The 4-day workweek: Science explains why it could improve our minds, bodies, and companies' bottom lines

• A four-day workweek UK trial had promising results: less stress, better sleep, and no revenue loss.
• Science explains why the four-day workweek could be good for employees and employers alike.
• The UK trial is limited, but a shorter workweek could improve employee wellbeing and productivity.

The four-day workweek is more enticing than ever after a 61-company trial in the UK found almost no downsides and a heap of benefits.

The nonprofit 4 Day Week Global organized the pilot program and published promising results on Tuesday: The 2,900 workers in the trial reported lower levels of stress, anxiety, burnout, fatigue, and sleep issues, alongside better work-life balance. For the 47 companies that reported financial data, revenue largely stayed the same.

That all makes sense to Philip Gehrman, a psychologist at the University of Pennsylvania.

"As much as work can be rewarding and fulfilling, it's also stressful and takes time that we'd like to spend doing other things. So it just seems logical to me that working fewer hours would be associated with a range of improvements," Gehrman told Insider.

The UK trial was limited, so take the results with a few grains of salt. There's no control group — a company or companies that maintained a five-day workweek, to compare against the four-day workweek companies.

There's also a risk of "selection bias" — a particular type of company may be far more likely to volunteer for a four-day workweek trial. Maybe they're especially receptive to their employees' wellbeing, for example, or they like to experiment and take risks. That could skew the results, meaning they don't represent most employers or workplaces.

The participating companies also weren't required to use the same schedule. Employers could nix Fridays, allow staff to work shorter hours over a five-day workweek, implement an average 32-hour week over the course of a year, or make the four-day week contingent on meeting performance targets.

All in all, the trial lasted six months. Gehrman said he would like to see a longer study to know whether the positive effects last.

Still, other research on human brains and behavior supports the idea that less time on the job could be better for workers and their employers. Here's what science has to say about the UK four-day workweek trial results.

Our brains like deadlines

Having a shorter workweek could add a little extra pressure to work efficiently. That's because human brains sometimes work best on deadlines, according to Alex Korb, a neuroscientist at the University of California, Los Angeles.

"It helps us focus our energy and our efforts," he told Insider. "If I said you had some big project that was really difficult to do, and I didn't give you a deadline, well then it would probably take a really long time, and you might not make much progress at all."

Research has shown that people tend to increase their effort as a deadline approaches.

"People are not robots. Most of the time, we're not working at our peak," Korb said. "It's probably not even possible for people to work at their peak for eight hours a day, five days a week."

So shortening the workweek would cut some of that non-peak time, he said.

Fewer workdays can reduce (or compress) stress and improve focus

To state the obvious: Work can be stressful. Just waking up in the morning knowing you're about to work can cause your body to release higher levels of the stress hormone, cortisol, than it would on the weekend, two studies have found.

That's not necessarily bad. But prolonged stress, and too much cortisol over time, can contribute to a range of physical and mental health issues.

"If suddenly you had an extra weekday — well, instead of five days of elevated cortisol, you only have four days of elevated cortisol," Korb said. "That could certainly explain why people experience reduced burnout and improved mood."

Stress can also activate the body's fight-or-flight response and disrupt focus, leading to poorer job performance. Fewer stressful days could lead to more focused, effective workers.

Indeed, the UK trial reported small decreases in stress: on a scale of one to five, participating workers reported average stress levels of 3.07 before the trial, and 2.74 after the trial.

The four-day workweek could backfire in some cases, though: People who are expected to complete the same workload in less time could end up more stressed. That's what happened to 13% of workers in the UK trial, while 39% reported feeling less stress.

Sleeping well makes everything better

Americans have a sleeping problem. Over a third of US adults don't get the recommended seven hours or more each night, according to a 2016 report from the Centers for Disease Control and Prevention.

With fewer hours of work, though, people would have more time to sleep. Cortisol, too, can affect sleep quality, so having fewer high-cortisol days (ahem, work days) may mean fewer days of meager sleep.

"One of the first things that goes out the window when people are stressed is their sleep," said Gehrman, who directs U Penn's sleep neurobiology and psychopathology lab.

"When people don't get enough sleep during the week, and they sleep in on the weekends, that two days of sleeping in is not enough to eliminate the effects of five days of inadequate sleep," he added. "But three nights of recovery for four nights of sleep loss is definitely better."

In the 4-day work week pilot, 46% of employees reported less fatigue than usual. In turn, that could allow them to focus better on the job.

A shorter workweek probably wouldn't completely resolve America's sleeping woes, though.

"I think it could be a piece of the puzzle," Gehrman said. "It may not change the overall cultural attitudes towards the importance of sleep."

More time for chores, hobbies, family, and friends can benefit everyone

Workers in the UK trial reported having more time for housework, cooking, caring for others, social obligations, and hobbies. An abundance of research shows all of that is good for both mental and physical health.

A shorter workweek might mean fewer sick days

The UK report observed a decrease in absenteeism — the number of sick days or personal days employees took — but concluded that the drop was not statistically significant.

It is possible, however, that a shorter workweek could result in fewer sick days in the long run. That's partially because of basic statistics: There's a lower probability of illness falling on a workday when fewer of your days are workdays.

But there is also a strong link between cortisol, sleep, and the immune system. Over time, too much cortisol can impair the immune system, while sleep can restore it.

It could also help retain employees

The UK companies also reported fewer employees quitting their jobs during the trial period. Korb said there could be a simple reason for that.

"Employees see the inherent value in having a four-day workweek, and if suddenly it feels like the company is actually interested in my wellbeing ... well, then it makes me more motivated to want to work for the company," he said.

"I want to care about the company, because I feel like the company cares about me."