If you have a lot of hourly employees, chances are they like overtime, or, more precisely, most of them like overtime pay. In 2016, the World Health Organization estimates that 488 million people worldwide worked at least 55 hours per week.

But evidence is emerging that excess overtime may be bad for workers’ health. A recent study from the World Health Organization found that people working more than 55 hours a week were 35 percent more likely than their peers working 35-40 hours a week to have a stroke and 17 percent more likely to die of heart disease. The study was methodologically sound; the authors published their protocol ahead of time, which is generally a sign of a robust analysis. But it was observational. Employees weren’t randomized to work longer or shorter hours.

So the somewhat histrionic headlines you may have seen about this study that scream, “Overwork Killed More Than 745,000 People In A Year,” should perhaps more accurately say, “working 55 hours or more per week was associated with 745,000 additional deaths out of a population of 488 million workers.” It is possible, after all, that other factors in these super-workers contributed to their bad outcomes. Salaried employees are more likely to have health insurance. Increasing workers’ wages tends to result in lower smoking rates. And we know that the routine stresses of life, like paying bills, paying for medications, finding childcare, and doing everyday routine self-care, are associated with worse health outcomes in people with less income. It’s possible to construct a mental model that, instead of blaming the excess vascular disease on the extra work hours, pins the blame on the workers’ lack of resources. In that model, the extra work hours are a symptom of the greater problem, not the cause of the health outcomes. In other words, are better outcomes in non-overtime workers due to working less overtime, or are they due to simply having more money?

Regardless, this study and others like it point to potentially beneficial strategies we could employ with our workforce. Some radical workplaces, arguing that the eight-hour workday is a relic of 19th-century socialism, have experimented with a six-hour workday, with special training for employees in increasing productivity. If the employees can accomplish in six hours what they used to achieve in eight, they get to keep the money they’d earn in eight hours, but they get two “free” hours a day. The company saves the overtime pay, saves the overhead of two more hours of office time per day, and if the study results at the top of this post are to be believed, saves the human and financial cost of additional disease burden.

Have you noticed any relationship between your overtime “super-users” and their health outcomes? Let us know what you’ve done about it, and we’ll share.

As the Medical Director of the Kansas Business Group on Health, I’m sometimes asked to weigh in on hot topics that might affect employers or employees. This is a reprint of a blog post from KBGH.