Exposure to excessive artificial light at night may be disrupting the body's natural melatonin balance and raising the incidence of some cancers, American researchers have proposed. Professor George Brainard, a neuroscientist at Philadelphia's Thomas Jefferson University, reported early results of his research at the annual meeting of the American Association for the Advancement of Science in Denver, USA. He also announced the discovery of what appears to be a novel 'photoreceptor system' in the human eye that regulates the biological and behavioural effects of light on the body. His team has established that specific wavelengths control the production of melatonin, with the blue region of the visible spectrum being the most potent. He said that a growing body of research suggests that too much exposure to light at night can interrupt the body's production of melatonin, which has been shown in the laboratory to inhibit the growth of some types of cancer cells. Light-induced melatonin suppression has also been shown to increase tumour growth in animal models. Melatonin is produced by the pineal gland in the brain, and is an essential part of the system that controls the body's circadian (or day-night) rhythm. The eye uses the presence of light to regulate the production of melatonin; the body then produces high levels of melatonin at night, and low levels during the day. The increased and unnatural levels of light we are exposed to in the modern world after dark (and the ensuing disruption in the production of melatonin) may be raising the risk - as well as the incidence - of cancers such as breast cancer, argued Brainard.
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