A few years ago, scientists conducted a real-world experiment at a ThyssenKrupp factory in Germany. They assigned the day shift to early risers and the late shift to night owls.

Soon the steel workers were getting an extra hour of sleep on work nights. By simply aligning work schedules with people’s internal clocks, the researchers had helped people get more and better rest.

“They got 16 percent more sleep, almost a full night’s length over the course of the week,” said Till Roenneberg, a chronobiologist at Ludwig-Maximilian University in Munich. “That is enormous.”

In recent years, U.S. educators have been paying increased attention to their students’ sleep needs and delaying school start times. Now a number of businesses are following suit, encouraging their employees to work when their bodies are most awake.

“It’s a huge financial burden not to sleep properly,” Roenneberg said. “The estimates go toward 1 percent of gross national product.”

Emerging science reveals that each of us has an optimal time to fall asleep and wake, a personalized rhythm known as a “chronotype.” When you don’t sleep at the time your body wants to sleep, you don’t sleep as well. That sets the stage not only for fatigue, poor work performance but also health problems ranging from heart disease and obesity to anxiety and depression.

A full 80 percent of people have work schedules that clash with their internal clocks, said Céline Vetter, an assistant professor at the University of Colorado at Boulder. “The problem is huge.”

Studies on workers in the call center of a mobile phone company, a packaging manufacturer and an oil transportation company show that these employees are more stressed and may experience more work-related discomfort and pain. It’s the mismatch — not the hours themselves — that matters. A 2015 Harvard Medical School study found that for night owls, working during the day increases diabetes risk.

Among the companies seeking to remedy the problem is Southwest Airlines, which allows pilots to choose between morning and evening schedules. The U.S. Navy traded an 18-hour submarine shift schedule for a 24-hour one that more closely matches sailors’ biological rhythms.

“I think circadian rhythms will be a huge issue for human resources in the future,” said Camilla Kring, a Danish consultant who has helped employees at AbbVie, Roche, Medtronic and other companies learn to respect their natural sleep cycles. “It really makes sense to think about when people have the most energy and when they’re peaking mentally.”

Worker fatigue has played a role in many workplace accidents, most famously the Challenger space shuttle explosion and the Exxon Valdez oil spill.

Chronotypes shift in a predictable way. Between ages 12 and 21, everyone’s natural sleep schedule gets about 2½ hours later. After that, chronotype creeps in the other direction, which is why older people typically find wake earlier than they used to.

But chronotype also orchestrates peaks and troughs of energy over the course of the day. The “window of circadian low,” the hours when the body is least adapted for wakefulness, typically occurs between 2 and 6 a.m. There a smaller dip 12 hours later.

There are also two high points, when thinking is sharp and reaction times quick. One occurs within an hour or two after waking, and the other after the daytime dip. This cycle is shifted earlier in a morning person and later in a night person.

At pharmaceutical company AbbVie, employees design schedules that take advantage of their biological strengths. A nine-hour training program helps them identify when they are ripe for creative or challenging projects. Lower-energy periods are meant for more mundane tasks. Employee satisfaction with work-life balance has risen to nearly 100 percent, from 39 percent 10 years ago.