This studied the association between duration of night shift exposure and mortality in a large sample, controlling for lifestyle factors and age & stratifying by age & occupational group.
First, authors note that previous work has demonstrated associations between shift work involving night work & higher risk of ischemic heart disease, diabetes, occupational incidents & breast cancer. Further, exposure to night work at a young age has also been associated with multiple sclerosis & rheumatic arthritis risk.
Nevertheless, they note that despite research around morbidity & shift work – mortality has been studied to a limited extent.
Data came from twins that participated in Screening Across the Lifespan Twin (SALT) study, where data was collected at two points separated by 18 years. Data encompassed >42k individuals, with 30% having been exposed to night work. A twin approach was used to help analyse shared family & genetic factors.
Results:
Overall, the hazard ratio (HR) for all-cause mortality for any night work over the career (1 – 45 yrs of night work) was modest at HR 1.07, compared to people who never worked night.
However, this rose to HR 1.15 for longer exposure to night work (>5 yrs).
When looking at specific-cause mortality, mortality risk increased to HR 1.25 for circulatory disease with night exposure > 5 years, and 1.16 for mortality due to cancer.
Regarding occupation type and mortality risk, blue collar work (BCW) wasn’t found to be statistically significant, whereas long exposure for white collar work (WCW) was significant (HR 1.20) for elevated mortality risk.
With gender, male WCW was significantly associated with mortality >5 years of night work (HR 1.28), but not for BCW.
Hereditary factors didn’t influence results significantly.
Overall, the authors conclude that longer duration (>5 yrs) night work is associated with elevated mortality risk but that apart from this, there appears to be no clear dose-response pattern. That is, this study found more of a threshold where risk suddenly increased, rather than an accumulation.
Also, while an increased risk for female WCW was observed over long periods – it wasn’t found to be statistically significant. But, other work by the same authors did find a significant association for female WCW.
Authors: Åkerstedt, T., Narusyte, J., & Svedberg, P. (2020). Scandinavian Journal of Work, Environment & Health, 46(5), 508.
Study link: https://doi.org/10.5271/sjweh.3892
Link to the LinkedIn article: https://www.linkedin.com/pulse/night-work-mortality-link-occupational-group-sex-ben-hutchinson
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