Fighting viruses with sleep

The link between sleep and the immune system was established in the 1970s in animals, and then in humans.[1] Since then, numerous studies have shown that people who are sleep-deprived are more likely to develop a cold,[2] a respiratory illness[3] or an infectious disease. Why is this? Mainly because sleep helps maintain the efficiency of your immune system’s various components.

T cells. When you are awake, these “little soldiers” are circulating in the blood to fight infections. When you sleep, they move from the bloodstream into the lymph nodes. There, “antigen-presenting” cells pass information to them about the infectious micro-organisms circulating in the body, so that they can recognize them and fend them off. In this way, T cells develop their immune memory. Without enough sleep, your lymphocytes do not have all the information to provide you with proper immunity.[4]

Integrins. To neutralize the invaders, T cells must attach themselves to the infected cells. They do this by activating integrins, proteins that you might call “adhesives.” According to one study, integrin activity was lower in sleep-deprived subjects than in subjects who were more rested, thereby affecting T cell functioning. Researchers believe that sleep promotes integrin activation by reducing stress hormones such as adrenaline.[5]

Cytokines. As soon as your immune system is activated by a pathogen, it produces cytokines, proteins that serve as communication agents between the various cells involved in the immune response. For example, it is these proteins that prompt T cells to travel to the lymph nodes (see above). Lack of sleep tends to reduce the production of cytokines, which in turn impairs the functioning of the immune system.[6]

On the other hand, a lack of sleep can sometimes trigger an overproduction of “pro-inflammatory” cytokines. Normally, these cytokines attract cells that cause inflammation to the site of the infection, helping the body defend itself against an attack. For example, raising body temperature, i.e. causing a fever, which is a form of inflammation, inhibits the reproduction of pathogens. However, sometimes the production of cytokines is excessive in relation to the infection itself and causes more harm than the infectious micro-organism. This has been seen with COVID-19, which can cause such inflammatory storms. A lack of sleep may also contribute to this excessive immune response.

Killer cells. Natural killer cells, or NK cells, are those particular white blood cells that, along with T cells, participate in killing not only infectious micro-organisms, but also cancer cells. A study carried out in the 1990s showed that just a few hours of sleep deprivation could reduce the activity of these essential warriors by almost a third.[7]

Adults who do not regularly get a good night’s sleep of seven to nine hours are more likely to get sick.

Read more: How does smartphone use effect my sleep?

By limiting the activity of the immune system, sleep deprivation can encourage the development of an infection or interfere with the quality of your immune response. Here are a few concrete examples.

One study showed that subjects who had slept an average of less than seven hours per night in the previous two weeks were nearly three times more likely to develop cold symptoms than those who had slept more than eight hours in the same period.[2]

Similar results were obtained in 2015 by Aric Prather, professor at the University of California at San Francisco, who concluded that sleeping less than six hours per night multiplies by four the risk of falling ill after being exposed to viruses.[8]

“Short sleep was more important than any other factor in predicting subjects’ likelihood of catching cold. It didn’t matter how old people were, their stress levels, their race, education or income. It didn’t matter if they were a smoker.” Aric Prather, professor at UCSF

Not getting enough sleep can reduce the effectiveness of a vaccine-induced immune response. A study conducted in 2002 showed that the number of antibodies produced following influenza vaccination was 50% lower in people who had only four hours of sleep per night during the four nights prior to vaccination than in those who had sufficient sleep.[9] These results have been confirmed repeatedly by various studies, one of which found that each additional hour of sleep was associated with an approximately 50% increase in antibodies following vaccination.[10]

Daytime drowsiness, often resulting from a lack of sleep or poor quality sleep, is also associated with a higher prevalence of fungal infections such as mycosis, as well as parasitic infections such as giardiasis and malaria. Indeed, researchers have found that the use of antiparasitic and antifungal medications was significantly higher in individuals experiencing daytime drowsiness.[11]

Read more: The impact of sleep deprivation on weight (Infographic)

By causing poor quality sleep, sleep disorders such as insomnia and sleep apnea can also affect the immune system. Numerous studies have found links between sleep disorders and the quality of the immune response.[6] According to a recent meta-analysis, sleep disorders are even more often associated with an overproduction of inflammatory cells than a sleep deficit.[12]

Although it is not a guarantee against various infections, getting enough sleep greatly reduces the risks. It also helps your system fight off pathogens more effectively and increases your immune response to vaccines. Contrary to what we have long believed, sleep supports the functioning of the entire body, not just the brain.

If you are not getting much sleep or have trouble sleeping, or if you often feel tired during the day, consider adopting lifestyle habits that are conducive to sleep. By improving the length and quality of your sleep, you are giving yourself one of the best health insurance plans available!