Adolescents who don’t get enough sleep or who sleep poorly risk more than bad grades: Today’s poor sleep habits may be tomorrow’s hypertension, according to a National Institutes of Health–funded study of nearly 240 teens ages 13 to 16. Teens who had trouble falling asleep or who woke up too early were three-and-a-half times more likely to have elevated blood pressure. Sleeping fewer than six-and-a-half hours boosted risk 2.5 times. And 14 percent of study participants had prehypertension—meaning they don’t have high blood pressure now but are likely to develop it in the future—or hypertension with blood pressure levels in the 90th percentile for their height, age and gender. Study authors say adolescents need about nine hours’ sleep a night.