A new study, published online in the journal Thorax, has found that shift workers, especially permanent night shift workers, are at a greater risk of developing moderate to severe asthma.

Researchers said the study findings are potentially “far-reaching” given the high prevalence of shift work and asthma in industrialized nations.

At least 1 in 5 workers in the developed nations works rotating or permanent night shifts.

Shift work can affect your circadian rhythm (internal body clock) with the external light and dark cycle. And this could increase the risk of various disorders, including diabetes, cardiovascular disease and cancer.

The researchers wanted to understand whether shift work is associated with an increased risk of asthma because the symptoms of asthma vary considerably according to the day and night time.

They also wanted to explore how influential chronotype, an individual’s body clock preference for a morning (‘lark’) or evening (‘owl’) activity, and genetic predisposition is related to asthma.

After considering the participants’ age, sex, and other potentially influential risk factors, the researchers found a 36% increase in the risk of having moderate to severe asthma in permanent night shift workers than those who worked normal office hours.

In addition, the risk of asthma-like symptoms such as wheeze or airway whistling was 11 to 18% higher among people who worked any of the three shift patterns, and the risk of poorer lung function was around 20% higher in rotational and permanent shift workers.

People who were either larks or owls, called “extreme chronotypes,” were more likely to have asthma even after considering their potentially influential risk factors.

Furthermore, the risk of moderate to severe asthma was 55% higher among larks working irregular shifts, including night shifts.

However, genetic predisposition to asthma did not affect the risk of developing asthma among those working rotational shifts.

The researchers cautioned that this is an observational study so it cannot establish the cause and the effect; however, they added, “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,” the authors explained.

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

Worldwide, asthma affects nearly 340 million people and it costs a great deal of health care services in the United States.

“There are no specific national clinical guidelines for how to manage asthma in shift workers,” the investigators highlighted, “but adapting shift work schedules to suit individual chronotype might be a worthwhile public health measure that is worth exploring further.” The article originally appeared on Science Daily.