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

Abstract

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.

Circadian desynchrony and glucose metabolism

“…In diurnal sand rats, daily morning exposure to high‐intensity full‐spectrum light (3000 lux), had beneficial effects on glucose tolerance, compared to neutral light exposure (800 lux) 168 . In human shift workers, a randomized‐controlled trial ( n = 24) investigating the effect of 12 weeks of daily 50‐min light therapy (10 000 lux) found reductions in post‐OGTT glucose, 169 while in another randomized‐controlled trial ( n = 12), no differences in glucose tolerance were detected after 12 weeks of daily 10 000 lux light therapy 170 . Another randomized‐controlled trial in insulin‐resistant individuals found that bright light during the day (1250 lux) in combination with dim light in the evening (5 lux) lowered predinner glucose levels and increased night‐time metabolic rate.…”

“…168 In human shift workers, a randomizedcontrolled trial (n = 24) investigating the effect of 12 weeks of daily 50-min light therapy (10 000 lux) found reductions in post-OGTT glucose, 169 while in another randomized-controlled trial (n = 12), no differences in glucose tolerance were detected after 12 weeks of daily 10 000 lux light therapy. 170 Another randomizedcontrolled trial in insulin-resistant individuals found that bright light during the day (1250 lux) in combination with dim light in the evening (5 lux) lowered predinner glucose levels and increased night-time metabolic rate. In addition, postprandial glucose levels were lower when dinner was consumed during bright light, again emphasizing that indoor light intensity modulates postprandial glucose uptake.…”

Circadian rhythm disruption and endocrine-related tumors

“…In addition, a three-meal diet with a rich carbohydrate breakfast appears to optimize HbA1c, reduce body weight and insulin requirements, and concomitantly upregulate the expression of CGs in patients with T2DM compared to a six-meal isocaloric diet[ 45 ]. Moreover, a 12-wk warm light exposure can alter the expression of REV-ERBα in shift workers[ 46 ], suggesting that light therapy could be used to rectify circadian disturbances. Based on current data, future research could uncover therapeutic methods for metabolic disorders based on circadian rhythms.…”

Circadian Dysfunction in Adipose Tissue: Chronotherapy in Metabolic Diseases

“…Light therapy, which involves exposing patients to bright light in the early morning for several days, is thought to work by entraining the sleep–wake cycle by ocular stimulation of the suprachiasmatic nucleus and is expected to alleviate sleep disturbances and improve circadian rhythmicity [ 240 , 241 ]. However, in some clinical studies, light therapy was not found to be superior regarding insulin sensitivity, glucose tolerance, and inflammatory parameters, although the peripheral blood mononuclear cells of patients under light therapy showed a significant alteration in the circadian clock gene expressions [ 241 , 242 ].…”