Data from mice subjected to constant illumination suggest that artificial light may increase risks of lung and liver cancers and leukemia.
Exposure to light at night reduces production of melatonin, a hormone that calibrates the body's biological clock and its secretion of estrogen (SN: 10/17/98, p. 248: http://www.sciencenews.org/pages/sn_arc98/10_17_98/19981017fob.asp). The latter effect may explain why working the graveyard shift appears to increase a woman's risk of breast cancer and possibly other cancers associated with estrogen (SN: 11/17/01, p. 317: Available to subscribers at Cancer risk linked to night shifts).
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