The study involved 15,659 adolescents in grades seven to 12. Data were collected from the teens and their parents.
Teens who reported that they usually sleep for five hours or less per night were 71 percent more likely to suffer from depression. They also were 48 percent more likely to think about committing suicide than teens who reported getting eight hours of nightly sleep. Both depression and suicidal thoughts were less likely in teens who reported that they “usually get enough sleep.”
Teens were more likely to have problems if their parents set a weeknight bedtime of midnight or later. They were 24 percent more likely to suffer from depression than teens who had to go to bed at 10 p.m. or earlier. They also were 20 percent more likely to think about committing suicide.
Teens with a bedtime of 10 p.m. or earlier got the most sleep. They reported sleeping for an average of eight hours and 10 minutes per night. This was 40 minutes more than teens with a bedtime of midnight or later.
“Our results are consistent with the theory that inadequate sleep is a risk factor for depression,” lead author James E. Gangwisch, PhD, told the AASM. “Adequate quality sleep could therefore be a preventative measure against depression and a treatment for depression.”
Seven percent of participants had symptoms of depression. Thirteen percent reported that they seriously thought about committing suicide during the past 12 months.
The NIMH notes that girls are twice as likely as boys to have had a major depressive episode by age 15. But males are much more likely than females to commit suicide. In 2006 suicide was the third-leading cause of death for young people between 15 and 24 years old.
Parents reported setting a wide range of bedtimes. Fifty-four percent of parents reported that their teen had to go to bed by 10 p.m. or earlier on weeknights. Twenty-one percent reported setting a bedtime of 11 p.m. Twenty-five percent reported setting a bedtime of midnight or later.
And most teens complied with the bedtime that their parents set. Seventy percent of teens reported going to bed on time. Overall, teens reported going to bed only about five minutes later on average than their bedtime.
The AASM reports that most teens need a little more than nine hours of sleep each night to feel alert and well rested during the day. But a shift in the timing of their body clock causes teens to feel sleepy later at night. This explains why it can be hard for them to fall asleep before 10 p.m.