Later School Times Suggested by American Academy of Pediatrics

Dr. Judith Owens, director of sleep medicine at Children's National Medical Center in Washington has recently submitted a policy statement requesting that school districts delay starting times for morning classes.
Recent research has shown that adolescents who get enough sleep have a reduced risk of being overweight or suffering depression, are less likely to be involved in automobile accidents, and have better grades, higher standardized test scores and an overall better quality of life. Studies have shown that delaying early school start times is one key factor that can help adolescents get the sleep they need.

Many school districts are debating the change; the Long Beach, California, school board voted last year to delay the start of middle school until 9 a.m. But it’s a complex issue with school boards, educators and parents struggling to balance bus schedules, after-school activities and work schedules for older students. 

Nonetheless, Owens says biology should trump convenience. She notes that when teenagers go into puberty, there are changes in their circadian rhythm, the body's natural clock that regulates sleep and wake patterns. At the beginning of adolescence there is a natural delay in sleep and wake times, so that the average teenager doesn't fall asleep until around 11 pm.
 However, they also need between eight and nine hours of sleep per night so they are biologically programmed to wake at around 8am, when they're already in first period class. Teens often sleep in over the weekend, and many teen habits make it even harder to fall asleep which makes matters worse. But parents can help: it's especially important to set limits on the nighttime use of electronics. Studies have shown that the light from an tablet or cell phone can keep the brain in a waking, excited state. Quick naps late in the afternoon for 20 minutes or so can take the edge off and temporarily restore alertness.

A separate study published this month in the Journal of Pediatrics found that teenagers who don’t get enough sleep are more likely to become obese. Shakira Suglia of the Mailman School of Public Health at Columbia University and colleagues found that about a fifth of the 16-year-olds reported getting less than six hours of sleep a night, in a survey of 10,000 teens and young adults. Those with less sleep were 20 percent more likely to be obese by age 21, compared to their peers who got more than eight hours of sleep

 “Lack of sleep in your teenage years can stack the deck against you for obesity later in life,” Suglia said in a statement. “Once you’re an obese adult, it is much harder to lose weight and keep it off. And the longer you are obese, the greater your risk for health problems like heart disease, diabetes, and cancer.”

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Read more:
Houston Sleep.net
Teen Sleeplessness Piles on Risk for Obesity

Sleep deprivation isn't always obvious.

"Sleep debt" (or sleep deficit) is the difference between the amount of sleep you should be getting and the amount you actually get. This difference represents a deficit which increases every time we skim some extra minutes off our nightly sleep.
"People accumulate sleep debt surreptitiously," says psychiatrist William C. Dement, founder of the Stanford University Sleep Clinic. In fact, studies have shown that such short-term sleep deprivation leads to a "foggy brain", worsened vision, impaired driving and problems in short-term memory. Long-term effects include obesity, insulin resistance, and heart disease.
And most Americans suffer from chronic deprivation. A 2005 survey by the National Sleep Foundation reports that, on average, Americans sleep 6.9 hours per night -6.8 hours during the week and 7.4 hours on the weekends: experts recommend eight hours of sleep per night.
The problem is that after a long period of sleep deprivation, you stop realizing how tired you actually are.

In a study by the University of Pennsylvania School of Medicine, researchers followed three groups of subjects for 14 days; one group slept for eight hours a night, the second group slept for six hours a night, and the third group slept just four hours a night. Cognitive tests after the two-week period showed that the people with only six hours of sleep a night showed similar reaction times as people with a blood alcohol content of 0.1 percent; a level which is considered legally impaired.

Other studies have indicated that a consistent lack of sleep may cause permanent damage to your brain. 
One in particular, also conducted by the University of Pennsylvania School of Medicine and published in The Journal of Neuroscience looked at lab mice that were kept awake to replicate the kind of sleep loss common in modern life, through night shifts or long hours in the office.
The team studied certain brain cells which are involved in keeping the brain alert. After several days of sleep patterns similar to those followed by night workers - three days of night shifts with only four to five hours sleep in 24 hours - the mice lost 25% of the brain cells in vital parts of the brain stem.

After only a night or two of sleep deficit, a few nights of adequate sleep are usually enough to reverse the effects and "recharge" your system. But chronic sleep deprivation may be harder to recover from.
For information on how to increase your sleep drive and improve your waking hours, take a look at our  sleep hygiene recommendations. If you have a problem with daytime sleepiness and you have increased your sleep length without improving your daytime sleepiness, then you should be evaluated by a Sleep Disorders Specialist. With proper care most people can obtain the treatment they need to improve this problem.

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References:
Sleep-Deprived People Can’t Tell They’re Sleep-Deprived; Melissa Dahl, NYMag.com
Lost sleep leads to loss of brain cells, study suggests; Helen Briggs, BBC News