Your immune system makes you sleepy on purpose, and sleep returns the favor

Key takeaways

• In a 2003 German study, adults who slept the night after a hepatitis A shot had nearly twice the antibody level four weeks later as those kept awake¹.
• Immune signaling molecules such as IL-1 and TNF help regulate normal sleep, and during an infection they reshape it in ways researchers think help the body run a fever⁵.
• In a 2019 lab study, immune T cells from sleeping volunteers stuck to their targets better than those from people kept awake, and three hours without sleep was enough to blunt them⁷.
• In a U.S. survey of 22,726 adults, 5.9% of people who slept five hours or less reported an infection such as flu or pneumonia in the past month, versus 3.3% of 7- to 8-hour sleepers; a survey can’t prove cause⁸.
• Night-shift research is mixed: a Dutch hospital study found about 20% more respiratory infections in night workers, but a 2025 review found no clear rise in colds and flu¹⁰¹¹.

In a study published in 2003, researchers at the University of Lübeck in Germany gave 19 healthy adults a hepatitis A vaccine at 9 a.m. That night, some went to bed as usual. The others were kept awake until 9 p.m. the next day¹.

Four weeks later, the people who had slept had nearly twice the level of hepatitis A antibodies as those kept awake¹. One ordinary night of sleep, at the right moment, seemed to change how well the body learned from the shot.

The link runs the other way, too. When you’re sick and can barely keep your eyes open, it can feel like your body is giving up. Scientists see it differently: immune signals pull you toward sleep, and that sleep appears to support the fight⁵⁶.

If you grew up being told to go to bed when you were ill, the research backs that advice more than you might expect. Below, we look at what’s known about the two-way link, what it means around vaccines for people who choose them, and how shift workers, new parents, older adults and hospital patients can protect their sleep.

Feeling wiped out when you’re sick is your immune system at work

When your body detects an infection, immune cells release signaling proteins called cytokines. Two of them, interleukin-1 (IL-1) and tumor necrosis factor (TNF), also help regulate normal non-REM sleep, the stages that include deep sleep⁵. That’s according to a 2009 review in Nature Reviews Neuroscience by Luca Imeri and Mark Opp.

During an infection, those signals grow stronger and sleep changes shape. Non-REM sleep gets broken up, and REM sleep, the stage tied to vivid dreams, is suppressed⁵.

Sleepiness is one piece of what researchers call sickness behavior. The rest includes eating less, moving less, losing interest in usual activities and letting self-care slide⁵. Imeri and Opp proposed that the sleep changes are fine-tuned to help the body produce a fever, which has survival value⁵.

Animal data hint at the stakes. In an analysis of almost 100 rabbits, those that slept better during infections were more likely to survive⁵. That’s rabbits, not people, and it shows a link, not proof.

A 2019 review in Physiological Reviews, by Luciana Besedovsky, Tanja Lange and Monika Haack, describes the relationship as a two-way street⁶. Depending on how strong an inflammatory response is and how it unfolds, it can lengthen and deepen sleep or break it up. Extra sleep during an infection is thought to feed back and support the body’s defenses⁶.

That fits a value many natural-health readers hold: the body has its own healing wisdom, and rest is part of it. When you’re sick, let yourself sleep.

Sleep the night after a shot changed how the body responded

The Lübeck team followed up in 2011 with 27 healthy men who got three hepatitis A shots, at weeks 0, 8 and 16². After each shot, they either slept or stayed awake that night. Researchers tracked them for a year².

Sleep roughly doubled the number of “helper” T cells that recognized the vaccine. It also raised a vaccine-specific type of antibody called IgG1². The boost was strongest in men whose brain waves showed more slow-wave activity, the signature of deep sleep, that night².

Hormones may help explain it. Sleep after the shot raised growth hormone and prolactin and lowered stress hormones: adrenaline and noradrenaline in the 2003 study, cortisol in the 2011 study¹². The 2019 review names a supportive hormone profile during sleep as a likely reason sleep helps immune function⁶.

Earlier work pointed the same way. A 2002 University of Chicago flu-shot study of young men on nearly a week of badly shortened sleep found a weaker early antibody response, a result our sleep-debt article walks through³.

Co-author Eve Van Cauter, a University of Chicago sleep researcher, took a practical lesson from it: try to be well rested when you’re vaccinated. She singled out older adults and shift workers³.

