When it comes to working consistent long hours without taking proper time off, like so many of us have accepted as the new normal these days, the research is clear - it's not only a terrible idea for employees, but it also doesn't provide any benefit to your boss or your company.

In fact, in a cruel twist of fate, people who regularly put in 80-hour work weeks can often end up less productive than staff members who head home at 5pm every day, the studies suggest.

Over at the Harvard Business Review, journalist Sarah Green Carmichael analysed the published research in an attempt to try to understand why people in many developed countries are now working longer hours than ever before. 

She found that not only is there no evidence to suggest that working for longer increases productivity, there's also a whole slew of research out there that demonstrates the opposite.

Back in April, a study led by Erin Reid from Boston University found that mangers couldn't tell the difference between consultants who worked 80 hours, and those who just pretended to. "While managers did penalise employees who were transparent about working less, Reid was not able to find any evidence that those employees actually accomplished less, or any sign that the overworking employees accomplished more," writes Green Carmichael.

Not only that, but studies have also found that pulling those kinds of hours regularly increases employee stress and burnout, and contributes to a range of health problem, from impaired sleep, depression, diabetes, heavy drinking and heart disease. A couple of weeks ago we reported on research that linked longer working hours to a significantly higher risk of stroke. 

All that stress and illness takes a financial toll on companies, increasing absenteeism, staff turnover, and rising health insurance costs

And then there are all the mistakes we make. A 2010 study published in Sleep found that sleep deprived participants were worse at recognising other people's emotions and social cues. Tired people also struggle to make good decisions, which is a pretty crucial part of almost every job.

The real twist of the knife is the fact that scientists have actually known for more than a century that overwork doesn't equal productivity. 

"In the 1890s employers experimented widely with the 8-hour day and repeatedly found that total output per-worker increased," workplace researcher Tom Walker wrote in 2004. "In the first decades of the 20th century, Frederick W. Taylor, the originator of 'scientific management' prescribed reduced work times and attained remarkable increases in per-worker output."

As Green Carmichael reports, over a century later, the Harvard Business School repeated this experiment with knowledge workers rather than labour workers, and it still held true. 

"Predictable, required time off (like nights and weekends) actually made teams of consultants more productive," explains Green Carmichael. "In sum, the story of overwork is literally a story of diminishing returns: keep overworking, and you'll progressively work more stupidly on tasks that are increasingly meaningless."

It's probably unsurprising at this point to mention that researchers in the US showed earlier this week that cutting school down to just four days a week can actually improve some areas of academic performance. Early research has suggested the same might be true for the working week.

So with all the research out there pointing in one clear direction, the real question is, why are we still killing ourselves with 14-hour days if there's never been any evidence to suggest that it makes us better employees? And that answer is, unfortunately, not so clear, Green Carmichael admits:

"It could be ignorance. Maybe most people just don't know how bad overwork is, objectively speaking … Maybe they've seen the research, but just don't buy it (or choose to act on it). Or it could be something stronger. Maybe when you combine economic incentives, authority figures, and deep-seated psychological needs, you produce a cocktail that is simply too intoxicating to overcome."

Maybe it's time we all stopped linking our existence so closely to our jobs and started to plan our work routines around science-backed evidence, rather than letting ourselves be guilted into spending the best years of our lives trapped inside an office.