Can good sleep actually strengthen your immune system?

Whenever I come down with a cold, my mom, who’s diligent about getting eight hours of shuteye a night, immediately blames my poor sleep. She’s right that I struggle to fall, and stay, asleep; I usually take an hour to doze off and awaken a few times a night. But could better sleep have prevented me from getting sick? Does good sleep really strengthen your immune system?

The short answer: yes. According to the experts I spoke to, there’s plenty of evidence that a lack of good sleep increases your susceptibility to infection. This happens because sleep quality can affect your immune system’s ability to respond to viruses, bacteria, and other foreign invaders.

Let’s back up, though. What does “good” sleep even look like? First of all, it looks like getting enough sleep, or 7 to 9 hours a night for most adults, Syed Hassan, a research fellow in medicine at Brigham and Women’s Hospital, tells Mic. When you get those hours also matters, says Phyllis Zee, director of the Center for Circadian and Sleep Medicine at Northwestern University Feinberg School of Medicine. Maybe you’re a morning lark, night owl, or somewhere in between; good sleep involves sleeping and awakening according to your natural clock.

An easy way to tell whether you slept well the night before: how you feel during the day.

High quality sleep also entails a solid sleep architecture: Your body cycles through four stages of sleep — Stages 1, 2, and 3, and REM sleep — about every 90 minutes, says Daniel Bessesen, director of the CU Anschutz Health and Wellness Center and chief of endocrinology at Denver Health. Ideally, these cycles would proceed uninterrupted; in other words, you don’t want to wake up at night and take forever to fall back asleep. Otherwise, not only have you not slept enough, but your sleep was “broken up into pieces.”

An easy way to tell whether you slept well the night before is how you feel during the day. “Are you falling asleep during the day when you don’t want to?” Zee suggests asking yourself. “Can you not concentrate? Are you irritable? Is your mood altered? All of these could be signs of not getting a sufficient amount or quality of sleep.”

A bunch of evidence supports the link between sleep and immune function. Hassan points to studies showing that when animals were infected by bacteria, those that had insufficient, interrupted sleep tended to die more than those with good sleep. And when researchers gave a flu vaccine to two groups of healthy human patients — those who were sleep-deprived and those who weren’t — the sleep-deprived patients had an impaired immune response 10 days after vaccination. Specifically, they produced fewer proteins known as antibodies that recognize the flu virus, Zee explains. Studies of people deprived of sleep after getting vaccinated against hepatitis A, hepatitis B, and swine flu yielded similar results.

Research has proven a number of ways poor sleep can wreak havoc on your immune system. Several studies show that sleep deprivation increases the amount of disease-fighting white blood cells and other immune cells in the blood. It’s thought that, instead of residing in tissues like the spleen and lymph nodes, where they need to be to fight infection, “sleep deprivation moves them into the blood, where they’re not helping fight infection anymore,” Hassan explains.

He adds that the first of half sleep favors the production of pro-inflammatory proteins, important for defense against foreign invaders, which gets balanced out by the production of anti-inflammatory proteins during the second half. Sleep deprivation could tip this balance toward a pro-inflammatory response, likely with harmful health consequences long-term. Human studies have also shown that sleep deprivation lowers the activity of natural killer cells, which destroy virus-infected cells. Others suggest that sleep enhances the ability of immune cells known as leukocytes to migrate to sites of infection, while sleep deprivation impairs their function.

Not only can sleep affect your immunity, but when your immune system is fighting an infection, it produces chemicals like cytokines that make you crave sleep.

Meanwhile the vaccination studies indicate that “sleep could enhance your immunological memory,” Hassan says — in other words, the ability of your immune system to “remember” an invader it’s encountered in the past, so that it can mount a quick, targeted attack the next time it makes an appearance. Some scientists hypothesize that deep, restorative Stage 3 sleep is important to this memory, Bessesen says.

Bessesen adds that the relationship between sleep and immunity goes both ways. Not only can sleep affect your immunity, but when your immune system is fighting an infection, it produces chemicals like cytokines that make you crave sleep. Rather than fueling the muscles and keeping you active, “it may be that the body is diverting energy to the immune system,” he says.

To promote good sleep, Zee recommends exercise, which can not only increase your drive to sleep but also improve your immune function. She also suggests situating yourself near a window or other source of natural light, or at least a bright indoor light, in the daytime, and dimming the lights in the evening. While the wellness world might evangelize about dubious supplements purported to boost immunity, sleep is a much simpler — and evidence-based — solution.