When was the last time you took a vacation? For me, it was October 2013 when I spent a week in a Cape Cod cottage staring out at the autumn ocean and slowly recovering from a bad case of burnout. In other words, it's been too long.

If that's true for you too-or even if you haven't had a vacation in six months or more-you absolutely must take one this summer. Not only will you be better at your job, more engaged at work, and better connected with your family-it may well extend your life.

That news comes from John de Graaf, president and co-founder of Take Back Your Time, a non-profit dedicated to curing the epidemic of "vacation deprivation" in the United States. De Graaf and Take Back Your Time are as serious as you can be on the subject of vacations-so much so that they are hosting a Vacation Commitment Summit in New York City next month so that business leaders and academics can discuss the problem.

And it is a problem. While the United States is among the richest nations on earth, we're poverty-stricken when it comes to leisure time. Even though Americans are offered less vacation time than nationals of most other countries-in many countries a 20 or more vacation days per year are mandated by law-we don't even use the little we get. American employees failed to take a total of 429 million days off that they were entitled to last year, and more than a third of us never take vacations at all.

This is especially true for the lowest-paid workers, who may receive no vacation time, but also for entrepreneurs and small business owners, who only get vacation time if we give it to ourselves. But taking vacations should be non-negotiable for everyone, de Graaf says. Here's why:

1. You'll be more productive.

There's ample evidence that people who take regular vacations are both more engaged at work and get more done. This is why some companies believe it's smart to actually pay employees to take a vacation every year. According to Take Back Your Time's vacation survey, those who take yearly vacations report being more efficient at work than those who don't.

2. You'll enjoy your work.

And if you don't take vacations, you likely won't. Only 27 percent of survey respondents who don't take vacations reported being satisfied at work, compared with 71 percent of regular vacationers.

3. You'll be easier to work with.

You don't need statistics to tell you that a burned-out person who's unhappy at work is less fun to be around than a relaxed, happy, enthusiastic one. Sure enough, the Take Back Your Time survey confirms that those who take few vacations are harder to work with than those who vacation annually.

4. You'll set a valuable example.

If you're a manager or small business owner, you'll have a more pleasant workplace if your co-workers and employees are happy and rested rather than burned out and irritable. Unfortunately, de Graaf reports that many American employees don't take vacations because they're afraid to. "Many businesses really want workers to take the time off but the workers either believe that their job security is based on being at work all the time or that so much work will pile up while they are gone that they will be so stressed when they come back to work the time off won't be worth it," he says.

Part of the problem, he adds, is our "cultural attitude that reveres production and economic growth above other things like leisure and health." As the boss, the most powerful way you can counter the perception that taking a vacation isn't OK is by taking one yourself.

5. Your home life will improve.

It seems pretty self-evident that taking a vacation is good for your work-life balance, and will strengthen relationships that may be under pressure if you have a heavy work schedule, as so many entrepreneurs do. The survey confirms that 86 percent of annual vacationers feel a strong family bond, compared with 69 percent of non-vacationers. And 80 percent of vacationers reported increased romance in their relationships as well.

6. You'll live longer.

Taking regular vacations will help you avoid a whole list of medical issues, including depression, according to Leigh Vinocur, MD, who has studied the health effects of vacations. It's one reason more than half of those who take annual vacations rate their own health as good or very good. Not only that, research shows that men who take vacations more than once a year cut their risk of heart disease by 30 percent, and women who take vacations more than once a year cut their risk by 50 percent.

7. You'll be happier.

For de Graaf, this is the bottom line. "My strongest memories of childhood come from the two-week vacations my parents took me on-the Seattle World's Fair, National Parks, Disneyland, a little resort in Clear Lake in California. I feel like I remember every detail," he explains when I ask why he cares so much about people taking vacations.

When he began researching the topic, he learned that he is not alone, and that many people's strongest childhood memories come from vacation times. Then, he says, "I got involved in the international happiness movement and learned that psychologists have discovered that experiences like vacations bring more long-lasting satisfaction than material goods. And that people who vacation are much more likely to say they are happy than those who don't."

And really, whatever our business, however hard we do or don't work, isn't that ultimately all any of us wants-to be happier? So we should all make sure to take vacations because-besides all their other benefits-they've been scientifically proven to do just that.