Everyday sleep at home matters too. In a 2012 study led by Aric Prather, 125 midlife adults got the three-dose hepatitis B series. Their sleep was tracked by self-report and with wrist monitors. Sleeping under six hours a night was linked to a lower chance of being protected⁴.

Keep the limits in view. These studies were small, mostly in healthy men, and they measured antibodies and immune cells rather than who later got sick. Our immune-boosting article covers a 2023 pooled analysis of this research.

None of this says whether you should get a particular vaccine. That decision is yours, ideally made with a clinician you trust. Our article on vaccine schedules explains how the competing schedules differ, and a later article in this series covers vaccines in depth.

Whatever you decide, the same sleep is linked to lower infection risk and better outcomes when infections strike, the 2019 review reports⁶.

While you sleep, T cells get a better grip

T cells are immune cells that hunt infected cells. To kill a virus-infected cell, a T cell first has to latch onto it, using sticky proteins called integrins⁷.

In a 2019 study published in the Journal of Experimental Medicine, researchers at the Universities of Tübingen and Lübeck ran a 24-hour experiment⁷. One group of volunteers slept eight hours at night. The other stayed awake. Blood samples were taken throughout⁷.

T cells from the sleepers showed more integrin activation⁷. Just three hours without sleep was enough to reduce the cells’ ability to stick. When the team added blood plasma from awake volunteers to isolated T cells, the cells’ grip weakened after just a few minutes⁷.

The likely culprits were adrenaline, noradrenaline, prostaglandins and adenosine, all of which blocked integrin activation in the lab. Both adrenaline and prostaglandins run lower while you sleep⁷. The researchers suggested the finding might matter for sleep disorders, depression, chronic stress, aging and shift work, but that hasn’t been tested⁷.

Over the long run, the 2019 review adds, ongoing short or disturbed sleep can cause chronic low-grade inflammation, which is tied to diabetes, hardened arteries and diseases in which brain cells die off⁶.

Short sleepers and night workers report more infections, but the data are mixed

A large real-world look comes from the National Health and Nutrition Examination Survey. In 2016, Aric Prather and Cindy Leung of the University of California, San Francisco, analyzed 22,726 adults surveyed from 2005 to 2012⁸. About 13.6% said they usually slept five hours or less on weekdays⁸.

In the past 30 days, 19.0% of those short sleepers reported a head or chest cold, versus 15.5% of people sleeping seven to eight hours. And 5.9% reported an infection such as flu, pneumonia or an ear infection, versus 3.3%⁸.

By our math, that’s about 35 more colds and 26 more infections per 1,000 people, before accounting for other differences. After adjusting for factors such as age, income, smoking, activity and body mass index, short sleepers still had 17% higher odds of a cold and 51% higher odds of an infection⁸.

Six-hour sleepers and people sleeping nine hours or more showed no clear difference⁸. The study relied on people’s own reports at one point in time, so it can’t show that short sleep caused the infections⁸. Illness can also disrupt sleep, the authors noted. The National Institutes of Health funded the work⁸.

The National Center for Complementary and Integrative Health (NCCIH) puts the takeaway plainly: poor sleep may lower your resistance to infections¹³.

Night shifts add another layer. In a 2019 Dutch study, 589 hospital workers logged symptoms daily on a phone app from September 2016 to June 2017, for 110,347 entries in all⁹. Shift workers had flu-like or respiratory infections at 1.20 times the rate of non-shift workers, and severe episodes at 1.22 times the rate⁹. RIVM, the Dutch public health institute, reported that night workers averaged about 3 to 4 episodes per winter, versus 2 to 3 for day workers¹⁰.

A 2025 review from the same lead author covered 14 studies of 191,320 workers¹¹. Night-shift work wasn’t clearly linked to colds and flu, based on 4 studies. It was linked to higher odds of COVID-19 infection, based on 10 studies¹¹. The reviewers rated the certainty of all this as very low¹¹.

New parents, older adults and hospital patients

New parents. We found no study measuring how a newborn’s night feedings affect a parent’s immune defenses. What follows are our suggestions, built on the findings above, not tested advice.

If two adults share the nights, trade off so each gets one longer stretch of sleep, and nap when you can. If you plan a vaccine for yourself, a day after a better night is a sensible choice.

Older adults. Van Cauter noted in 2002 that flu shots tend to work less well in older people, and that little was known about their sleep needs³. A companion article on immunity across the lifespan covers how the aging immune system changes.

