We all know getting too little sleep isn’t good for us, but did you know getting too much shuteye can make your memory worse, too?

A multi-year study of 15,000 women found that those who slept seven hours per night had the best memories, while those who slept five hours or less didn’t fare as well on memory tests.

But lolling in bed a lot longer than seven hours didn’t make the ladies’ brains any sharper — in fact, those who slept nine or more hours did just as poorly as the sleep-deprived participants.

“Women who got too little or too much sleep had the memories of women about two years [their senior],” said Elizabeth Devore, ScD, of Brigham and Women’s Hospital in Boston. And that was true for the test subjects in both mid-life and later on.

While Dean M. Hartley, PhD, director of science initiatives at the Alzheimer’s Association, pointed out the study doesn’t necessarily show cause and effect, he said, “Together with its other health benefits, including its role in protecting against heart disease and diabetes, this is yet another reason to get a good night’s sleep.”

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