Lack of sleep and lowering IQ. This article from Nymag.com makes interesting reading, especially if you are a parent....... 

"Despite how persuasive all this science is, somehow it still seems like a huge leap of faith to consider giving back an hour of our children's lives to slumber. Statistical correlations are fine evidence for scientists, but as parents, we want more—we want control. Dr. Judith Owens runs a sleep clinic in Providence, Rhode Island, affiliated with Brown. Recently, a father came in with his 15-year-old daughter, who was complaining of severe headaches. Interviewing the patient, Owens quickly learned that her daily routine was a brutal grind; after violin lessons, bassoon lessons, dance classes, and the homework from honors classes, she was able to get only five hours of sleep a night before waking every morning at 4:30 to hustle off to the gym. The father wanted to know if a lack of sleep could be causing her headaches. Owens told him that was probably the case. She recommended his daughter cut back on her schedule. The word probably made this father hesitant. He would let her cut back, but only if Owens could prove, in advance, that sacrificing an activity would stop the headaches. Sure, he knew that sleep was important, but was it more important than honors French? Was it more important than getting into a great college?  

Owens tried her standard argument. "Would you let your daughter ride in a car without a seat belt? You have to think of sleep the same way." But in the father's mind, he saw the transaction the other way around: Cutting back was putting his daughter at risk. What if the headaches didn't stop and she gave up one of her great passions, like dance, for no reason?........"