Studies show that, over time, working long hours can increase your risk of depression, heart attack, and heart disease.

It seems that working long hours has many insidious effects on health and wellbeing. Low on free time, workers may abandon good habits that counteract the negative effects of a high-stress lifestyle, choosing to skip the workout, opt for takeout vs. a home-cooked meal, or skimp on sleep. And overworking certainly cuts into focused time with family and friends.

But beyond the obvious effects on health, working too much can actually impair cognitive function. In one five-year study published in the American Journal of Epidemiology, participants completed a variety of tests to evaluate intelligence, verbal recall, and vocabulary. Compared to those who worked 40 hours per week, those who worked 55 hours per week showed poorer vocabulary and reasoning.

“We actually get stupider when we work too much,” says executive coach Tasha Eurich, Ph.D., author of the new book “Bankable Leadership.” Eurich says working fewer hours and taking more breaks and occasional vacations can help us become much more productive.

In fact, working more doesn’t have the positive effect on productivity you might expect. Overtime only works in short bursts, and when sustained, does not increase productivity and may actually hamper it.

According to one study, outlined by social futurist Sara Robinson on AlterNet, after working 60 hours per week for eight weeks, “the fall-off in productivity is so marked that the average team would have gotten just as much done and been better off if they’d just stuck to a 40-hour week all along. And at 70- or 80-hour weeks, the fall-off happens even faster: At 80 hours, the break-even point is reached in just three weeks.” What’s more, when teams who have worked overtime for a sustained period resume a 40-hour workweek, it takes time to recover from the burnout and reach the same productivity level that they started at.

Indeed, many Americans worked six days a week before the five-day, 40-hour workweek was popularized by Henry Ford in the 1920s. He instituted the new working hours for his employees at Ford Motor Company, in part, to give them more time with family, but also to increase their productivity.

Of course, Weisenthal argues that some people are so passionate about their jobs that they’d do the work in their free time anyway. I’ve certainly spoken to several startup CEOs in the tech sector who say disconnecting can actually make them more anxious, since they want to know what’s happening.

But even the lucky ones who love their jobs should consider stepping back. In a study that was conducted even before the economy supercharged work, economist Sylvia Ann Hewlett found that 45% of managers in large companies worked “extreme jobs,” marked by 70-plus-hour weeks, grueling travel schedules, and limited vacation time (nearly 60% didn’t take the time allotted them).

Many of these workers loved their jobs, and called them “exciting,” “an adrenaline rush,” and “addictive.” However, they took a serious toll on their intimate relationships and their health. “Close to 50% of extreme workers are so depleted and drained when they get home at night that they’re speechless — incapable of conversation,” writes Hewlett in an article for the Harvard Business Review. “This can be rough on partners and spouses.” Her research also found links between long hours and chronic insomnia, weight gain, infertility, and heart problems.

So no matter how much you love what you do, occasionally walking away may be the best thing for you and your long-term success.