Abstract
While the importance of the circadian system to health and well-being is extensively studied, the role of daylight exposure in these interactions is relatively poorly understood. Here we show, using a diurnal animal model naturally exposed to daylight, that daily morning exposure to 3000 lux, full spectrum electric light has beneficial health effects. Compared with controls, sand rats (Psammomys obesus) subjected to morning light treatment demonstrate daily rhythms with high peak to trough difference in activity, blood glucose levels and per2 gene expression in the suprachiasmatic nucleus, pre-frontal cortex, kidney and liver. The treated animals were also healthier, being normoglycemic, having higher glucose tolerance, lower body and heart weight and lower anxiety- and depression-like behavior. Our results suggest that exposure to high intensity light is important for the proper function of the circadian system and well-being, and are important in face of human's low exposure to daylight and extensive use of artificial light at night.
Highlights
While the importance of the circadian system to health and well-being is extensively studied, the role of daylight exposure in these interactions is relatively poorly understood
Blood glucose levels were significantly influenced by both photoperiod length and bright light treatment at both baseline and 120 min after glucose administration in the oral glucose tolerance test
We found that exposing diurnal sand rats to 1 h of BLT in the morning has a significant, beneficial effect on daily rhythms, blood glucose levels, glucose tolerance, body mass and depressive like behavior, and a near significant effect on the development of cataract
Summary
While the importance of the circadian system to health and well-being is extensively studied, the role of daylight exposure in these interactions is relatively poorly understood. In the laboratory, when sand rats are fed standard rodent food, they develop T2DM characterized by enhanced insulin secretion and insulin resistance at the early stages and insulin deficiency at an advanced stage[34,35] Under these conditions, they show a small peak-trough difference (PTD) in rhythmicity of activity, physiology and gene expression, and display depressive- and anxiety-like b ehaviors[17,33,36]. Our hypothesis that the comorbidity between T2DM, cardiac hypertrophy, depression-and anxiety-like behavior, that we have found in sand rats, is linked to disturbance in circadian rhythms, and fourth, that our finding that when kept outdoors sand rats show robust daily rhythms and do not develop the circadian syndrome may result from the exposure to high intensity, full spectrum natural light during the morning
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