According to a recent study, obese teenagers who don’t get enough sleep may have problems with insulin secretion and blood sugar levels:
http://www.atlanticdrugs.com/news/sleep-reduces-diabetes-129.html
And teens who don’t sleep enough are more likely to be depressed, to drink sugared soda, to smoke cigarettes and so forth:
http://opinion.latimes.com/opinionla/2011/09/teenagers-and-sleep-another-thing-parents-do-wrong.html
http://www.frenchtribune.com/teneur/117430-8-hour-sleep-must-teenager
And other studies suggests lack of sleep may impact brain wiring:
While teenagers who go to bed early are much less likely to be obese and have a better chance of being physically fit:
http://www.medicalnewstoday.com/articles/235314.php
And further information on the importance of sleep for teens:
http://blogs.webmd.com/sleep-disorders/2011/10/sleep-deprived-teens-risky-business.html
http://www.huffingtonpost.com/jeff-deitz-md/children-sleep_b_1132517.html
http://buffalogrove.patch.com/articles/is-your-teen-sleep-deprived
A different study suggests teens may sleep TOO MUCH: