The importance of light and darkness in the development of the circadian rhythm

Department of Human Physiology and Biophysics, Nicolae Testemitanu State University of Medicine and Pharmacy, Chisinau, Republic of Moldova, The 8th International Medical Congress for Students and Young Doctors, September 24-26, 2020Introduction. Currently, in the world, nights are extremely illuminated, whereas during daytime people are exposed to dim light conditions. Exposure to artificial light at night results in a disruption of the circadian system and melatonin suppression associated with an increased prevalence of numerous diseases. Aim of the study. The aim of this review was to assess the current information regarding the influence of light and dark on the secretion of human melatonin. Materials and methods. A broad English search was undertaken of the PubMed and Scopus database for the terms ”melatonin suppression”,”melatonin and light”, articles from 2010-2020 were selected. Results. Studies have shown that light-induced nocturnal melatonin suppression may be affected by intensity (350-1000 lx was sufficient to significantly suppress melatonin levels), wavelength (459 nm to 484 nm ), time of exposure (5 seconds-6,5 h), temperature (6500k induced greater suppression). Appropriately timed light exposure has been shown to phaseshift human circadian rhythms. More prolonged exposure to light during the day (summer, bright environment) might reduce melatonin suppression at night, blue light having a more acute preventive impact. Light influences melatonin's functions, increasing the risk for diabetes type 2, heart disease, obesity, some types of cancer, depression, bipolar disorders. Conclusions. Further research assessing the impact of light on melatonin secretion should be undertaken considering the following factors: alcohol consumption, age, eye color, posture, phase of the menstrual cycle, administration of oral contraceptives, physical exercise, pupil size, sleep pattern and clearly indicating the details of the experimental protocol