Bright nights kindle cancers in mice.Data from mice subjected to constant illumination suggest that artificial light may increase risks of lung and liver cancers Liver Cancer Definition Liver cancer is a relatively rare form of cancer but has a high mortality rate. Liver cancers can be classified into two types. and leukemia leukemia (l  kē`mēə), cancerous disorder of the blood-forming tissues (bone marrow, lymphatics, liver, spleen) characterized by excessive production of immature or mature . Exposure to light at night reduces production of melatonin melatonin: see pineal gland. melatonin Hormone secreted by the pineal gland of most vertebrates. It appears to be important in regulating sleeping cycles; more is produced at night, and test subjects injected with it become sleepy. , a hormone that calibrates the body's biological clock and its secretion of estrogen (SN: 10/17/98, p. 248). The latter effect may explain why working the graveyard shift graveyard shift n. 1. A work shift that runs during the early morning hours, as from midnight to 8 a.m. 2. The workers on such a shift. Noun 1. appears to increase a woman's risk of breast cancer and possibly other cancers associated with estrogen (SN: 11/17/01, p. 317). 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 Hepatic tumors are tumors or growths on or in the liver (medical terms pertaining to the liver often start in hepato- or hepatic from the Greek word for liver, hepar). These growths can be benign or malignant (cancerous). 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. |
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