Impacts of serum Vitamin D levels on sleep and daytime sleepiness according to working conditions

Abstract

Study Objectives: Low serum Vitamin D levels are known to be associated with working conditions and poor sleep, but precedent studies on this issue were limited by the absence of objective sleep measurements or clear distinction between daytime and night shift work. Hence, we aimed to examine serum Vitamin D levels and sleep in daytime and night-shift workers using actigraphy. Methods: A total of 412 night-shift and 432 daytime workers at Seoul National University Bundang Hospital was recruited. All participants completed questionnaires regarding demographic and clinical characteristics. They underwent blood tests for serumVitamin D levels. Objective sleep data were obtained from 150 night-shift workers and 203 daytime workers using actigraphy. Results: There was no significant difference in serum Vitamin D levels between night-shift and daytime workers after controlling for possible confounders. In daytime workers, Vitamin D deficiency was closely related to shorter duration of total sleep time (odds ratio [OR]: 3.07, 95% confidence interval [CI]: 1.51-6.26, P = .002) and higher risk of excessive daytime sleepiness (OR: 2.20, 95% CI: 1.30-3.74, P = .003). Deficient Vitamin D was also associated with life quality impairment regarding psychological health (OR: 1.83, 95% CI: 1.07-3.29, P =.028) and social relationship (OR: 1.78, 95% CI: 1.10-2.88, P =.020). However, in night-shift workers, no significant association was observed between serum Vitamin D level and sleep parameters, depressive/anxiety symptoms, or quality of life. Conclusions: Themodest adverse impact of poor vitaminDstatus on sleep could be attenuated by substantial shift work-related sleep disturbances in night-shift workers. Further studies might be needed to clarify the beneficial effect of Vitamin D supplementation for improving sleep and daytime sleepiness in workers with various working conditions.