A complex relationship exists between sleep and the immune system.
Many of the key biological processes associated with our immune system are intimately tied to sleep.
Sleep loss can negatively impact the immune system and conversely, an altered immune system can affect our sleep.
So, how does this relationship work, and can we improve our sleep habits for better immune functioning?
What is the Immune System?
The immune system is our natural defense system within the body. It is responsible for attacking and destroying any substance (e.g., a virus, bacteria, or parasite) that it thinks is a threat (i.e., an antigen).
We have three types of immunity:
- Innate: the natural immunity we are born with
- Adaptive: the immunity we develop over time or through vaccination
- Passive: short-term or ‘borrowed’ immunity – e.g., a course of antibiotics
How Does The Immune System Work?
Innate immunity is our first line of defense against anything entering the body or that has entered our body.
In the case of an antigen that enters the body, an immediate but nonspecific innate response occurs. In other words, innate immunity is not good at differentiating something that is threatening (a wound) from something that is not (a clean piercing).
Adaptive immunity is much more specific and is the second line of defense – called upon by the innate system when needed.
When innate or adaptive immunity activates, this is an immune response. Usually, this is due to acute inflammation, whereby blood flow to an infected or damaged region increases, resulting in redness and warmth.
Leukocytes (white blood cells), created in our bone marrow, are the main drivers of any immune response. There are three main types of leukocytes, each with specific functions:
- Basophils (involved in inflammatory and allergic reactions)
- Lymphocytes (the identifiers of threat and bringers of war)
- Phagocytes (the killer cleaners)
Further, there are two main types of lymphocytes involved in this process; T-cells and B-cells.
When the immune system identifies a threat, T-cells multiply (hence why our white blood cell count rises) and release chemicals (known as cytokines) which, in turn, stimulate the production of B-cells.
B-cells produce infection-fighting antibodies which attach themselves to infected or damaged cells, differentiating antigens from normal healthy cells and tissue.
T-cells attack and signal phagocytes to help destroy and consume the remains. Following battle, a few T and B cells that have recognition for that particular antigen replicate in case it reappears, creating something we call ‘immunological memory.’
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The Importance of Sleep
While we might think of sleep as a pretty passive activity, we use up a large amount of energy at night. Instead of using that energy to walk, talk, think and act, as we would in the daytime, we use energy at night to maintain and protect our physical, psychological and emotional health.
This is why we see a consistent long-term relationship between sleep loss and sleep disorder (such as sleep apnea, insomnia, and circadian rhythm disorders). And illnesses such as diabetes, cardiovascular disease, high blood pressure, and obesity.
This link between sleep and health is most evident during Slow Wave Sleep (SWS or deep sleep) instead of REM sleep. REM is good for emotional memory and emotional regulation.
SWS has been strongly linked to several health indicators. This includes glucose regulation, the repair of damaged tissue, the clearance of toxins from the brain, and the regulation of hormones associated with appetite and fertility.
Sleep is also characterized by increased cytokine activity and reductions in stress hormones, such as cortisol. The action of the sleep and immune systems follow a circadian rhythm. And the pattern reverses in the case of poor sleep or sleep deprivation – less cytokine activity during the night and increases in stress hormones.
Another issue with sleep deprivation is that it can influence inflammation with increases in inflammatory cytokines occurring due to sleep loss even without the presence of an antigen. Any unnecessary increase in inflammation can result in tissue damage and contribute to longer-term illness.
How Does Sleep Affect the Immune System?
Considering its importance, there are three main ways in which sleep can impact the innate and adaptive immune system.
In terms of repair, we can already see that insufficient sleep will negatively impact the immune system. Poor sleep results in increased susceptibility to illness. This can then cause increased demands on the immune system and the potential for longer-term disruptions to sleep due to the illness itself (e.g., pain, medication use). And thus, this creates a vicious cycle.
Also, as poor sleep reduces the immune system’s efficiency to respond, the response to a new threat will diminish, thus prolonging recovery. Finally, poor sleep also increases ‘immune self-tolerance’, which is the ability to differentiate healthy cells from antigens. This can destroy healthy cells and allow antigens to remain active within the body.
In terms of response, one study monitored sleep for 14 days in a group of healthy adults before they were infected with rhinovirus. Those reporting shorter sleep durations were more likely to develop a common cold within the next five days.
In a similar study, those who were sleeping less than seven hours were almost three times more likely to develop a cold than those who had slept eight hours or more. Interestingly, in this latter study, poor sleep quality was also associated with developing a cold.
Those who spent more time in bed awake during the night were five and a half times more likely to develop a cold compared to those who spent more time in bed sleeping. One of the ways in which poor sleep impacts immunity is through a protein called integrin. Integrin allows T-cells to stick to damaged or infected cells. When we have not slept well, we produce less integrin.
In terms of protection, several studies have examined the link between sleep and adaptive immunity, mainly through vaccination. Compared to those who underwent sleep deprivation, the immune response to vaccination from Hepatitis (A in one study and B in another) was faster in those who got a good nights’ sleep.
In this instance, and just with other forms of memory, rest can strengthen immunological memory. And so sleep loss is likely to result in poorer immunological memory.
How Can You Improve Sleep and Strengthen Your Immune System?
The primary consideration is getting sufficient sleep, of good quality, at the right time. For healthy sleep, you should prioritize it as you would diet, exercise, or stress reduction. One of the key ingredients here is trying to keep a regular sleep routine. This promotes the immune system to work in tandem with your sleep system.
Making sure you and your environment are ready for bed is also essential for better sleep. Finding ways to relax before you go to bed are essential.
For example, a couple of hours of downtime in the evening, reducing electronic use before bedtime, or reducing caffeine intake. As well as ensuring your bedroom environment is cool, dark, and quiet. Interestingly, a hot bath, about an hour before bedtime is a great way to relax. And it has the added benefit of mimicking the natural onset of sleep.
It is undeniable that a complex bidirectional relationship exists between sleep and the immune system.
When we get good sleep, our immune function knows to monitor and respond to a threat. When we are sick, we need more sleep for the immune system to do its job.
Studies on sleep, immunity, and COVID-19 have yet to publish. But the likelihood is that enough good quality sleep is going to add some protection against getting COVID-19, decrease the severity of and speed recovery from COVID-19, and provide more immediate protection after a COVID-19 vaccine.