ONE IN FIVE European workers could be at increased risk of cancer because they work shifts, an international panel of experts has found. According to the International Agency on Cancer (IARC), shiftwork that disrupts circadian rhythms--the so-called body clock--is "probably carcinogenic to humans". Experts from 10 countries gathered at IARC in October 2007 to examine the scientific evidence on Dancer and shiftwork--the first time the group has discussed the issue--and decided that shiftwork probably causes cancer in humans. Among the evidence IARC evaluated were eight epidemiological studies on cancer in shiftworkers from several countries. Six out of these eight studies found a "modestly increased risk of breast cancer" in long-term shiftworkers. The evidence from animal studies was stronger. In the 20-plus animal studies IARC looked at, most found major increases in cancer in rodents that were exposed either to constant light, dim light at night or simulated jet lag.
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