*The following is excerpted from an online article from the HealthDay.
American teens don't get enough sleep, and the problem has only gotten worse since the 1990s, new research shows.
Just 63 percent of 15-year-olds reported getting seven or more hours of sleep a night in 2012. That number is down from 72 percent in 1991, according to the study.
Regardless of the time period studied, the number of teens reporting seven or more hours of sleep nosedives between the ages of 13 and 18, the study showed. At 13, roughly two-thirds of teens get at least seven hours of sleep a night; by 18 that percentage drops to about one-third.
"After age 16, the majority are not meeting the recommended guidelines," said study author Katherine Keyes, an assistant professor of epidemiology at Columbia University's Mailman School of Public Health in New York City.
Sleep experts have noted that too little sleep boosts the risk of weight gain, poor school performance, depression and other problems.
The study is published online Feb. 16 in Pediatrics.
For the study, researchers from Columbia University looked at sleep data from a national survey of more than 270,000 teens from 1991 to 2012. Each year, teens reported how often they got seven or more hours of sleep, as well as how often they got less sleep than they need.
The most recent recommendation from the National Sleep Foundation says teens aged 14 to 17 need eight to 10 hours a night and people aged 18 to 25 need seven to nine hours.
The largest declines in those getting enough sleep occurred between 1991 through 2000; then the problem plateaued, Keyes said.
The researchers also found gender differences in sleep. "Girls are less likely to get an adequate amount of sleep compared to boys," she said.
One worrisome finding, she said, was that some teens who weren't getting enough sleep often thought their sleep duration was fine.