[Light, melatonin and internal cancers - recent facts and research perspectives]

Visible light of sufficient intensity inhibits melatonin biosynthesis and numerous experimental studies suggest that melatonin may protect against cancer. From a public health point of view it is important to verify or falsify the hypothesis that artificial light - or even sunlight itself - suppresses melatonin production sufficiently to increase the risk of developing cancers of internal organs. Since humans are exposed universally, even small risk elevations could lead to numerous cases. Recent epidemiological studies of people exposed to anthropogenic light-at-night in the course of shift work and first evaluations of natural light experiments in blind people and in residents of the Arctic are compatible with the possibility that light can influence - at least hormone- dependent - cancer developments via melatonin. To systematically investigate the effect of geographically different light intensities on melatonin production in man, a pan-European study is suggested. Further epidemiological investigations can contribute to the understanding of the patho-physiological relationships between light, melatonin and human biology.