Could City Lights Put You at Risk for Breast Cancer?

Photo: Stocksy/Jovo Jovanovic
Living in an urban or suburban area means that, inevitably, you're going to be around light at night. And in some places, it stays really bright 24-7 (hey there, Times Square, Tokyo, and the Vegas Strip).

So what's wrong with that? (Besides the obvious challenges in getting sufficient rest in places like the City That Never Sleeps.) According to a new study from Harvard Medical School, women who are exposed to outdoor light at night could be at a higher risk of breast cancer than women who live in places where there's less artificial light.

In a paper published online in Environmental Health Perspectives, researchers examined data, collected between 1989 and 2013, on nearly 110,000 female nurses (most of whom were white and premenopausal). The study found that the top fifth of women who were most exposed to outdoor light at night had a 14 percent greater risk of breast cancer than those women in the bottom fifth of exposure.

Women who were exposed to the most outdoor light at night had a 14 percent greater risk of breast cancer.

So, for everyone who doesn't want to go to bed with the sun, can I just say: Yikes. And this isn't the first time researchers have looked into the possible link between light and cancer—previous studies have shown that being around artificial light at night can lead to a disruption of circadian patterns (one of the big reasons you feel jet-lagged when you jump across time zones) and a decreased secretion of melatonin, a sleep-regulating hormone. All that can mess with the body's ability to regulate estrogen, which could be a potential factor in an increased risk of breast cancer.

In this latest study, the link between exposure to light at night and breast cancer was only present for women who were premenopausal (typically, that's women younger than 50). It was also there among women who currently or had previously smoked, according to the study's lead author, Peter James, ScD. The link was also stronger among the women who worked night shifts.

Before you go quitting your night shift or throwing out all your cigarettes (actually, that might not be such a bad idea), know that more work needs to be done before scientists can definitively say that being around light at night leads to a greater risk of breast cancer. Still, being proactive about self-exams and screenings (and giving your girls some TLC once in a while) never hurts.

There are other ways to make your evening routine more healthy without moving to the country: Skip the binge-watching (sorry, Netflix) and practice "digital minimalism."

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