Hospital patients. Hospitals are hard places to sleep. A 2017 study measured sound in 24 rooms on general wards, heart-monitoring units and intensive care units¹⁴. Average hourly levels ran 45 to 54 decibels on general wards and 56 to 60 in intensive care units. World Health Organization guidance calls for under 35 decibels by day and under 30 at night¹⁴.

Every location broke those limits at every hour¹⁴. Morning light was also likely too dim to help set the body clock, the editorial noted. The study didn’t link its readings to patients’ sleep or health, so those effects remain unproven¹⁴.

If you’re staying in a hospital, you can ask about earplugs or an eye mask and whether lights can stay low at night. Our article on bedroom noise covers what intensive care studies found with earplugs.

Melatonin isn’t an immune fix

Melatonin, a hormone sold as a sleep supplement, has drawn interest as a possible COVID-19 treatment. NCCIH says that research is only beginning and it’s too soon to draw conclusions¹².

NCCIH considers short-term use safe for most people but says long-term safety data are lacking¹². Anyone with epilepsy, or on a blood thinner, should use it only under a clinician’s watch. Pregnancy safety hasn’t been studied well, and in older adults the hormone can linger into the next day and cause drowsiness¹².

Quality is another problem. A 2023 study found that 22 of 25 melatonin gummy products were mislabeled. One held no melatonin, and the rest held 74% to 347% of the labeled amount¹². Our melatonin article covers its real uses for body-clock timing.

The sleep-and-immunity plan

This plan is our own design. It sorts practical steps by situation, with an honest evidence rating for each.

Situation	What helps	Evidence rating
The days around a vaccine you’ve chosen	Get a full night before and especially after the shot; avoid all-nighters and red-eye trips that week123	Promising but early
When you’re sick	Let yourself sleep more and rest; it’s part of the immune response56	Promising but early (mostly lab and animal work)
Night or rotating shifts	Protect one main sleep block; our shift-work articles cover treatment for shift work disorder	Not enough evidence for immune outcomes911
A new baby at home	Trade off nights and nap when possible (our suggestions)	Not enough evidence (no studies found)
A hospital stay	Ask about earplugs, an eye mask and low night lighting	Not enough evidence for immune outcomes14
Melatonin “for immunity”	Skip it for this purpose; ask a clinician if you take medicines	Not enough evidence12

What the evidence says

Claim	Evidence rating	What it rests on
Infection and immune signals reshape sleep	Strong evidence	Two major reviews of lab, animal and human research56
Sleep the night after a vaccine strengthens the immune response	Promising but early	Small lab studies, mostly in healthy men123
Short sleep around vaccination means weaker protection	Promising but early	One study of 125 adults4
Sleep helps T cells stick to infected cells	Promising but early	One lab study7
Short sleepers get more infections	Promising but early	Large survey; can’t prove cause8
Night-shift work raises colds and flu	Not enough evidence	One cohort found more; a review found no clear rise, very low certainty911
Melatonin helps prevent or treat infections	Not enough evidence	NCCIH: too soon to say for COVID-1912

When to get care

Sometimes poor sleep is a medical problem. NCCIH says to talk with a health care provider if you have possible signs of sleep apnea, a condition where breathing stops or turns very shallow during sleep¹³:

• loud snoring;
• a bed partner noticing gasping or snorting sounds;
• fighting off sleepiness during the day¹³.

For flu, CDC’s symptoms page, last reviewed in August 2024, lists emergency warning signs that call for medical care right away. In adults, they include trouble breathing or shortness of breath, chest or belly pain or pressure that doesn’t let up, dizziness or confusion that won’t clear, being hard to wake, seizures, not urinating, severe muscle pain or weakness, and a fever or cough that improves and then returns or worsens¹⁵.

In children, the list adds fast or labored breathing, a bluish tint to the lips or face, ribs that pull in with each breath, signs of dehydration such as no urine for 8 hours, not being alert when awake, a fever above 104°F that fever reducers don’t bring down, and any fever in a baby under 12 weeks old¹⁵. At any age, a chronic illness that gets worse is a warning sign too, and CDC notes its lists aren’t complete¹⁵. Our article on symptoms that mean call 911 covers when to call an ambulance.

