Sleep and the immune system

If your eyes feel heavy when you’re a bit under the weather, it’s not just you. Many people feel sleepy and tired when sick. Not surprisingly, research has shown that sleep and the immune system are connected and have a bidirectional relationship. Sleep makes your immune system more effective and immune cells promote sleep.¹

You’ve probably heard that sleep is the best medicine when you’re not feeling well. When you feel unwell and fall asleep, your immune system gets to work to fight off the infection. Keep reading to learn about how your immune system works, what it does while you sleep, and what happens to it when you don’t get enough sleep.

What is the immune system, and how does it work?

Your immune system is your body’s defense against infection. It works constantly to keep your body healthy and fight off anything that tries to throw it off balance.

Your immune system is made up of a group of white blood cells and lymph nodes, as well as your spleen, tonsils and adenoids, thymus, bone marrow, skin and mucous membranes, and gastrointestinal tract.² All of these work together to fight off harmful invaders.

Your immune system is categorized into the two systems:

the innate immune system and

the adaptive immune system

Innate immune systemYour innate immune system is your body’s first line of defense against foreign invaders. It is not specific to a particular pathogen but quickly recognizes the general properties of invaders.³ It produces a rapid response, usually within minutes or hours after recognizing an invader.⁴ Physical barriers like your skin and mucous membranes are part of your innate immune system. But when pathogens get past these roadblocks, your innate immune system activates cells such as phagocytes (macrophages and neutrophils), dendritic cells, mast cells, basophils, eosinophils, natural killer (NK) cells, and lymphocytes (T cells).³

Adaptive immune system

The next line of defense in your immune system is your adaptive immune system (or acquired immune system). Your adaptive immune system is the part of your immune system that has learned over time to be highly specific to the particular invader present.⁵

Unlike your innate immune system, your adaptive immune system does not produce an immediate immune response the first time it sees a pathogen. Instead, it memorizes specific antigens (substances on the surface of pathogens) so that it can attack them when they come back on the scene.⁶

Your adaptive immune system consists of white blood cells called lymphocytes. The lymphocytes involved in your adaptive immune system are B cells and T cells.

B lymphocytes become cells that produce antibodies. Antibodies function by attaching to specific antigens on harmful cells or substances so that other immune cells can target and destroy these antigens.⁶

T lymphocytes have the important function of attacking antigens directly. They also release chemicals called cytokines that are important for modulating the entire immune response.⁶

Your adaptive immune system complements your innate immune system, working hand-in-hand.³

What does your immune do while you sleep?

The four stages of sleep are divided into two phases: non-rapid eye movement (non-REM or NREM), which has three stages, and REM sleep. After you fall asleep, your body begins to cycle through the stages of NREM and REM sleep.⁷ NREM sleep makes up most of your sleep time.⁸

Your immune system is mostly triggered in stage 3 (NREM) sleep, also known as deep sleep.⁹ During NREM sleep, bodily processes like your metabolism slow down, giving your immune system more energy to fight infection.¹⁰ When you don’t get enough sleep, your immune system has to work overtime to keep you healthy.

Here’s what your immune system is doing during the different stages of sleep

• Stage 1 NREM sleep:This is the first stage of sleep. Your eye movement and muscle activity start to slow down. Your immune system hasn’t kicked in yet.⁷

• Stage 2 NREM sleep:You are still in light sleep. Your eye movement stops, your heart rate slows, and your body temperature decreases. Your body is preparing to go into deep sleep.⁷

• Stage 3 NREM sleep:You enter deep sleep. Your brain produces delta waves, which are very slow brain waves. You have no eye movement or muscle activity, and it’s hard for anyone to wake you up. It’s in this stage of sleep that your immune system gets the most energy.⁷

What happens to your immune system when you don’t get enough sleep?

Put simply, your immune system doesn’t get the energy it needs.

Sleep puts your body in a restful and non-stressed state. Your metabolic reactions slow down to allow your immune system to repair any cell damage.¹⁴
Scientists believe that the metabolic rate reduces by about 15% during sleep.¹⁴ But if you don’t get enough sleep (particularly NREM sleep), your body’s metabolism won’t slow down enough to transfer energy to your immune system.

Lack of sleep means your immune system can’t keep up.

One of the primary functions of the T cells in your immune system is to produce different kinds of cytokines, which are important stimulators of immune function. If you’re not getting enough sleep, your T cells won’t make optimal levels of cytokines.

In one study, researchers restricted the time allowed for sleep to just four hours for one night in some participants, which decreased NK cell (a subset of T cells) activity in those participants; interestingly, after a night of resumed sleep, NK cell activity returned to baseline levels.¹⁵ Therefore, even a modest amount of sleep loss can impact healthy immune function.

Your immune system can get stuck in “attack” mode.

If you struggle to sleep well at night, this increases stress, which can increase your blood pressure. When this happens, the physical stress on your blood vessels can cause an inflammatory response. High blood pressure causes overproduction of inflammatory mediators, which disrupt the balance of T cells and can trigger your body to go into attack mode, rather than provide protection.¹⁶

However, the more immersed you are in deep sleep, the more time your immune system has to fight infections. This explains why you may have increased sleepiness when you have an infection. It’s also why you may feel refreshed when you eventually wake up from a good mid-day nap or night-time sleep when you’re sick.

Experts have established that sleep and the immune system are connected—the better your sleep hygiene, the more effective your immune system, and vice versa. Your innate and adaptive immune systems are constantly working together to fight infections and sleeping complements their efforts.¹¹

Sleep is truly the best medicine when you’re sick. When you don’t feel well, the best thing you can do is get sufficient rest. Before you sleep, eliminate all distractions and ensure you are in a calming environment. You don’t want to miss the opportunity for your body to go into deep sleep, the stage of sleep where your immune system gets the most energy.

*These statements have not been evaluated by the U.S. Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.