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Mar 272009

By Carol Sonenklar
Green Right Now

During a power outage in California in the 1990s, alarmed residents reportedly called in to report a strange, cloudy shape in the nighttime sky. It turned out to be the Milky Way- seen for the first time. For those of us who live in urban or suburban areas, an overabundance of artificial nighttime light, or light pollution, is nothing new. But light pollution isn’t just a bane to astronomers and an annoyance to the rest of us: studies show that it also poses real health risks, including some increased rates of cancer.

A recent study done in Israel headed by Richard Stevens, a professor and cancer epidemiologist at the University of Connecticut Health Center, and published in Chronobiology International, has shown some disturbing trends between women exposed to large amounts of artificial night light and breast cancer.

Stevens’ team overlaid satellite photos to measure nighttime artificial light levels with a map detailing the distribution of breast cancer cases. Those women living in the brightest areas (as defined by being able to read at outdoors at midnight) had a 73% higher risk of developing breast cancer than those living in areas with the least outdoor lighting.

These results correlate with an earlier study done in 2005 that showed women who worked night shifts in hospitals also had higher incidences of breast cancer. The report, published in Cancer Research, suggests that melatonin-or rather the lack of it-may be the cause. Melatonin is an essential hormone that our bodies make at night while we sleep. It requires darkness and plays a critical role in regulating our internal clocks. For women, the light-sensitive hormone is particularly important since scientists suspect that melatonin helps to reduce estrogen levels–higher estrogen levels being a factor in developing breast cancer. And melatonin levels drop precipitously in the presence of artificial light.

This research helps to explain two stark facts that epidemiologists have long known: breast cancer rates are three to five times higher in industrialized countries and, that breast cancer rates are 20 to 50 percent less in blind women.

Furthermore, a study released in February by University of Haifa researchers, found elevated risks of prostate cancer in countries with the highest levels of artificial light.