Circadian rhythms are patterns of behaviour, physiology, and metabolism that occur within a period of approximately 24 h. The higher risk of breast and prostate cancers among shift workers, as well as the general population, are reported to be associated with circadian rhythm disruption caused by exposure to light at night. We focused on the effects of bright light before bed comparing effects between men and women.
Male and female healthy volunteers aged 20–30 were exposed to 4 hours of bright light before bed for 3 and 4 days.
We analyzed the shift of circadian rhythms of subjects based on cortisol secretion patterns in response to short periods of bright-light exposure at bedtime. We also found an increase of oxidative stress including MDA, 8-OHdG, and total antioxidants in both male and female volunteers.
These results suggest that bright light exposure before sleep, often encounter in modern daily life, has a considerable influence on the human body. The chronic effects of light exposure before bed time such as the carcinogenic effects caused by circadian disruption and oxidative stress need further investigation.