Sleeping with a television on is associated with weight gain among women. New research shows that women who slept with a light or a television on were 17-percent more likely to have gained at least eleven pounds over the course of five years. Those who slept with just a small nightlight or no light showed no significant weight gain. Several light sources impair the body’s ability to create the sleep hormone melatonin. The research is published in JAMA Internal Medicine.