Air and water pollution are pretty understandable health risks. But light pollution? It sounds a little hokey at first. Tons of streetlights and lit-up office buildings make Earth look freakishly nocturnal from space, sure, but could they actually make us sick?

Rebecca Boyle says yes. Those of us staring at our phones, laptops, and iPads until bedtime aren’t just inducing insomnia — we could be playing with “the major factor in depression, obesity, and cancer,” she writes in Aeon Magazine.

That’s because our bodies need darkness to produce the hormone melatonin, and melatonin protects our DNA, ultimately preventing cancer. If left to nature, our bodies would normally start producing melatonin after sunset. But we can’t all wake with the sunrise like Laura Ingalls Wilder, so we’re surrounded by bluish artificial light. Writes Boyle:

Shift workers, who rise with the night and work awash in blue light, experience not only disrupted circadian rhythms and sleep deprivation, but an increased risk of breast and prostate cancer.

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Thankfully, it’s not too hard to fix:

When we, in the industrialized world, do manage to turn off the lights, there are measurable, beneficial effects on our circadian rhythms.

Boyle offers several solutions: reddish rather than blueish light for bedtime reading, downward-facing streetlights to keep cities safe without lighting up the sky as much, and the free app f.lux, which makes your computer or phone’s screen subtly mimic natural light based on the time of day. You could also, I dunno, become a baker. I hear they wake up REALLY early.

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