Impact of light therapy on rotating night shift workers: the EuRhythDia study

AIMS: Disturbances in circadian rhythms may promote cardiometabolic disorders in rotating night shift workers (r-NSWs). We hypothesized that timed light therapy might reverse disrupted circadian rhythms and glucose intolerance observed among r-NSWs). METHODS: R-NSWs were randomly assigned to a protocol that included 12 weeks on followed by 12 weeks off light therapy (n = 13; 6 men; mean age, 39.5 ± 7.3 years) or a no-treatment control group (n = 9; 3 men; mean age 41.7 ± 6.3 years). Experimental and control participants underwent identical metabolic evaluations that included anthropometric, metabolic (including oral glucose tolerance tests), lipid, and inflammation-associated parameters together with an assessment of sleep quality and expression of circadian transcription factors REV-ERBα and BMAL1 in peripheral blood mononuclear cells (PBMCs) at baseline, 12 weeks, and 24 weeks of the protocol. RESULTS: Twelve weeks of warm white-light exposure (10,000 lx at 35 cm for 30 min per day) had no impact on sleep, metabolic, or inflammation-associated parameters among r-NSWs in the experimental group. However, our findings revealed significant decreases in REV-ERBα gene expression (p = 0.048) and increases in the REV-ERBα/BMAL1 ratio (p = 0.040) compared to baseline in PBMCs isolated from this cohort. Diminished expression of REV-ERBα persisted, although the REV-ERBα/BMAL1 ratio returned to baseline levels after the subsequent 12-day wash-out period. CONCLUSIONS: Our results revealed that intermittent light therapy had no impact on inflammatory parameters or glucose tolerance in a defined cohort of r-NSWs. However, significant changes in the expression of circadian clock genes were detected in PBMCs of these subjects undergoing light therapy.