From the Archive: What happens when lights at night mess with our circadian rhythms — and health.
At 4:31 a.m. on Jan. 17, 1994, residents of Los Angeles were jolted awake by a 6.7-magnitude earthquake that killed more than 60 people, crumpled buildings and freeways, swallowed automobiles, ignited fires and caused a blackout. That last effect, plunging the city into darkness, prompted dozens of residents to call the city’s Griffith Observatory because of something weird they saw in the night sky: the Milky Way.
That’s the working hypothesis of researchers studying the purported effects of what they call Artificial Light at Night, or ALAN. It’s not the what of light that promotes diseases, they say, but the. Exposing the retina to light at night messes with your body’s circadian rhythm, the beat of life estimated to have evolved 2.5 billion years ago in response to Earth’s 24-hour rotation.
Similar links between outdoor lighting and the rate of breast cancer diagnosis have been observed in the state of Georgia, and indeed around the world. An association in cancer rates — in this case, prostate cancer — was reported this March by researchers in Israel. In a 2005 study, he described what happened when he took melatonin-depleted blood from premenopausal women who had been exposed to light at night and infused it through human breast cancer xenografts in nude rats. The cancer, he found, grew faster.
“If you’re living in an area with more street light, you’re likely to have more of a night life,” she says. “You probably stay up later, eat later, drink later. That doesn’t mean that the streetlight itself is causing cancer.”