Up to 50% of women have some form of sleep apnea—a condition marked by pauses in breathing during sleep due to blocked airways—say researchers from Umeå University in Sweden. After studying a random sampling of 400 women ages 20 to 70, study authors were surprised to see that it wasn’t the usual sleep apnea symptom—daytime sleepiness—that gave women away; it was their high blood pressure.  MORE: 7 Signs You Aren’t Sleeping As Well As You Think You Are What’s a problem like sleep apnea got to do with hypertension? When you wake up in the middle of the night, your sympathetic nervous system pumps out adrenaline, causing blood pressure to rise, explains Steven Y. Park, MD, an otorhinolaryngologist and integrative sleep surgeon specializing in obstructive sleep apnea at Montefiore Medical Center in New York. “When sleep disruptions occur multiple times during the night, every night, blood pressure levels eventually come to stay elevated during the day,” he says. The adrenaline increase can also raise blood sugar and cholesterol levels, as well as up your chances of having a heart attack or stroke. And yet most docs miss high blood pressure as being a sign of sleep apnea. Why? Drowsiness during the day is still considered a hallmark sign of sleep apnea because it’s the telltale sign in men, says Dr. Park, and many experts still tend to consider men’s symptoms as standard indicators of a problem. But just like with heart attacks and strokes, “women’s bodies can respond to sleep apnea differently than men’s bodies,” he says. In fact, researchers of the new study say blood pressure screening should be used in diagnosing sleep apnea in women. For more info on sleep apnea—and whether that could be behind your high blood pressure—see How To Catch A Sleep Thief.