You probably know the feeling. You wake up foggy after a short night, and by the end of the week someone in the office is coughing. It can feel like the two things are not really connected.
They may be more connected than you think. A controlled trial published in SLEEP in 2015 found that healthy adults who slept fewer than 6 hours a night were more than 4 times as likely to catch a cold as those who slept 7 hours or more.
Researchers at Carnegie Mellon University and UCSF did not simply ask participants if they got sick.
They dripped a live cold virus into every nose and watched what happened over the following days in a hotel.
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How the trial measured sleep and infection
For 7 nights before anyone was exposed, 164 healthy adults wore a wrist monitor that tracked how much they actually slept, not how much they thought they slept. They also kept a sleep diary.
The team then gave nasal drops with rhinovirus, the virus behind most common colds.
They watched for signs of infection over 5 days of quarantine, with daily nasal samples and objective illness markers.
Compared with people who slept more than 7 hours a night, those sleeping under 5 hours had about 4.5 times the odds of coming down with a cold.
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The 5 to 6 hour group was close behind, at about 4.2 times the odds.
Sleep carried more weight than anything else the researchers measured.
"Sleep goes beyond all the other factors that were measured," said Aric Prather of UCSF, the study's lead author.
Age, stress, income, education and smoking were all taken into account, and sleep still stood out.
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Why short sleep seems to weaken immune defense
Your immune system does a lot of its heavy lifting while you are asleep.
Certain immune cells multiply overnight, and the body releases cytokines, small proteins that help coordinate the response to infection.
When sleep is cut short, that nightly work gets squeezed. The authors noted that losing sleep shifts the body away from a T-cell response that normally helps fend off viruses. That may leave the body a step behind when a cold virus arrives.
What 7 or more hours a night looks like in practice
The CDC recommends adults aged 18 to 60 get at least 7 hours of sleep a night.
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For most people that means being in bed closer to 8 hours, since no one falls asleep instantly and nearly everyone wakes briefly during the night.
A consistent bedtime is the simplest lever. Keeping the bedroom cool and dark, and limiting late caffeine, are what sleep doctors keep coming back to in the lead-up to cold and flu season.
If you catch yourself regularly running on under 6 hours, the trial points to that band as where the risk climbs most sharply.
Even shifting bedtime one hour earlier moves you toward the group that stayed well.
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This article is made and published by Mie Hermansen, who may have used AI in the preparation.