Shift Work in Nurses: Contribution of Phenotypes and Genotypes to Adaptation

TLDR

Shift work misaligns sleep/wake, hormonal, and physiological cycles, increasing risks for cardiovascular, metabolic, gastrointestinal, cancer, and mental disorders, yet the roles of sleep timing, chronotype, and circadian clock gene variation in adaptation remain unclear. The study assessed 388 day‑ and night‑shift nurses using newly defined sleep strategies, chronotype, and polymorphisms in circadian clock genes (CLOCK, NPAS2, PER2, PER3). Night‑shift nurses who used sleep deprivation to transition between diurnal sleep and work days were the most poorly adapted, while chronotype and specific gene polymorphisms influenced adaptation outcomes such as alcohol/caffeine intake, sleepiness, and sleep phase, with many effects varying by shift type, underscoring that sleep strategy, chronotype, and genotype jointly shape circadian adaptation and have implications for health‑care policy.

Abstract

Background Daily cycles of sleep/wake, hormones, and physiological processes are often misaligned with behavioral patterns during shift work, leading to an increased risk of developing cardiovascular/metabolic/gastrointestinal disorders, some types of cancer, and mental disorders including depression and anxiety. It is unclear how sleep timing, chronotype, and circadian clock gene variation contribute to adaptation to shift work. Methods Newly defined sleep strategies, chronotype, and genotype for polymorphisms in circadian clock genes were assessed in 388 hospital day- and night-shift nurses. Results Night-shift nurses who used sleep deprivation as a means to switch to and from diurnal sleep on work days (∼25%) were the most poorly adapted to their work schedule. Chronotype also influenced efficacy of adaptation. In addition, polymorphisms in CLOCK, NPAS2, PER2, and PER3 were significantly associated with outcomes such as alcohol/caffeine consumption and sleepiness, as well as sleep phase, inertia and duration in both single- and multi-locus models. Many of these results were specific to shift type suggesting an interaction between genotype and environment (in this case, shift work). Conclusions Sleep strategy, chronotype, and genotype contribute to the adaptation of the circadian system to an environment that switches frequently and/or irregularly between different schedules of the light-dark cycle and social/workplace time. This study of shift work nurses illustrates how an environmental "stress" to the temporal organization of physiology and metabolism can have behavioral and health-related consequences. Because nurses are a key component of health care, these findings could have important implications for health-care policy.