"Too Much Work" by Jason Wheeler, Flickr Creative Commons

Last week, a study published in the British medical journal the Lancet had an alarming warning for people who work more than 55 hours a week: They appear to have a 33 percent higher risk of stroke than those toiling a more sane 35 to 40 hours each week, and a 13 percent increased risk of coronary heart disease, too.

If that sounded familiar, there's a reason. A growing number of studies are examining the link between long hours, health problems and productivity. And what they're finding isn't pretty.

A study last year found that that working more than 55 hours a week at low-income jobs is associated with a higher risk of developing Type 2 diabetes. Another study tied prolonged sitting with early death, and reported the worst results for older women who were inactive for 11 or more hours a day; another found the odds for developing depression were more than double for those who work very long hours.

These are just a few examples. Prior studies have associated working more than 11 hours a day with higher risks of heart attack. Researchers have found a link between working more than 55 hours a week and greater issues with sleep disturbances. Others have recently done a "meta-analysis" of other published research and found that workaholics are more likely to drink "risky" levels of alcohol, too.

Meanwhile, it's not just problems with workers' health that are linked with overwork--productivity and cognitive function appears to suffer, too. For instance, last year, a Stanford researcher published a study showing that productivity begins to fall off at about 50 hours per week. After 55 hours, it plummeted, with no discernible difference in output for those who worked 70 versus 56 hours a week.

As the Economist put it: "That extra 14 hours was a waste of time."

Those reading closely might be wondering: What is it about 55 hours a week, or 11 hours a day over a five-day work week? Is it some kind of magic overtime threshold that's the equivalent of falling off a health or productivity cliff?

We reached out to a couple of researchers who worked on a few of these studies with that question. One, Marianna Virtanen, of the Finnish Institute of Occupational Health, said 55 hours is a common cut-off used in earlier research, but that there's no particular reason for it, noting she uses other categories of hours, and that another common one is 48 hours. That's derived from the EU's Working Time Directive, she said, which is meant to limit the work week to 48 hours on average.

Indeed, the stroke study found that those who work 49 to 54 hours a week see a 27 percent higher risk; the one that looked at alcohol indulgence found the most "risky" use in that same range of hours. Mika Kivimaki, one of the co-authors on the stroke study, called 55 hours a "convention," noting that he first saw the 55 hour a week threshold used back in 1998. After that, he said in an e-mail, "most studies have used the same cut off probably to make comparisons between studies easier."

Whatever the reason, toiling 55 or even 49 hours a week looks pretty bad for workers' health and how effective they are at getting things done. And while that may be dispiriting news for any workaholics, the average employee is still under that threshold--at least for now. According to Gallup, the number of hours put in by the average U.S. worker is on the rise, but it's still at just under 47 hours a week.

Read also:

Working lots of overtime? Your risk of stroke may increase, study finds.

A business upside to Obama's overtime move

Americans are trading sleep for work, and it’s literally killing us

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