Abstract 14384: Light Therapy Improves Circadian Blood Pressure Control and Glucose Homeostasis in Rotating Night Shift Workers via Mechanisms Independent of Melatonin

Abstract

Introduction: Night shift work is associated with high rates of hypertension, heart disease, and metabolic syndrome. These cardiometabolic diseases have been linked to the disruption of circadian rhythms in night shift workers. Rotating night shift work is increasingly common in the working population worldwide. Hypothesis: We hypothesized that light therapy might help to normalize disrupted circadian rhythms and stabilize diurnal control of blood pressure and glucose tolerance in rotating night shift workers. Methods: We randomized 24 rotating night shift workers (mean age, 36±13 years, 7 males) who had spent a median of 6 years on rotating night shifts with a median of 6 night shifts/month to 12 weeks of light therapy (light during first half of each night shift and in the morning of off-work days) or no intervention and compared them with 12 daytime workers (37±11 years, 6 males). We measured oral glucose tolerance (OGTT), 24h blood pressure and arterial stiffness, and the circadian profiles of melatonin, cortisol, metanephrine and normetanephrine at baseline, after 12 weeks of intervention, and 12 weeks after the end of intervention. Results: At baseline, fewer night shift workers showed dipper status of blood pressure as compared to daytime workers (21% vs. 55%; p<0.001). After 12 weeks of light therapy, there was a highly significant increase in the proportion of dippers (to 42%; p<0.0001). We also observed a significant decrease in serum glucose during OGTT in the light therapy group (-22%; p<0.05), with no change in serum insulin. Whilst circadian profiles of melatonin and cortisol were unchanged, there was a significant reduction in nighttime plasma metanephrine and normetanephrine levels in the light therapy group (p<0.01). Conclusions: Chronotherapeutic light therapy significantly improves diurnal blood pressure control and glucose tolerance in rotating night shift workers. This effect is unrelated to mechanisms traditionally linked to the circadian clock like melatonin and cortisol, but it is paralleled by reduced catecholamine levels. Our data suggest that chronotherapeutic light therapy may improve the adjustment to atypical working hours in rotating night shift workers, thereby reducing stress and improving cardiometabolic function.