Asthma risk for permanent night shift workers

Shift workers, particularly those who work nights permanently, could be at increased risk of developing moderate to severe asthma, researchers say today.

The researchers behind the observational study, in Thorax, say their findings potentially have “far-reaching” public health implications

About one in five employees in the developed world works permanent or rotating night shifts, which can cause a person’s circadian rhythm to be out of step with the external light and dark cycle and is associated with a greater risk of various metabolic disorders, cardiovascular disease, and cancer.

Because asthma symptoms vary according to the time of day or night, the researchers wanted to establish if shift work was also associated with an increased risk of asthma and/or its severity and to see how influential chronotype and genetic predisposition to asthma is.

The researchers, from the UK and the USA, used data from the UK Biobank, drawing on medical, lifestyle, and employment information supplied between 2007 and 2010 by 286,825 participants.

All were aged between 37 and 72 and were either in paid employment or were self-employed. Of these, 83% worked regular office hours, while 17% worked shifts, 51% of whom included night shifts.

Shift workers were more likely to be men, smokers, and to live in urban areas and in more deprived neighbourhoods. They also drank less alcohol, slept fewer hours, and worked longer hours.

Night shift workers were more likely to have poorer health and work in service jobs or as process, plant and machine operatives.

About 5% (14,238) of all the participants had asthma, of whom 4783 reported moderate-to-severe symptoms.

The researchers compared the effect of working office hours with shift work on asthma diagnosis, lung function, and symptoms of asthma and found that permanent night shift workers had a 36% increased risk of having moderate to severe asthma compared to those working normal office hours.

The odds of wheeze or airway whistling were 11-18% higher among those working any of the three shift patterns, while the odds of poorer lung function were around 20% higher in shift workers who never or rarely worked nights and in those working permanent night shifts.

People classed as extreme chronotypes were significantly more likely to have asthma, with the odds of moderate to severe asthma being 55% higher among larks working irregular shifts.

Although this is an observational study, the researchers say that it is plausible that circadian misalignment leads to asthma development.

“Interestingly, chronotype does change with age, getting later through adolescence and then earlier as adults age, suggesting that older individuals might find it more difficult to adjust to night shift work than younger adults,” they write.

“The public health implications of our findings are potentially far-reaching, since both shift work and asthma are common in the industrialised world.”

Night shift work is associated with an increased risk of asthma Thorax 17 November 2020; doi: 10.1136/thoraxjnl-2020-215218

[abstract]

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