If there’s one thing that’s become clear as the pandemic has stretched on, it’s that there’s a lot to be explored in the relationship between Covid-19 and poor sleep.

We already knew the two were linked. An analysis of sleep studies found sleep problems affected approximately 40% of people in the pandemic – and those who caught Covid-19 appeared to have a higher prevalence of sleep problems.

Now, a study suggests if you had sleep problems prior to getting coronavirus, or suffered daily burnout, you have a heightened risk of not only becoming infected with the virus, but also having more severe disease.

Every one-hour increase in the amount of time spent asleep at night was associated with 12% lower odds of becoming infected with Covid-19, according to the study published in the online journal BMJ Nutrition Prevention & Health.

What happened in the study?

Disrupted sleep and work burnout have historically been linked to a heightened risk of viral and bacterial infections, which is why researchers wanted to explore whether there was a link between Covid-19 and sleep issues, as well as stress.

For the study, researchers drew on responses to an online survey for healthcare workers repeatedly exposed to patients with Covid-19 infection. The survey ran from July to September 2020, and was open to workers in France, Germany, Italy, Spain, the UK and the USA. Some 2,884 healthcare workers responded, 568 of whom caught the virus.

Personal details that were shared included: lifestyle, health, use of prescription medication and dietary supplements, plus information on how much sleep they got at night and in naps over the preceding year; any sleep problems; burnout from work; and workplace exposure to coronavirus.

Infection severity was defined as:

• very mild – no or hardly any symptoms;
• mild – fever with or without cough, requiring no treatment;
• moderate – fever, respiratory symptoms and/or pneumonia; 
• severe – breathing difficulties and low oxygen saturation;
• critical – respiratory failure requiring mechanical assistance and intensive care. 

What did researchers find?

On average, respondents were getting between six and seven hours sleep a night. Around one in four of those who’d tested positive for Covid-19 reported difficulties sleeping at night compared with around one in five of those without the infection.

One in 20 (5%) of those with Covid-19 said they had three or more sleep problems, including difficulties falling asleep, staying asleep, or needing to use sleeping pills on three or more nights of the week, compared with 3% of those without the infection.

Compared with those who had no sleep problems, those with three sleep issues had 88% greater odds of Covid-19 infection. Every extra hour of sleep at night was associated with 12% lower odds of Covid-19 infection. 

Workers with daily burnout were around three times as likely to say that their Covid infection was severe and that they needed a longer recovery period.

The study was observational so can’t establish a cause – and there were a few limitations to it, including that assessment of exposure levels, sleep issues, and infection severity, were all subjective (so might’ve been misremembered) and the sample only included cases of very mild to moderately severe Covid-19.

Why might lack of sleep be linked to Covid?

It’s not clear why insomnia and burnout are linked to increased Covid severity, however researchers hypothesised that lack of sleep and sleep disorders may adversely influence the immune system by increasing proinflammatory cytokines and histamines, which could in turn increase disease severity.

They also pointed to studies linking burnout 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. Such studies have suggested that burnout may directly or indirectly predict illnesses by occupational stress impairing the immune system and changing cortisol levels.

Dr Minha Rajput-Ray, medical director of NNEdPro Global Centre for Nutrition & Health, which co-owns the journal Nutrition Prevention & Health with BMJ, said: “This study spotlights an often neglected area of wellbeing: the need for quality sleep and re-charge time to prevent burnout and its consequences.

“A better understanding of the effects of shift work and sleep is essential for the wellbeing of healthcare staff and other key workers.

“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 wellbeing.”