Here’s yet another report linking cancer to nighttime lighting. A recent study approached the problem by overlaying a satellite map of the earth with maps of cancer registries throughout the world, and clear patterns emerged.

This confirms previous studies that have resulted in similar findings. A look at the health of those who work night shifts—nurses, flight attendants, emergency crews—found that women in these roles had cancer rates 60 percent higher than normal. Similar results were logged when mice were raised with 24/7 lights. And both of these studies took other factors, like differences in diet, into consideration.

And, as we’ve already noted, this has prompted the World Health Organization’s (WHO) International Agency for Research on Cancer to list night shift work as a probable human carcinogen, right up there with toxins like PVC (vinyl chloride) and PCBs (polychlorinated biphenyls).

The link, they say, is through melatonin, a hormone produced by the brain that helps to prevent the development of tumors. Our bodies produce this hormone at night, but have a more difficult time doing so when there is light present. Interestingly, women who are blind have lower rates of breast cancer, and so do mice injected with melatonin.

But women who work at night aren’t the only ones with higher than normal rates of breast cancer. People living in cities where there is a more strongly-lit nighttime environment also suffer from more cases of the deadly disease.

This is an alarming trend, indeed. For many of us who live in cities, getting away from the light is not as easy as it might seem. Covering the windows is one way, but I think I’ll be tempted to wear my night mask more from now on. Gotta keep that melatonin flowing!