About 70 percent of U.S. high school students don\'t get enough sleep on school nights and this is linked to health-risk behaviors, researchers say. Scientists at the Centers for Disease Control and Prevention, who conducted the study, said insufficient sleep is associated with a variety of health-risk behaviors, including: physical inactivity, drinking alcohol, smoking cigarettes, drinking soda, fighting, being sexually active, marijuana use and seriously considering attempting suicide. High school students participating in the 2007 national Youth Risk Behavior Survey were asked, \"On an average school night, how many hours of sleep do you get?\" The study, published online by Preventive Medicine, said 68.9 percent of adolescent responders reported insufficient sleep on an average school night. Insufficient sleep was considered less than 8 hours and sufficient sleep 8 or more hours of sleep. Students who reported insufficient sleep were more likely to engage in the health-risk behavior than students who reported sufficient sleep, researchers said. \"Many adolescents are not getting the recommended hours of sleep they need on school nights. Insufficient sleep is associated with participation in a number of health-risk behaviors including substance use, physical fighting, and serious consideration of suicide attempt,\" Lela McKnight-Eily of the CDC said in a statement. \"Public health intervention is greatly needed, and the consideration of delayed school start times may hold promise as one effective step in a comprehensive approach to address this problem.\"