Another Breast Cancer Risk Factor? Artificial Light at Night? Pull the Shades!

PJ Hamel Health Guide
  • A recent article in The Washington Post highlighted a just-published article in Chronobiology International, a journal for researchers who study the relationship between time and biological processes, e.g., why we fall asleep at night and wake up in the morning. Talk about niche: this isn’t a magazine you’re likely to see while standing in the checkout line at the supermarket. But the most recent issue includes the results of a fascinating study conducted by researchers at the University of Haifa, in Israel. And this study adds to the growing body of evidence that light—yes, light, of all things—may be a significant breast cancer risk.

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    OK, before you start rolling your eyes, this isn’t as weird as it sounds. We’re talking artificial light: especially fluorescent light, though incandescent bulbs are being implicated, too. And we’re talking only at night, when we’d generally be sleeping. Researchers have known for years that breast cancer rates are 60% above normal for nurses, flight attendants, women who work the third shift, and others working through the night. And in December, a unit of the World Health Organization announced that shift work is now officially classified as a “probable carcinogen,” putting it in the same category as toxic chemicals such as PCBs. 

    “Whew,” you’re saying. “I don’t work the night shift, guess this doesn’t apply to me.” Not so fast. This is where that new Israeli study comes in. Scientists overlaid satellite photos, taken of the earth at night, with cancer registries. And there’s a specific correlation between areas with the brightest and most night lighting—i.e., urban areas—and an increased incidence of breast cancer. In fact, the incidence of breast cancer is about 73% higher in areas with the most and brightest lights, as opposed to those with the least. 

    What’s going on here? Melatonin, a hormone that suppresses tumor development, is produced by your body at night, in the dark. The presence of light dramatically slows the production of melatonin. Less melatonin, less tumor suppression, more risk of cancer, particularly breast cancer. Researchers have regularly produced these results in the lab, with their white mice. Now they’re seeing real-world evidence that it’s not just mice in brightly lit cages who are more likely to get cancer: it’s us.

    Let’s bring this down another level. You live in a typical suburb, with well-lit streets. There’s a streetlight that shines into your bedroom, casting shadows on the wall at night. Or try this: you lie down in your child’s bed to help her go to sleep. She’s got the light on, scared of the monsters under the bed. You fall asleep, and you both slumber for several hours, in her brightly lit bedroom. Or this: your computer is on your desk, in a corner of the bedroom; its screen glows all night, because you figure it takes more power to turn it off than to simply leave it on screen-saver. Are all of these random, everyday occurrences increasing your breast cancer risk?

  • Maybe so. Abraham Haim, an Israeli scientist, questions the use of energy-saving fluorescent bulbs, which suppress melatonin more than old-fashioned incandescent lights. “This may be a disaster in another 20 years, and you won’t be able to reverse what we did by mistake,” said Haim in the Post, speaking about the push for energy-efficient lighting.

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    So, what? We dine by candlelight and go to bed at 8 p.m.? No, of course not. But it might be sensible to ensure adequate levels of melatonin by giving yourself a regular break from light—ALL light. When you go to bed, hit that light switch and turn off the computer. Pull the shades in your bedroom. Don’t fall asleep in front of the TV. And if it’s impossible to find someplace dark to sleep, wear eyeshades. Remember, all those years ago, your mom yelling up the stairs for you to turn off the light and go to sleep? She was right. 

Published On: April 20, 2008