An Israeli study has found that women living in areas with the worst light pollution have a 73% greater incidence of breast cancer than women from areas with the least night lighting.
I suppose it could be explained away by noting that light pollution is found in urban areas where people are exposed to more pollution and contaminants than rural dwellers except that an earlier study found the same thing in women working the night shift in hospitals. From the Environmental News Network:
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.