The answer to the question is not a simple yes or no. It is probably yes, but whilst there is lots of circumstantial evidence that it does, there is not much definitive evidence.
How sleep can improve your immunity | Sleeping with Science, a TED series
The importance and function of sleep and its interdependence with the immune system are not fully understood. New studies continually discover further information about the interactions between the immune system and sleep.
Research has shown that sleep is crucial for virtually every system in the body. The amount and quality of sleep a person has impacts their physical and mental health and helps to determine their vulnerability to illness. Conversely, being ill can influence how much or how little we sleep. Sleep disorders such as insomnia, sleep apnea, and circadian rhythm disruption can disrupt the immune system.
To understand how sleep might improve immunity, we should first understand sleep and how it affects the immune system. Sleep and the immune system work in a bi-directional way, with each influencing how the other works. Changes in one will lead to consequences in the other.
The immune system
The immune system can be classified into two main categories, innate or adaptive immune systems.
Innate immune reactions are generally broad-spectrum and several layers deep and can induce inflammation at the point of attack. Innate immune systems are the first line of defense against any infection, but they are non-specific.
Adaptive immune systems are acquired defenses developed over a long time in response to threats. In adaptive immune defense, white blood cells, known as leukocytes, identify and attack pathogens. They simultaneously send chemical messages via substances called cytokines to alert and attract other leukocytes. Adaptive immune systems also release histamines or instigate swelling at the site of the attack. The adaptive system must produce a balanced reaction and not overreact.
When an antigen is detected, white blood cells are sent to the area. These cells are known as B cells and T cells. B cells produce antibodies to attack the bacteria, viruses, and toxins that are invading the body. T cells kill the cells that have already been infected with viruses, cancer, etc. White blood cells can develop specific receptors which attach to specific antigens. Most white blood cells die when the infection is over, but some are retained as memory cells to combat future infections.
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Sleep and the immune system
Sleep is essential in helping to maintain balance and ensuring that any response is proportionate. Sleep disorders like insomnia, apnea, and circadian rhythm disruption can impede the immune system's effectiveness. Sleep is not a passive condition. EEG (electroencephalography ) and EOG (electrooculography) scans show that the brain and eyes are active during sleep, and there are four stages of sleep.
Stage 1 is the transition from wake to sleep and lasts a few minutes. The body slows down the heart and breathing.
Stage 2 lasts about 50% of normal sleep time. There are no eye movements, and the body temperature drops.
Stage 3 occupies 20% of normal sleep time. In this phase, the body is completely relaxed, heart rate and breathing slow, and body temperature drops slightly. Tissue repair and growth occur in this period.
Stage 4 is the phase known as REM (Rapid Eye Movement) sleep. It begins about ninety minutes after falling asleep. The heart and breathing speed up slightly, brain activity increases, and the body is temporarily paralyzed during this stage.
Sleep and the immune system are interlinked and work together. For example, when a person becomes ill, the immune system triggers a feeling of lack of energy and increases sleepiness, and sick people sleep more than usual. Sleep helps both the innate and the adaptive immune systems. During sleep, cytokine production increases, and muscle activity reduces, freeing up more energy for healing processes. The immune system produces more inflammation at night in response to infection. Inflammation could be harmful, but as sleep winds down, circadian rhythms reduce inflammation.
The immune system and the central nervous system are intricately linked, and response to infection can be physical and neural. When an infection occurs, chemical and nerve messages are triggered, which will control the immune response.
Lack of sleep has been linked to several health conditions. These include diabetes, cardiovascular disease, depression, schizophrenia, alcohol dependence, and inflammatory diseases. Poor sleep has also been associated with a higher risk of infection. It has also been linked to early mortality, although there may be other factors involved in this, and lack of sleep may be a symptom as well as a cause. There is also evidence that sleep deprivation can lead to reduced vigilance.
Studies have shown that reduced sleep before and after receiving flu vaccines can reduce the number of antibodies produced when measured up to ten days after vaccination. Studies show that good sleep increases the production of T cells after vaccination.
The function of sleep in the immune system memory is threefold.
Encoding – the body recognizes what it needs to remember.
Consolidation – the information is passed from the short term to the long term memory. In the central nervous system, data is stored in different areas of the brain. At a cellular level, this means the retention of various types of T and B cells.
Recall - activation of different T and B cells when an antigen is encountered.
A healthy adult will need about seven hours of sleep a night for the immune system to successfully complete all its functions. If sleep is too short, these memory functions are not fully completed, increasing the risk of future infection. Less than seven hours a night three days in a row is thought to be equivalent to losing one night's sleep. It is possible to catch up on sleep, but the amount of extra sleep required to catch up is difficult to determine.
Good sleep will help keep your immune system healthy but mainly as an enabler for other bodily immune functions. However, having more sleep will not necessarily improve your immunity on its own. Many different factors are involved, but what is clear is that getting a full seven or eight hours of sleep is good for your health.