Why Sleep Is So Important for a Healthy Immune System

Your immune system — the body’s key defense against germs and other things that could make you sick — suffers when you don’t get enough sleep.

If you doubt it, consider the findings of a study published in 2015 in the journal Sleep.

Researchers tracked the sleep of 164 volunteers and then purposely exposed them to samples of rhinovirus (the common cold). The more sleep a person had gotten in the days before the exposure, the less likely they were to get sick, the study found. Those who averaged less than five hours of sleep per night were more than twice as likely to get sick as those who slept an average of seven hours or more.

“There’s a lot of truth to the idea that sleep is the best medicine,” says Filip Swirski, PhD, a professor of medicine at the Icahn School of Medicine at Mount Sinai in New York City, who has studied the relationship between sleep and the immune system.

“We know that sleep disruption affects the rhythm and production of immune cells, and if there is a challenge to the immune system (such as an infection or injury), a single night of poor sleep can affect the response,” he says.

Research has shown that people who don’t get enough sleep are at greater risk for both infectious and inflammatory diseases. Here, Dr. Swirski and other experts explain why sleep is so crucial to your body’s immune functioning.

What Is Your Immune System and What Does It Do?

Your body is almost constantly exposed to a wide array of pathogens, which are microorganisms that can make you sick, research tells us. These pathogens are in the food you eat, the air you breathe, and the physical things your body comes into contact with during the day.

Your immune system is responsible for defending you from these pathogens, as well as from any forms of damage or disease that arise in your body. It’s made up of a complicated network of cells and proteins that can identify potential threats and coordinate an appropriate response.

In many cases, that response takes the form of inflammation. Inflammation is one of your immune system’s primary weapons against infection, illness, or injury. However, even when its doing good work, inflammation can cause pain, swelling, and other unpleasant symptoms. Also, as you’ve likely heard, inflammation can sometimes arise inappropriately, in which case it can cause or contribute to sickness or disease, according to StatPearls.

But when you miss out on sleep, your immune system and inflammatory responses are disrupted in some problematic ways.

How Does Sleep Support the Immune System?

For starters, sleep allows your body the opportunity to replenish its immune cells. “These cells are the foot soldiers of the immune system,” Swirski says. “They survey for potential threats and participate in host defense.”

The production of immune cells mostly takes place when you’re sleeping, not when you’re awake, he explains. And when you don’t get adequate sleep, this production is thrown out of whack.

When that happens, one of the consequences can be out-of-control inflammation. “Sleep disturbances or sleep loss can produce a marked increase in inflammation,” says Michael Irwin, MD, a professor of psychiatry and biobehavioral sciences at the David Geffen School of Medicine at UCLA in Los Angeles, who has conducted years of research on sleep and the immune system.

While healthy inflammation can help the body defend itself from threats, Dr. Irwin says that too much inflammation can contribute to the kinds of internal damage or changes that lead to heart disease, diabetes, and some other medical conditions, all of which research has also linked to poor sleep. Too much inflammation can also increase pain, swelling, and other symptoms of chronic diseases, he says.

Finally, researchers have found (and reported in the aforementioned 2015 Sleep study) that, toward the end of a full night of sleep, immune cells migrate out of the blood and into the lymphoid organs, which is where viral pathogens often accumulate after entering the body.

If you don’t get enough sleep, that migration is disrupted, and so your immune cells may not properly engage with those pathogens. This may be one reason why poor sleep is associated with an increased risk for infections or illness.

What’s the Evidence That Sleep Supports Immune Functioning?

Apart from that 2015 study — the one showing that sleep-deprived people are more likely to get sick from the common cold — a lot of research has shown that healthy sleep helps balance and regulate the activity of the immune system.

Studies have also found that good sleep improves the ability of these immune cells to properly attach to their targets.

“If you disturb sleep, you affect the rhythm and production of immune cells, and this can contribute to the development of inflammatory diseases,” Swirski says. To his point, more research in the journal Sleep has found that people with sleep disorders are at greater risk for developing autoimmune diseases, such as rheumatoid arthritis.

A review of research has also linked chronic poor sleep to an increased risk for heart disease, diabetes, and neurodegenerative diseases such as Alzheimer’s. Another review shows evidence that disturbed sleep is a risk factor for many different cancers, as well as for mental health conditions such as depression, research shows.

One night of poor sleep likely won’t make or break your health. But, at this point, it’s clear that if you aren’t sleeping well much of the time, your health is likely to suffer for it.

4 Tips for Sleeping for Healthy Immune Functioning

While guidelines from the National Sleep Foundation recommend adults get seven to nine hours of sleep per night, experts say overall sleep quality may be more important than total sleep time when it comes to a healthy immune system.

1. Focus on Sleep Quality and How Rested You Feel When You Wake up

“Sleep duration is not as big a predictor of inflammation as poor sleep quality,” Irwin says. “We found that you really don’t see an increase in inflammation until you get down to the five- to five-and-a-half-hour range.”

He also says that, even if people are sleeping a solid eight hours a night, that doesn’t necessarily mean that their sleep is deep and supportive of a healthy immune system. “Even among people with adequate sleep duration, if they wake up feeling tired, they report that they’re waking up a lot during the night, or the quality of their sleep is poor, we find all that is associated with increases in inflammation,” he says.

He says one of the best ways to assess your sleep is to ask yourself how you feel in the hours after you wake up. If you feel rested and rejuvenated, that’s a sign that you had a good night’s sleep. “People also turn to devices like Fitbits and Apple watches to assess their sleep, and I’ve found they’re actually very good at determining the quality of your sleep,” he says.

2. Get Better Quality Sleep by Being Consistent

If you want to strengthen your sleep in order to support your immune system, Irwin offers advice that you’ve probably heard elsewhere. “Stick with a consistent sleep-wake routine, get some exercise during the day, and avoid alcohol and caffeine before bed,” he says.

3. Try Practicing Mindfulness

Irwin also recommends mindfulness training. “For a JAMA Internal Medicine study, we gave people six weeks of mindfulness training, and we found improvements in sleep quality,” he says. Since then, another study he published found that using a mindfulness app (specifically, the Calm app) for 10 minutes a day helped decrease daytime fatigue and improve sleep quality.

4. If You Struggle With Sleep, Seek Help

If you are struggling with your sleep, especially if you are snoring, a mouth-breather, or at risk for sleep apnea, it's best to discuss with your primary doctor and potentially be evaluated by a sleep expert (such as a pulmonary or sleep medicine specialist).

Cognitive behavioral therapy for insomnia, or CBT-I, has proven itself to be one of (if not the) most safe and effective insomnia treatments, Irwin says. It’s recommended as first-line treatment for people with insomnia.

Unfortunately, he says there is a lack of qualified CBT-I therapists — not nearly enough to meet demand. “We have a 2,000-person waitlist at our clinic, so it’s a big issue,” he says.

While he says working with a licensed CBT-I practitioner is best, he adds that some web-based programs and apps can serve as a substitute. Insomnia Coach is one CBT-I-based app that clinical trials have linked to sleep improvements.