Working the night shift may come with more than just fatigue—it could increase the risk of asthma in women, according to a new study that looked at health data from over 270,000 people in the UK. The findings, published in ERJ Open Research, suggest that women who regularly work night shifts are significantly more likely to develop moderate or severe asthma compared to those working traditional daytime hours. Interestingly, this trend was not observed in men. Researchers from the University of Manchester led the study, which focused on assessing the impact of shift work on asthma severity, with special attention to gender-based differences. The data included 274,541 working adults from the UK Biobank database.
Of these, 5.3 percent were diagnosed with asthma, and 1.9 percent were found to have moderate to severe forms of the condition. This severity was defined by the use of both an asthma-preventer inhaler and at least one additional treatment, such as oral steroids. Lead author Dr. Robert Maidstone explained that the study provides the first clear evidence of a link between night shift work and asthma severity in women.
“Asthma d i s p r o p o r t i o n a t e l y affects women. Women generally have more severe asthma, and a higher rate of hospitalisation and death from asthma compared to men,” said Dr. Maidstone. “We found that permanent nightshift workers had higher odds of moderate-severe asthma when compared to corresponding day workers.” Women who exclusively worked night shifts were found to be about 50 percent more likely to suffer from moderate or severe asthma than those working daytime hours. In contrast, the risk level among men remained relatively unchanged regardless of their work schedule.
While the study did not establish a direct cause-and-effect relationship, researchers proposed some biological mechanisms that could explain the gender disparity. One key factor may be the disruption of circadian rhythms, or the body’s natural internal clock, which is known to affect hormone levels and immune responses. The imbalance of sex hormones, in particular, may be contributing to the higher risk in women. Testosterone, for instance, has been shown to offer some protection against asthma. Since women naturally have lower levels of testosterone, this hormonal difference could partly explain their increased vulnerability.
Additionally, the kind of shift work that men and women typically perform may differ in environmental exposures or physical demands, which could also influence asthma risk. A particularly notable finding was observed among postmenopausal women. For those not on hormone replacement therapy (HRT), working night shifts was associated with nearly double the risk of developing moderate or severe asthma compared to their daytime counterparts. This suggests a potential protective role of hormones like estrogen in mitigating the effects of shift work on respiratory health. “Our results suggest that HRT might be protective against asthma for nightshift workers, however further research is needed to test this hypothesis in prospective studies and randomised controlled trials,” Dr. Maidstone added. Going forward, the research team plans to delve deeper into the biological basis of their findings. Their next steps involve examining whether sex hormones directly mediate the relationship between shift work and asthma, and whether targeted interventions like HRT could be considered as preventive measures for at-risk women.