PeopleImages via Getty Images An estimated 90 percent of American high school students are chronically sleep-deprived, according to a 2014 survey.

Delaying school start times has been universally touted as the answer to the growing epidemic of teenage sleep deprivation, but this common orthodoxy may be based in false ideas about how teen biological clocks really work.

The argument for later start times hinges on the fact that teenagers prefer to go to bed and sleep in later because of a delay in their circadian clocks that govern the body’s rhythms of sleep and waking. To be more in line with teens’ “natural” sleep patterns, thousands of U.S. high schools have pushed back their morning schedules in recent years.

But the solution may not be so simple, according to new research from Harvard Medical School and the University of Surrey in the U.K.

The research collaboration between mathematicians and sleep scientists used a complex mathematical model to show that delaying school start times is unlikely to do much to ease high school students’ sleep deprivation.

Why? Because teenagers with later school start times stay up even later in the evenings, thereby increasing their exposure to artificial light, which can further mess with their circadian rhythms. A far more effective solution to teenage sleep deprivation, the study’s authors suggest, would be to turn down the lights and limit screen time in the evenings. (Or better yet, keep devices out of the bedroom altogether.)

“"The use of artificial light in the evening is in large part responsible for adolescents sleeping later."” - - Dr. Andrew Philips, Harvard sleep scientist

“The potential benefits of shifting school start times later can unfortunately be undermined if individuals do not also carefully manage their use of artificial light,” Dr. Andrew Philips, a sleep scientist at Harvard and one of the study’s lead authors, told The Huffington Post. “This is especially true for individuals with a tendency to be later sleepers.”

For the study, published Monday in the journal Scientific Reports, the research team created a mathematical model to show how British teenagers’ circadian clocks respond to light and how this determines the time at which they fall asleep. The model accounts for whether an individual is a morning or an evening person; the impact of natural and artificial light on the body’s clock; and the time that their alarm clock usually goes off.

In developing their model, the researchers took inspiration from Huygens, a 17th century Dutch mathematician, who studied how a person’s body clock could synchronize with the environmental clock.

The analysis showed that later start times didn’t mediate sleep loss. It did show, however, that young peoples’ light consumption interfered with their natural clock. The researchers found that getting up later in the morning resulted in teens staying up later at night, increasing their exposure to artificial light. They ended up going to bed even later and sleeping in later as a result, while suffering from worse sleep quality.

Poor sleep among young people is a growing issue with wide-ranging implications. Teenagers need roughly nine hours of sleep, according to the National Institutes of Health, but less than 10 percent are actually getting it. This chronic sleep deprivation comes at an enormous cost, including poor academic performance, issues with learning and memory, mental health conditions, and physical health complications including diabetes and obesity.

Resetting the Biological Clock

Without artificial light, people would wake up with the sunrise. Teenagers, whose body clocks “run slow,” are particularly vulnerable to the effects of artificial lighting.

“From research over the last few decades we know that body clocks typically run a little slow, so they need to be regularly ‘corrected’ if they are to remain in sync with the 24-hour day,” Philips said. “Historically, this correcting signal came from our interaction with the environmental light/dark ‘clock’.”

We know from a large body of science that the circadian rhythms of people of all ages are extremely sensitive to artificial light exposure, and using light-emitting devices after dark delays the timing of the circadian clock.

Indeed, increased exposure to artificial lighting seemed to only enhance the delay in the students’ biological clocks. In a new paper slated for publication in the Journal of Biological Rhythms, the same research team showed that modern use of artificial light has allowed people who have a tendency towards being late sleepers to become extremely late sleepers, sometimes to their own detriment.

“[It’s] been suspected that our modern usage of artificial light is responsible for our much later sleep times compared to our pre-industrial ancestors,” Philips said, “as well as our tendency to have differently timed sleep on weekends compared to weekdays.”

But the researchers noted that start times in the U.K. are generally later than in the U.S., where many schools begin as early as 7 a.m. In American high schools, the study’s authors concluded, there may be some benefit to modestly delaying school start times in addition to educating teens about the effects of artificial light and excessive evening screen time.