Sleeping an extra hour each night decreases the chance of catching coronavirus by 12 per cent – but taking a nap in the afternoon raises the risk by six per cent, scientists have found.
US researchers surveyed 2,884 healthcare workers from the UK, France, Germany, Italy, Spain and the US – 568 of whom had had Covid – between July and September.
The researchers found the risk of coronavirus was greater for people who had trouble sleeping and those who were "burned out" by their job.
Every one-hour increase in the amount of time spent asleep at night was associated with 12 per cent lower odds of becoming infected with Covid, the findings indicate.
Disrupted or insufficient sleep and work burnout have previously been linked to a heightened risk of viral and bacterial infections, but it was unclear whether they were also risk factors for Covid.
The survey showed that the average amount of sleep the participants had was between six and seven hours. Although more sleep at night appeared to be protective, an extra hour of daytime napping was associated with six per cent higher odds of being infected with Covid.
Compared with those who had no sleep problems, people who reported difficulties in falling or staying asleep, or needed to use sleeping pills, had 88 per cent greater odds of a Covid infection.
The researchers, from Stamford Hospital in Connecticut, hypothesised that lack of sleep and sleep disorders can influence the immune system, increasing inflammatory molecules.
Burnout has been linked to a heightened risk of colds and flu as well as long-term conditions such as diabetes, cardiovascular disease, musculoskeletal disease and death from all causes.
"This study spotlights an often neglected area of well-being – the need for quality sleep and recharge time to prevent burnout and its consequences," said Dr Minha Rajput-Ray, the medical director of the NNEdPro Global Centre for Nutrition and Health, which co-owns the journal with BMJ.
"Disruptions to the sleep-wake cycle can affect metabolic, immune and even psychological health. And sleep deprivation can make calorie dense foods, higher in fat, sugar and salt, more appealing, particularly during times of stress and/or difficult shift patterns, all of which takes a toll on overall health and well-being."
The research was published in the journal BMJ Nutrition Prevention & Health.