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).
In the lab, scientists at the Petrov Research Institute of Oncology in St. Petersburg, Russia, along with U.S. and German collaborators, subjected 50 female mice to alternating 12-hour periods of light and dark and exposed 50 similar mice to constant light. Of the latter group, 17 developed lung or liver tumors or leukemia, the researchers report in the Sept. 10 International Journal of Cancer. Just one mouse in the light-dark group developed any of these cancers, which are not known to be estrogen linked. The team observed no difference in the two groups’ rates of breast cancer or other cancers.
The mice exposed to constant light also experienced more irregular fertility cycles and ate less than the mice that got some darkness each day. Individuals in the two groups gained weight at the same rate.