The light emitted from using devices at night can increase a woman’s risk of infertility, as reported by Shape.

Researchers from UCLA, Osaka University, and the Japan Science and Technology Agency looked at how exposure to artificial light at night affects the fertility of female mice and found that not only did darkness matter, but so did the age of the mice. When exposed to traditional day-night light patterns, older mice approaching rodent menopause (yes, that’s a thing) were able to get pregnant 71 percent of the time. But when they were exposed to artificial light at night, that number dropped to 10 percent. The light variation disrupted the fertility of younger mice as well, but not nearly as drastically. (These Affordable Products Can Help You Have a Better Night’s Sleep.)

So what do light at night and fertility have to do with each other? The connection has to do with your body’s circadian rhythm, that “internal clock” which controls a variety of biological functions including your menstrual cycle. Sleep in general has been shown to improve fertility in both women and men, but this study shows that melatonin—the hormone that helps regulates your sleep cycle—is a crucial factor to that improvement.

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