Norwegian nurses working night shifts are significantly more likely to report common infections, with sleep debt emerging as a key contributing factor, according to new research published in the journal Chronobiology International. The large-scale study surveyed over 1,300 nurses and found that those who had accumulated sleep debt were more vulnerable to illnesses such as the common cold, sinusitis, and gastrointestinal infections.

The study found a clear dose-dependent pattern: nurses with more than two hours of sleep debt were more than twice as likely to suffer from several types of infections compared to those who reported no sleep debt. While nearly 74% of the nurses surveyed had reported at least one infection in the past three months, the strongest associations were tied to common colds and digestive illnesses.

Researchers drew upon data from the long-running Survey of Shift Work, Sleep, and Health (SUSSH), focusing on responses collected in 2018. They examined how shift patterns, night work, and sleep habits influenced infection rates among a sample largely composed of women in their early forties. Participants were asked about their typical sleep duration, how much rest they needed to feel recovered, and whether they had experienced specific infections recently.

Despite previous research linking short sleep to poor health outcomes, this study did not find a significant association between sleep duration alone and increased infections. Instead, the difference appeared when looking at the discrepancy between how much sleep nurses felt they needed and how much they actually got. Nurses who reported a gap of over two hours between needed and actual sleep were particularly at risk.

Night work on its own was also associated with a higher incidence of the common cold. Nurses who worked between one and 20 night shifts in the previous year had an increased likelihood of reporting a cold, but there was no clear escalating trend with more night shifts beyond that. The study did not find any association between night work and other infections such as pneumonia or urinary tract infections.

Another focus of the study was on “quick returns” – work schedules where the rest period between two shifts is less than 11 hours. Although these schedules have previously been linked to fatigue and disrupted sleep, the researchers found no evidence that quick returns led to more frequent infections.

The findings raise concerns about the health consequences of shift work, particularly in professions like nursing that require round-the-clock coverage. While sleep duration remains important, the study suggests that how rested individuals feel based on their personal sleep needs could be a more meaningful indicator of immune health.

The study’s authors noted that the data collection took place in the spring, outside of the usual flu season, which could mean that infection rates were actually underrepresented. They also acknowledged limitations including the reliance on self-reported data and the homogeneity of the sample, which was mostly female and based in Norway. Even so, the study adds weight to growing evidence that irregular work schedules and insufficient sleep can compromise health, particularly in demanding healthcare roles.