Questions readers ask

The bottom line

Sleep and immunity work as partners. Immune signals make you sleepy when you’re fighting an infection, and sleep, in turn, seems to help immune cells grip their targets and learn from vaccines. Most of that evidence comes from small lab studies and surveys, so treat it as promising, not settled.

The practical steps cost nothing. Rest when you’re sick, protect your sleep around a vaccine you’ve chosen, guard a main sleep block if you work nights, and see a clinician for signs of sleep apnea or a serious infection.

Related reading

• Your immune system works more like a team than a volume knob, and some habits help it
• Two weeks of six-hour nights can impair you like an all-nighter
• How to read competing vaccine schedules now that the advice has split
• Shift work disorder is treatable, though even the approved pills leave you sleepy
• Sleep apnea care now goes well beyond CPAP, and mouth tape isn’t part of it

Sources

1. Lange T, Perras B, Fehm HL, Born J. “Sleep Enhances the Human Antibody Response to Hepatitis A Vaccination.” Psychosomatic Medicine, 2003;65(5):831-835 (University of Lübeck research record). research.uni-luebeck.de
2. Lange T, Dimitrov S, Bollinger T, Diekelmann S, Born J. “Sleep After Vaccination Boosts Immunological Memory.” Journal of Immunology, 2011;187(1):283-290 (University of Lübeck research record). research.uni-luebeck.de
3. HealthDay. “Want a Flu Shot? Get Some Sleep First” (on Spiegel K, Sheridan JF, Van Cauter E, “Effect of Sleep Deprivation on Response to Immunization,” JAMA, 2002;288:1471). September 24, 2002. healthday.com
4. Irwin MR. “Sleep and Infectious Disease Risk.” Sleep, 2012;35(8):1025-1026 (editorial on Prather AA, et al., Sleep, 2012;35(8):1063). pmc.ncbi.nlm.nih.gov
5. Imeri L, Opp MR. “How (and Why) the Immune System Makes Us Sleep.” Nature Reviews Neuroscience, 2009;10:199-210. nature.com
6. Besedovsky L, Lange T, Haack M. “The Sleep-Immune Crosstalk in Health and Disease.” Physiological Reviews, 2019;99(3):1325-1380 (Beth Israel Deaconess Medical Center research record). pubmed.ncbi.nlm.nih.gov
7. Rockefeller University Press. “German Researchers Discover How Sleep Can Fight an Infection.” Newswise, February 6, 2019, newswise.com; and University of Lübeck press release on the same study, uni-luebeck.de (both on Dimitrov S, et al., Journal of Experimental Medicine, 2019;216:517).
8. Prather AA, Leung CW. “Association of Insufficient Sleep With Respiratory Infection Among Adults in the United States.” JAMA Internal Medicine, 2016;176(6):850-852. pubmed.ncbi.nlm.nih.gov
9. Loef B, et al. “Shift Work and Respiratory Infections in Health-Care Workers.” American Journal of Epidemiology, 2019;188(3):509-517 (Utrecht University repository). dspace.library.uu.nl
10. National Institute for Public Health and the Environment (RIVM), Netherlands. “More Influenza-Like and Respiratory Complaints in Night-Shift Workers in Hospitals.” News release on the 2019 study (undated page).
11. Loef B, Bosma E, van Kerkhof LWM, Proper KI, van Baarle D, Dollé MET. “Night-Shift Work and Susceptibility to Infectious Diseases: A Systematic Review and Meta-Analysis.” Scandinavian Journal of Work, Environment & Health, 2025;51(4):298-311 (RIVM repository). pubmed.ncbi.nlm.nih.gov
12. National Center for Complementary and Integrative Health. “Melatonin: What You Need To Know.” NIH, updated May 2024. nccih.nih.gov
13. National Center for Complementary and Integrative Health. “Sleep Disorders and Complementary Health Approaches: Usefulness and Safety.” NIH, updated May 2024. nccih.nih.gov
14. Kamdar BB, Martin JL, Needham DM. “Noise and Light Pollution in the Hospital: A Call for Action.” Journal of Hospital Medicine, 2017;12(10):861-862 (editorial on Jaiswal SJ, et al., Journal of Hospital Medicine, 2017;12(10):798-804). pubmed.ncbi.nlm.nih.gov
15. Centers for Disease Control and Prevention. “Signs and Symptoms of Flu.” CDC, last reviewed August 26, 2024. cdc.gov