Are you a victim of vacation deprivation? Odds are, you are. And that has enormous possible consequences for your health and happiness as well as the economy.

Would you let your boss withhold a paycheck or two from you, just because? You would not. Except maybe you are doing exactly this to yourself by not taking the vacation days you are owed. And if you don’t take those days by year-end you just may have lost them forever. Said travel consultant Kim Zielinski: “If one forfeits earned vacation, that means you essentially end up working those days for free.”

The numbers - from multiple sources - underline that we just don’t take the vacation days we are owed. A recent Expedia study said that the average American worker gets 15 vacation days but takes only 11.

We are not the world’s worst. That dubious honor goes to South Korea. “South Koreans are the world’s most vacation deprived workers – while they’re offered 15, they take only 6 days off within a given year,” said Expedia.

But we are near the bottom. Per Expedia, “Mexican workers give back three of 15 available days, while Canadians take the full 15 available to them.”

Expedia added: “Europeans are the world’s least-deprived vacationers: workers in Germany, France, Italy, Spain, Sweden, Denmark and Finland are all offered 30 days off. The Germans, French, Spanish and Finnish use nearly all of those days, while the Danish take 28, Italians take 25 and Swedes take 25.”

That means we take less than half the vacation days European workers take.

There's still more troubling news.

“Over the past 15 years we have gotten worse about using available vacation days,” said Cait DeBaun, an executive with Project: Time Off in Washington, DC.

The math gets complicated as more companies switch to a single bucket, Paid Time Off program (where vacation days, sick leave, personal days off are all thrown in the same pot). But we are still leaving days unused. Lots of them. Another study sponsored by Project: Time Off found that the average American worker has 21 days in a PTO bucket but uses only 77%, which means 4.9 days go unused.

Is that time necessarily lost? Not always. Some companies allow unused vacation days to be banked; some states have in fact made “use it or lose it” policies regarding vacation illegal. But that Project: Time Off study nonetheless found that maybe 23% of the unused PTO time simply vanished.

The irony: workers who take their vacations may be happier, more productive employees, said Charles McCool, who teaches travel skills workshops to employee groups.

“Time off is essential to our personal health," said DeBaun. "Employees are more productive.” 

The landmark Framingham Heart Study, for instance, showed that men who did not take a vacation for several years were 30% more likely to have a heart attack than men who take vacations. Women fared as badly. Ones who did not take a vacation once in every six years were eight times more likely to have a heart attack or develop coronary disease, compared to women who vacationed at least twice a year. Not taking time off also may be bad for the economy.

In analysis for Project: Time Off, Oxford Economics found that unused vacation days are a huge liability on the books of American companies. Said Oxford Economics, $224 billion is the total liability. Project: Time Off added: “According to Oxford’s analysis, the average vacation liability per employee is $1,898 and in some companies studied is more than $12,000 per employee.”

So, why don’t we take our time off? More research for Project: Time Off found this: “Top reasons workers say they leave vacation unused are fear of returning to a mountain of work (40%) and the belief that nobody else can do their job (35%). The effects of a tough economy still linger: one-third (33%) of employees say they cannot afford to use their time off and nearly a quarter (22%) of workers say that they do not want to be seen as replaceable. Roughly three-in-ten (28%) employees do not use all their time off, because they believe it will show greater dedication to their company and their job.”

Can all those fears be ignored? It’s your call. But know the evidence is just as plain that employees who take their vacations are healthier, have higher job satisfaction and just may be more productive.

This article is commentary by an independent contributor. At the time of publication, the author held TK positions in the stocks mentioned.