"Women are constantly being told that they need a lot of sex—they feel like they should be walking around feeling desirous all the time," says Hilda Hutcherson, MD, clinical professor of obstetrics and gynecology at Columbia University Medical Center. "But it's more common to have ebbs and flows." The average couple has sex about six times a month, which, as Hutcherson points out, means that many women are having much less than that. Even occasional sex gives your heart rate a healthy boost and delivers a rush of endorphins (which enhance mood) and prolactin (which improves sleep).

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