Impact of artificial light at night and night shift work on brain functions and metabolism

The present review focusses on artificial light at night (ALAN) and night shift work (NSW) as examples for chronodisruption occurring in modern societies. Chronodisruption can lead to significant sleep and health problems and increase the risk of chronic diseases. This pathomechanism involves endocrine systems (glucocorticoids, melatonin). ALAN affects at least 80% of mankind and disturbs physiological, biological and behavioral processes in wildlife. In humans, the nighttime use of illuminated screens contributes to ALAN, with as yet unforeseeable consequences for body and brain. Acute continuous light exposure triggers pro-inflammatory responses in the brain which may make it more vulnerable to additional aversive stimuli. Moreover, acute continuous light impairs cognitive function and synaptic plasticity and leads to an increase in corticosterone, a stress hormone and an important mediator in the circadian system. Several studies on NSW reported increased risk for sleep disorders, cancer, cardiovascular disease, type 2 diabetes, obesity, and depression. However, objective imaging analyses supplemented by neuropsychological examinations revealed that NSW has only minor effects on brain functions. Moreover, a recent study showed that NSW was not accompanied by metabolic, cardiovascular or immunological problems. In conclusion, ALAN may be considered a relevant factor influencing human health and biodiversity and should be avoided whenever possible. Studies on the effects of NSW report varying results. This may be due to differences in light intensity during shift, the quality of the occupational health service and the shift work schedule. All these aspects need further investigations to prevent or mitigate the health risk of NSW.