DENVER (CBS4) – U. S. teenagers are getting sleepier. According to a new study, up to a third of teens don’t get enough shuteye each night.

The study in the Journal Pediatrics found the  problem has gotten worse over the last 2 decades, and it’s affecting teenagers’ grades and their health.

Electronics and caffeine have been linked to sleep deprivation in teens, and there’s even a weighty issue. But getting enough sleep is essential.

“Adolescents need on average about 9 hours of sleep, and most teens in America are getting around 7,” said Dr. Lisa Meltzer, a pediatric sleep psychologist with National Jewish Health.

According to surveys taken of nearly 300,000 teenagers over 20 years, adolescents got less and less shuteye. The reasons for “the great sleep recession” are unknown.

“I think it’s a combination. I don’t think it’s one single factor,” Meltzer said.

Meltzer points to social media, smartphones and other electronics.

“The light that’s emitted from technology is enough to suppress melatonin, and you need melatonin to go to sleep,” she said. “Our brains have dimmer switches — it takes a while for them to slow down and go to sleep.”

The study suggests obesity is causing some sleep issues. Meltzer blames the stiff competition for college and early school start times. Lack of sleep can affect teens’ grades and their moods, and sleep deprivation is dangerous.

“Higher rates of depression, anxiety, higher risk for suicidal behaviors,” Meltzer said. “Make sleep a priority. We are a society that believes sleep is for slackers, and that’s the wrong message.”

LINK: Journal Pediatrics: “The Great Sleep Recession”