Pressures to be thin from girlfriends and the media significantly predict sleep duration, accounting for 4.5 percent of the variance in hours of sleep for adolescent girls, according to a new study. These pressures to be skinny were significantly predictive of sleep duration for white girls, but not for blacks or Hispanics. Together, the two predictors shared 6 percent of the variance in hours of sleep among white girls, with the strongest predictor being pressure to be skinny from girlfriends.