(Reuters Health) - Teens who get too little sleep may be more likely to engage in risky behaviors like drinking, smoking, and unprotected sex than their peers who get enough rest at night, a study of U.S. high school students suggests.

Roughly seven in 10 American high school students average less than eight hours of sleep a night, falling short of the recommended eight to 10 hours adolescents need for optimal physical and mental health, the study found.

Compared with teens who got at least eight hours of sleep, high school students who got less than six hours were twice as likely to drink alcohol, almost twice as likely to use tobacco, and more than twice as likely to use other drugs or engage in risky sexual activity.

High school students who got less than six hours of sleep a night were also more than three times more likely to engage in self-harm activities or to contemplate or attempt suicide, compared to teens who got eight hours or more of sleep on a typical night.

While the study wasn’t a controlled experiment designed to prove whether or how sleep might directly impact teen behavior, it’s possible that insufficient sleep leads to changes in the brain that make risky behavior more likely, said lead study author Matthew Weaver of Brigham and Women’s Hospital and Harvard Medical School in Boston.

“One possible physiologic mechanism is that insufficient and poor quality sleep is associated with reduced activation of the prefrontal cortex, an area that is critical for executive function and logical reasoning,” Weaver said by email.

“Regions of the brain that are related to reward processing are also affected, potentially leading to more impulsive and emotionally-driven decisions,” Weaver added.

His team examined nearly 68,000 surveys completed by high school students between 2007 and 2015.

During the study period, the proportion of students reporting less than eight hours of sleep on an average school night rose from 68.9 percent to 71.9 percent, researchers report in JAMA Pediatrics.

Youth with the lowest average amounts of sleep - less than six hours - had the highest rates of unsafe behaviors. But researchers also found risks associated with six or seven hours a night.

For example, teens who got seven hours of sleep a night were 28 percent more likely to drink, 13 percent more likely to smoke, and 17 percent more likely to try drugs other than marijuana, compared to adolescents who got at least eight hours of shut-eye.

One limitation of the study is that it relied on teenagers to accurately report their sleeping habits and risky behaviors, the authors note. It’s also possible that factors not measured in the study might impact both sleep times and risky behaviors.

Parents may have a hard time getting teens to bed early, but they can still take steps to ensure adolescents get enough rest, said Dr. Sujay Kansagra, director of the Pediatric Neurology Sleep Medicine Program at Duke University Medical Center in Durham, North Carolina.

“Families should work together to set guidelines for sleep and achieve common goals, such as improved grades, better mood, and more energy, and parents should advocate against caffeine and late night electronic use as both can disrupt sleep,” Kansagra, who wasn’t involved in the study, said by email.

And it’s important that parents lead by example.

“It’s hard to ban your adolescent from consuming caffeine while you have a cup of coffee in your hand,” Kansagra said.

SOURCE: bit.ly/2RgqFIL JAMA Pediatrics, online October 1, 2018.