Beneficial effects of daytime high-intensity light exposure on daily rhythms, metabolic state and affect.

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.