Danish government's decision to compensate breast cancer stirs debate

Are employees who work the late shift at a greater risk for developing cancer? They might be, according to a decision by government officials in Denmark, and if so, they are entitled to compensation.

The Danish government's National Board of Industrial Injuries awarded 37 female employees workers' compensation benefits after they alleged that they developed breast cancer as a result of their many years of working the night shift. Despite previous research that has tied working the late shift to an increase in sleep disorders and other medical conditions, health and safety officials have debated whether these working conditions can lead to a greater risk of cancer. Demark officials said they based their decision on a range of international studies that have concluded that late-night exposure to light may diminish levels of a natural cancer fighting hormone. One such study, published in 2001 by the Fred Hutchinson Cancer Research Center, concluded that employees who work the night shift could increase their risk of breast cancer by as much as 60 percent.

Effect on U.S. employers. It may be too early to tell if Denmark's decision will lead to changes in the United States, but a professor at Tulane University believes the link between late-night work and increased cancer risks exists. Dr. David Blask, professor in the School of Medicine's Department of Structural and Cellular Biology, is an expert on cancer biology, circadian rhythms, and the health implications of exposure to light. In the early 1980s, Blask was one of only a handful of scientists studying regulation of breast cancer development and growth by melatonin, a hormone produced by the pineal gland during sleep in the darkness of night. Melatonin modulates many of the body's natural circadian rhythms, including the sleep/wake cycle, and has been shown to have important anticancer properties.

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Blask said shift workers have been shown to have higher risks of breast, prostate and other cancers. Using specially designed photoperiodic chambers, which allow precise control over light exposure at night, he and his research team have demonstrated that manipulating light intensity at night, and thus melatonin production, dramatically affects human breast cancer growing in rats. The experiments, he said, show that reduced levels of melatonin coupled with higher levels of light at night boosted human breast cancer tumor growth in rats.

However, not all researchers agree. According to a 2007 study by The Ohio State University, researchers found no link between working the night shift and the risk of developing any kind of cancer. They came to this conclusion after analyzing nearly 20 years worth of data that compared people who had jobs that required working during the day to those who had jobs that required night-shift work. The researchers, however, concluded more studies are necessary because the "effects of melatonin on cancer development in humans are not well understood."

June 11, 2009

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