The short answer
In a trial where 164 healthy adults were given a cold virus, those who had slept under 6 hours a night the week before were about four times as likely to develop a cold as those who slept over 7 hours. Short sleep has also been linked with weaker responses to flu and hepatitis B vaccines.
Moderate evidence
Trials point the same way but are small or few, or large long-term studies agree but cannot prove cause and effect. How we grade
On this page
The cold virus trial
The best evidence comes from a study at Carnegie Mellon University. Researchers measured the sleep of 164 healthy adults aged 18 to 55 for a week using wrist monitors and sleep diaries. They then put them in quarantine, gave them nose drops containing a common cold virus (rhinovirus), and watched them for five days.
| Sleep in the week before | Chance of a cold compared with over 7 hours |
|---|---|
| Under 5 hours | About 4.5 times as likely |
| 5 to 6 hours | About 4.2 times as likely |
| 6 to 7 hours | No clear difference |
The results held after allowing for age, season, body weight, stress and existing immunity to the virus. Because sleep was measured before anyone was exposed, the cold can’t have caused the poor sleep. But people weren’t randomly assigned to sleep less, so other differences between short and long sleepers could play a part. The study was also small, so the exact figures are uncertain.
What about vaccines?
Two studies point the same way:
- Flu vaccine. In a small lab study, healthy young men who were limited to 4 hours of sleep a night for six nights before a flu jab had antibody levels less than half as high 10 days later as men who slept normally. The difference narrowed over the following weeks.
- Hepatitis B vaccine. In 125 healthy adults aged 40 to 60 having the standard three-dose course, those who slept less, measured with wrist monitors, made fewer antibodies and were less likely to be clinically protected six months after the last dose.
Does poor sleep cause inflammation?
A review of 72 studies with more than 50,000 people found that disturbed sleep was linked with higher blood levels of two inflammation markers, CRP and IL-6. Long-term low-level inflammation is linked with heart disease, diabetes and other conditions. Interestingly, very long sleep was linked with higher levels too, which again may reflect illness.
How strong is the evidence?
Moderate. The cold-virus study measured sleep before infection and the vaccine studies are consistent, and lab work shows plausible mechanisms. But the studies are small and none randomly assigned people to sleep less for weeks. There’s no evidence that sleeping more than about 7 hours gives extra protection.
What does this mean in practice?
Regularly getting 7 hours or more is a sensible part of staying well through the winter. If you can, avoid a run of short nights around a planned vaccination. And if long-term insomnia is cutting your sleep, it is worth treating: see CBT for insomnia.
Keep reading
- Sleep, memory and concentration: what the research shows
How lack of sleep affects attention, reaction time and memory, why sleep after learning helps memories stick, and what that means for students and drivers.
Strong - Sleep and mental health: depression, anxiety and mood
How poor sleep is linked with depression and anxiety, and what a trial of nearly 4,000 UK students found about treating insomnia to help mental health.
Moderate - Sleep and type 2 diabetes: how short sleep affects blood sugar
How short and broken sleep are linked with type 2 diabetes, what lab trials show about blood sugar control after sleep loss, and why sleep apnoea matters.
Moderate
Common questions
Does sleep help you get over a cold?
Resting and sleeping when you're ill is sensible and is what the NHS advises, and the immune system is active during sleep. But there are no good trials showing that extra sleep shortens a cold.
Should I sleep well before a vaccine?
It is a reasonable thing to aim for. Studies have found weaker antibody responses in people who slept little in the days around their vaccination. Don't skip a vaccine because of a bad night, though: you'll still be well protected.
Why do I get ill when I'm run down?
Short sleep, stress and overwork all affect the immune system. In virus-exposure studies, both short sleep and high stress made people more likely to develop a cold once infected.
References
- Prather AA et al. Behaviorally assessed sleep and susceptibility to the common cold. Sleep, 2015.pubmed.ncbi.nlm.nih.gov
- Spiegel K, Sheridan JF, Van Cauter E. Effect of sleep deprivation on response to immunization. JAMA, 2002.pubmed.ncbi.nlm.nih.gov
- Prather AA et al. Sleep and antibody response to hepatitis B vaccination. Sleep, 2012.pubmed.ncbi.nlm.nih.gov
- Irwin MR et al. Sleep disturbance, sleep duration, and inflammation: a systematic review and meta-analysis. Biological Psychiatry, 2016.pubmed.ncbi.nlm.nih.gov
First published 4 November 2026. Spotted an error? Tell us and we'll correct it. Read our editorial policy.