People who struggle to sleep or endure work-related burn-out may be more likely to catch the coronavirus, research suggests.
Insomnia and stress have been linked to a higher rate of bacterial and viral infections in general, however, how they affect the coronavirus' onset was less clear.
Results suggest that for every additional one hour of sleep a night, the risk of catching the coronavirus reduced by 12%.
The workers who reported daily burn-out were also more than twice as likely to catch the infection than their less-stressed counterparts.
Although unclear why this occurred, insomnia and chronic stress have been linked to inflammation and an impaired immune system.
The scientists analysed online surveys completed by healthcare workers who were repeatedly exposed to the coronavirus, like those in emergency or intensive care settings.
The survey – which ran from 17 July to 25 September 2020 – was open to all healthcare workers in the UK, US, France, Germany, Italy and Spain.
Questions covered the workers' lifestyle and underlying health.
Of the more than 2,800 respondents, 568 had the coronavirus, confirmed via a test or self-reported following tell-tale symptoms.
All the coronavirus cases were very mild – no or very few symptoms, or moderately severe. A moderate infection was defined as a fever and respiratory symptoms, with or without pneumonia. The scientists classed a severe case as breathing difficulties with low oxygen levels in the blood.
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The results – published in the journal BMJ Nutrition Prevention & Health – reveal just under a quarter (24%) of those with the coronavirus reported sleeping difficulties, versus one in five (21%) without the infection.
One in 20 (5%) of those with the coronavirus had three or more sleep problems, including difficulty nodding off, waking in the night, or requiring sleeping pills at least three nights a week. This is compared to just 3% who did not have the infection.
In comparison to those who had no sleep problems, the workers with three related issues were 88% more likely to catch the coronavirus, the results suggest.
Perhaps surprisingly, napping was linked to a 6% higher risk of the infection on average.
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When it came to burn-out, 5.5% who reported enduring the syndrome every day had the infection. This is compared to 3% with burn-out, but not the coronavirus.
The World Health Organization recognises burn-out as an "occupational phenomenon", defined as "a syndrome resulting from chronic workplace stress that has not been successfully managed". This leads to low energy, "feelings of negativism or cynicism" towards your job and reduced "efficacy" at work.
While burn-out is not considered a medical condition in its own right, stretching yourself too thin can "influence health status or contact with health services".
The burnt-out workers were also over three times more likely to call their infection severe and faced over twice the odds of a "long duration" of infection, the results suggest.
The results remained true irregardless of the participant's coronavirus exposure in their specific workplace setting.
"The mechanism underlying these associations remains unclear, but it has been hypothesised lack of sleep and sleep disorders may adversely influence the immune system by increasing pro-inflammatory cytokines and histamines," wrote the scientists.
Widespread inflammation that damages tissues has been linked to severe coronavirus complications.
Previous research has associated burn-out with diabetes, heart disease and even a premature death.
"These studies have suggested burn-out may directly or indirectly predict illnesses by occupational stress impairing the immune system and changing cortisol levels," wrote the scientists.
The team concluded: "We found lack of sleep at night, severe sleep problems and high level of burn-out may be risk factors for COVID-19 [the disease caused by the coronavirus] in frontline [healthcare workers].
"Our results highlight the importance of healthcare professionals' well-being during the pandemic."
In January 2021, scientists from King's College London reported nearly half of intensive care unit staff "met the threshold" for severe depression or anxiety, post-traumatic stress disorder or problem drinking.
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The scientists stressed their study is observational, and therefore does not prove cause and effect.
Coronavirus exposure, sleep issues and infection severity may also have been misremembered by the participants, they added.
Nevertheless, Dr Minha Rajput-Ray, from the NNEdPro Global Centre for Nutrition & Health, 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.
"From an occupational and lifestyle medicine perspective, 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."