocturnal sleep.
The conclusions were interesting.
Circadian factors regulate the distribution of immune cells. More precisely:
- Due to this circadian influence, the amount of immune cells reaches a maximum concentration towards the evening. This happens regardless of nocturnal sleep.
- Immune cell concentrations gradually drop during the night, reaching a low in the morning.
This variation in concentration correlates with the presence of cortisol. It is, again, independent of nocturnal sleep. This is one aspect of the immune system that nocturnal sleep does not impact.
Adaptive immune responses are a different story. They make up the part of the immune system that nocturnal sleep directly impacts.
Researchers have identified a wide selection of immune cells, that are part of the adaptive immune system.
The adaptive immune system is the acquired immune system. As such, it is comprised of highly specialized immune cells.
Innate immunity is yet another immune subsystem that responds to nocturnal sleep. Innate immunity is the non-specific, general immune system of your body, which is the first to act when it detects a bacterial or viral intrusion. NK (Natural Killer) cell activity relies heavily on sleep.
- NK cell counts register a minimum during the early part of the night.
- As the night wears on, more and more NK cells appear, to reach a peak in the early morning hours.
In people with sleep disturbance, this early morning peak becomes flattened. Thus, they get less NK protection in the morning than those who sleep well. Circadian factors make sure, however, that the NK cell supply does not dry up.
Sleep Disturbance and Infectious Diseases
As mentioned, sleep is a primary modulator of the adaptive immune system. This subset of the immune system is the one responsible for fending off infectious diseases. This makes the link between sleep and infectious diseases obvious.
The weakening of the adaptive immune system is most pronounced after missing a single night of sleep or as a response to naturally occurring fragmented sleep. The mechanism of the immune system weakening is extremely intricate.
A simplistic explanation would be that the body suppresses antiviral immune response genes and boosts inflammatory response genes.
Experimental sleep deprivation produces significant changes in the adaptive immune system after a single night of sleep deprivation.
The same goes for naturalistic sleep disturbance.
The link between infectious diseases and the immune system becomes clear in the context of responses to vaccines.
In a 2002 study, Spiegel K, Sheridan JF, and Van Cauter E have noticed that immunologic responses to influenza A vaccinations were reduced by as much as 50% in sleep-deprived people. The baseline for the study was a group of people who maintained proper sleep schedules. This study used experimental sleep deprivation.
Naturalistic sleep deprivation produced similar results concerning vaccination responses.
A 2012 study, by Prather AA, Hall M, and others, drew another link between sleep and vaccination responses. According to this experiment, sleep duration is strongly linked to reduced levels of protection by the hepatitis B vaccine.
The study used a relatively large sample of 125 adults.
Despite this data, we cannot say that we know all the mechanisms by which sleep impacts the adaptive immune system.
Researchers have postulated that sleep might re-allocate energy used for various wakeful processes. The body then puts this extra energy toward strengthening immune responses to infectious diseases.
Hormonal processes taking place during sleep also have “a hand” in improving immune responses.
Growth hormone and prolactin are hormones that promote immunological memory. The body releases both hormones early in the night, during the early stages of sleep.
The Inflammatory Regulation of Sleep
Just as sleep influences the immune system, so do various immunological challenges impact sleep. The links between sleep and the immune system are bidirectional.
Scientists have associated many infectious diseases with sleep disorders. In this respect, the process of eliciting a sleep disorder can be of two types.
- The pathogen triggers sleep disorder through direct action.
- The pathogen triggers an immune response, which then leads to a sleep disorder.
Most infectious diseases trigger an alteration of sleep patterns. This alteration usually happens during the acute stage of the immune response. How exactly does infection alter sleep?
- Infectious processes tend to prolong slow-wave sleep.
- Thus, they shorten REM sleep and wakefulness.
In a word: sickness makes you sleep more and dream less. This type of response is almost certainly a mechanism through which the body aims to deal with the viral/bacterial intrusion more effectively. It can accomplish that objective by preserving and redirecting energy.
Sleep and Viral Infections
Most viral infections trigger sleep disorders. Most of these disorders involve the suppression of REM sleep and the prolonging of non-REM sleep. Interestingly, not all viruses trigger such sleep-schedule changes.
Only certain strains of influenza viruses cause such changes, for instance.
- Lethargic encephalitis triggers hypersomnolence (excessive sleepiness).
- Poliovirus may lead to sleep disturbances several years after infection. It may even trigger Obstructive Sleep Apnea, as well as restless leg syndrome.
- HIV causes fatigue and various sleep disorders, even in its asymptomatic stage.
- Varicella-zoster is another virus that triggers fatigue and sleep disorders.
- Hepatitis C and B infection may decrease the amplitude of delta waves during slow-wave sleep. This often causes hypothermia.
Sleep disturbance-related responses to viral infection may also differ, depending on the stage of infection.
In a 2000 study, Drake CL, Royer H, and others, infected participants with type 23 rhinovirus. The infection decreased sleep time. Sleep efficiency fell by 5% during the active stage of the infection. During the incubation period, the researchers noted no such drop in sleep efficiency.
The Bottom Line
Proper sleep supports your immune system. It makes it easier for the latter to prevent and fight off infectious diseases. Sleep has an important role in the healing process as well.