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Working in night shifts raises cancer risk8 December, 2007 Working in night shifts – dubbed as the “graveyard shift” – is likely to raise the risk of cancer. A team of 44 scientists from 10 countries, commissioned by the International Agency on Cancer Research of the World Health Organization (WHO), has found proof of a connection between cancer and the people working in night shifts. There is a higher rate of breast cancer in female nurses who work in night shifts, according to the report published in the December 2007 issue of medical journal The Lancet Oncology. The scientists reviewed studies in which animals were exposed to light at night, which disrupted the animals’ circadian rhythm – or, the body’s biological clock, the regular changes in mental and physical characteristics that occur in the course of a day. They found adequate evidence of a connection between the disruption of circadian rhythm and cancer. Kurt Straif, who works for the International Agency for Research on Cancer in France, wrote in the report: “Shift work that involves circadian rhythm disruption is probably carcinogenic to humans.” It is believed that work in night shift might raise the risk of cancer by suppressing production of melatonin, a hormone chemical involved in the circadian rhythm. Melatonin, which can suppress development of tumour, is normally produced at night. In January 2008, the International Agency for Research on Cancer (IARC), the cancer arm of the World Health Organisation, will add ‘overnight shift work’ as a probable carcinogen. The American Cancer Society is likely to follow suit. Till now, the American Cancer Society has considered the link between work and cancer to be “uncertain, controversial or unproven.” Experts estimate that nearly 20% of the working population in developed countries works in night shifts. Richard Stevens, a cancer epidemiologist and professor at the University of Connecticut Health Centre, the United States, was among the first to spot the connection between night shift and cancer. In 1987, Richard Stevens published a paper suggesting a link between light at night and breast cancer. Stevens was trying to make out why incidence of breast cancer suddenly shot up starting in the 1930s in industrialized societies, where nighttime work was considered a characteristic of progress. Several studies conducted in recent years have found that women working at night over many years were more prone to breast cancer than those who did not. Also, animals that have their light-dark schedules switched were found to develop more cancerous tumors and die earlier. Some research has also suggested that men working at night may have a higher rate of prostate cancer. Another factor that may cause cancer is sleep deprivation as people who work at night are not able to reverse their day-and-night cycles completely. According to Mark Rea, director of the Light Research Center at Rensselaer Polytechnic Institute in New York, “night-shift people tend to be day-shift people who are trying to stay awake at night.” Not getting enough sleep makes one’s immune system vulnerable to attack, and less able to ward off potentially cancerous cells.
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