Sleep research has evolved enormously in recent decades and has revealed the far-reaching importance of sleep for virtually every system in the body. As research has continued to explore the links between sleep and physical health, it has become increasingly clear that sleep and the immune system are closely linked.

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The immune system is critical to overall health. It is essential for healing wounds, fighting off infections and protecting against chronic and life-threatening diseases.

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Sleep and the immune system are interrelated. Immune reactions, such as those triggered by a viral infection, can impair sleep. At the same time, regular sleep strengthens the immune system and enables balanced and effective immune function.

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Lack of sleep, on the other hand, can throw the immune system out of balance. There is evidence that lack of sleep can make you ill both in the short and long term.

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How does the immune system work?

The immune system is a complex network throughout the body that provides multiple defense mechanisms against disease. These defenses are generally divided into two major categories: innate and adaptive immunity. Innate immunity is broad-based protection with multiple layers of defense. Adaptive immunity, also known as acquired immunity, comprises defenses that develop over time and are focused on specific threats.

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An overview of the immune system

Numerous components contribute to the complexity of the immune system. Leukocytes or white blood cells are an important part of our immune system. The task of leukocytes is to recognize, attack and remove foreign pathogens from our body. Our immune system reacts to pathogens in immediate (innate) and learned (adaptive) ways, which enables us to safely interact with our environment every day.

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When a white blood cell detects a foreign pathogen, it releases cytokines to tell other white blood cells to prepare to attack. Cytokines are proteins that function as messengers for the immune system. Other chemicals, such as histamine, are also involved in immune reactions such as swelling or redness.

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Balanced immune response

When the immune system is functioning optimally, it maintains a delicate balance. When a threat or injury occurs, the immune system triggers reactions such as redness, inflammation (swelling), fatigue, fever, and/or pain.

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It is important that the immune system is strong enough to detect and combat potential threats, but it must also be well regulated so that the body is not constantly on alert or in attack mode.

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How does sleep affect the immune system?

Sleep is an important support for the immune system. A sufficient number of hours of high-quality sleep enables a balanced immune defense, which is characterized by strong innate and adaptive immunity.

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In contrast, serious sleep problems, including sleep disorders such as insomnia, sleep apnea, and circadian rhythm disorders, can interfere with the healthy functioning of the immune system.

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Sleep and innate and adaptive immunity

Sleep is an important phase of physical recovery and regeneration. Studies suggest that sleep plays a crucial role in the resilience of our immune system. In fact, sleep contributes to both innate and adaptive immunity.

Researchers have discovered that certain components of the immune system get up and running during a night's sleep. For example, there is an increase in the production of cytokines associated with inflammation. This activity appears to be controlled both by sleep and by the circadian rhythm, i.e. the body's 24-hour clock.

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When we're sick or injured, this inflammatory response can help recovery by boosting innate and adaptive immunity as the body works to heal wounds or fight off an infection.

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However, studies have found that this inflammation occurs even when a person is not actively injured or ill. Analysis of the types of cells and cytokines involved in this nocturnal immune activity suggests that it helps strengthen adaptive immunity.

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Just as sleep can help the brain consolidate learning and memory, research suggests that sleep boosts immune memory. The interplay of immune system components during sleep strengthens the immune system's ability to remember how to recognize and respond to dangerous antigens.

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Experts aren't sure why this process occurs during sleep, but it's suggested that there may be several factors involved:

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- During sleep, breathing and muscle activity slow down so that the immune system has energy available for these important tasks.

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- The inflammations that take place during sleep could impair physical and mental performance if they occurred while awake, which is why the body has developed to carry out these processes during sleep at night.

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- Melatonin, a sleep-promoting hormone that is produced at night, is able to counteract the stress that can result from inflammation during sleep.

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While this immune system activity during sleep is beneficial, an important aspect of this process is that it regulates itself. When the sleep period comes to an end, the body's circadian rhythm slows down this inflammation. In this way, adequate, high-quality sleep promotes the delicate balance of immune function, which is crucial for both innate and adaptive immunity.

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Can sleep deprivation make you sick?

Sleep deprivation has far-reaching effects on health and there is growing evidence that it can disrupt the immune system and increase the risk of becoming ill.

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Lack of sleep at night is associated with both short-term illnesses and the risk of chronic diseases such as diabetes and heart problems. Researchers increasingly believe that this is linked to the fact that lack of sleep impairs the normal function of the immune system.

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In the short term, the risk of infections is higher among people who sleep less than six or seven hours a night. Studies have found that inadequate sleep increases the likelihood of catching a cold or flu. In addition, lack of sleep can hinder people's recovery in intensive care units.

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Lack of sleep is linked to numerous long-term health problems, and this is thought to be linked to the negative effects of lack of sleep on the immune system. In people with healthy sleep, nocturnal inflammation returns to normal levels before waking up. However, in people who get too little sleep, this normally self-regulating system fails and the inflammation persists.

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This low level of systemic inflammation takes its toll and contributes to an increased risk of diabetes, cardiovascular disease, pain, and neurodegenerative diseases. Persistent inflammation has been linked to depression, which may explain the high rate of this disorder among people with sleep problems. Inflammation is also linked to cancer, which, according to animal studies, can be made worse by inadequate sleep.

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Unfortunately, some people manage to get through the day with little sleep, but studies suggest that the immune system doesn't learn to “get used to” lack of sleep. Instead, this mild inflammation can become chronic and further worsen long-term health.

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How the immune system affects sleep

Although sleep plays a crucial role in immune function, the immune system also influences sleep in a variety of ways.

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Infections can trigger various immune system responses, including lack of energy and drowsiness. This is one of the reasons why sick people often spend more time in bed and sleeping.

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The type of sleep also changes during an infection, so that the time spent in certain sleep phases is altered. In particular, the immune response causes more time to be spent in stage 3 of non-rapid eye movement (NREM) sleep, also known as deep sleep. During deep sleep, body processes slow down more, so that the immune system can spend more energy fighting infection.

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Fever is another important immune response. A higher body temperature can trigger new waves of immune defense and also makes the body more hostile to many pathogens. Some experts believe that the sleep changes triggered by an infection serve to ease fever and the body's fight against foreign pathogens.

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In addition, shivering is beneficial for releasing heat and maintaining fever. During REM sleep, our bodies cannot shiver due to muscle atony, and therefore REM sleep is virtually suspended during an active infection. The fragmentation of REM sleep during fever has led to so-called “fever dreams,” or increased nightmares during fever.

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As researchers continue to study the relationships between sleep and the immune system, these effects show how closely they are linked and how the immune system can use sleep to improve its ability to fight infection.

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How can we improve sleep and boost immunity?

Given the importance of sleep for immune function, taking care to get an adequate amount of uninterrupted sleep each night can help strengthen the immune system.

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Improving sleep often starts with focusing on your habits, routines, and sleeping environment, and even whether you have the best mattress for your needs. Even simple measures such as a fixed sleep schedule and avoiding mobile phones and tablets in bed can help us sleep better at night.

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People with chronic or severe sleep problems or problems with recurring illnesses should talk to a doctor. A doctor can find out the underlying cause and take the best steps to address it.

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People with sleep disorders, such as insomnia, may benefit from treatment such as cognitive behavioral therapy for insomnia (CBT-I). This approach aims to reduce negative thoughts about sleep and promotes healthy sleep and the reduction of signs of inflammation.

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Relaxation techniques, including body-oriented methods such as yoga or tai chi, have also shown positive results in improving sleep while improving immune system function, including reducing indicators of systemic inflammation.