Invited Speaker

Light as a Drug: Circadian Disruption, Melatonin Suppression and Cancer
Russel J. Reiter
USA

The use of artificial light after darkness onset and the widespread use of security lights at night have corrupted the photoperiodic environment. A regular light: dark cycle is required for the regulation of circadian rhythms including the melatonin cycle. Melatonin, an indoleamine produced exclusively in and released from the pineal gland at night, is an important synchronizer of circadian rhythms and an anti-cancer agent. The amount of melatonin endogenously produced is proportional to the duration of the daily dark period. Due to the widespread use of artificial light, the amount of darkness humans witness is becoming progressively less creating a relative melatonin deficiency. Epidemiology studies have repeatedly shown that several cancer types, e.g., breast, prostate, colorectal, are on the increase in countries which use light excessively after darkness onset and in night shift workers. A working hypothesis is that light pollution depresses melatonin and predisposes humans to an elevated cancer risk. This is strongly supported by animal studies, in which melatonin readily inhibits many cancer types via multiple mechanisms. The combination of a relative melatonin deficiency and the marked circadian disturbances that occur due to the presence of light after darkness onset is believed to be detrimental to human health.