It's no secret that we all could use a vacation from time to time. Research has proven that "long periods of work without vacation can lead to reduced productivity, diminished creativity, and strained relationships," The Wall Street Journal reports. There are also repercussions to our health. The stress of work has been found to increase cardiovascular risks and aggravate existing conditions.

Despite the benefits of vacations, the United States is one of the few developed countries "that does not require employers to provide paid vacation time," the WSJ notes. However, that trend may be changing. Companies such as Evernote, Netflix, and LinkedIn, are offering employees either flexible or discretionary paid time off. Hewlett-Packard and Sun Microsystems have sent staff home on holidays such as July 4. Charles Schwab, Motorola, and Bridgestone have also forced employees to take certain days off throughout the year.

While these "forced" vacations may be in part to rejuvenate employees, it's also a way to cut down on costs. And while that may be beneficial for the bottom line, are CEOs practicing what they preach?

CEOs, just like any other American worker, need vacation time to unplug, too. It will help inspire and motivate you, as well as help you gain new perspectives and become stronger at task management. But how much vacation time should you take?

Back in the '80s, the average CEO took approximately six days off during the summer, specifically between July 4 and Labor Day. Today, however, the answer isn't as clear. There are a number of variables that can determine the amount of vacation time a CEO can take. Factors like the size of the company, the quality of the executives and upper management, and the challenges facing the company need to be considered before making any vacation plans.

Even if you can't get away for an extended period of time, CEOs shouldn't save up vacation days. Simply unplugging from work on your next business trip could be enough to give you a little charge. As Phil Libin, CEO of Evernote, told PC Magazine:

"I travel a lot. I'm always flying somewhere. I used to, like everyone else, work on airplanes and use that time to catch up on things. Then I stopped. I basically said, 'When I'm on a plane, I won't work. I'll read. I'll play video games. I'll watch TV. I'll watch movies.' And it makes me look forward to flying. I have a 14-hour flight to China coming up and I'm excited about it! I'm going to have 14 hours when I don't have to do anything!"

Nancy Schlichting, CEO of Detroit-based Henry Ford Health System, however, has a different opinion. "Vacation days are intended to reward seniority in the organization, which is why employees get more as they move up." She adds, "I worry about the people who say they can't take a vacation. Why can't they? You start to worry that they aren't leaving work because they have something to protect, as opposed to feeling good about taking time off. The way I look at it: For executives, if they're doing their job really well, they should be able to take time off."

Since there isn't just one finite answer, here's how six powerful executives feel about appropriate vacation time.

Reed Hastings, Netflix CEO

Hastings has publicly announced that he takes six weeks of vacation a year because it's important for work-life balance. He has also said, "It is helpful. You often do your best thinking when you're off hiking in some mountain or something. You get a different perspective on things."

Sheryl Sandberg, Facebook COO

Not only is Sandberg the COO of Facebook, she's also an author. When working on Lean In, she was asked how she was able to balance writing, her job at Facebook, and her personal life. Sandberg claimed it was possible because she used all of her vacation days.

Richard Branson, Founder of the Virgin Group

The eccentric billionaire has been known to take lengthy vacations either traveling the world or relaxing at his home on Necker Island. Branson has said:

"Maintaining focus on having fun isn't just about rest and recuperation: When you go on vacation, your routine is interrupted; the places you go and the new people you meet can inspire you in unexpected ways. As an entrepreneur or business leader, if you didn't come back from your vacation with some ideas about how to shake things up, it's time to consider making some changes.

"I make sure that I disconnect by leaving my smartphone at home or in the hotel room for as long as possible--days, if I can--and bringing a notepad and pen with me instead. Freed from the daily stresses of my working life, I find that I am more likely to have new insights into old problems and other flashes of inspiration."

Because Branson enjoy vacations so much, he's even jumped on board with the idea of providing unlimited vacation time to his employees.

John Donahoe, eBay CEO

In a LinkedIn post from 2013, the eBay CEO advocates for taking a thinking day approximately every three months. For Donahoe, he'll "hide away in an empty office, stand in front of a whiteboard (and it must be a whiteboard), and map out what is going on in the external environment and what I see as the company's most pressing issues in the coming period. I think about what I have learned, which areas require my attention, and what changes I need to make--and remind myself not to worry about events over which I have no control."

However, he also states that there is "still no substitute for taking a legitimate vacation." For the last 28 years, Donahoe and his family vacation at a Cape Cod beach house, where he tries to "completely disconnect for two weeks."

Marissa Mayer, Yahoo CEO

Since taking over as CEO at Yahoo, Mayer has been one busy executive. According to Fortune, she claims that in an average week, "she has about 70 meetings scheduled, taking up 10 or 11 hours a day," on top of managing the company. However, she hasn't gotten overwhelmed during her time as CEO. As she told Fortune, "I pace myself by taking a week-long vacation every four months."

Tony Schwartz, The Energy Project CEO

The founder and CEO of the Energy Project, as well as author of Be Excellent At Anything, Schwartz believes in taking vacations that last longer than a week. But that's not at all. Schwartz is also a fan completely disconnecting. Without distractions, he is able to focus on reading, take tennis lessons, and enjoy himself. I define this as structuring your flexible work life.

As he told Harvard Business Review, "By the end of nine days, I felt empowered and enriched. With my brain quieter, I was able to take back control of my attention. In the process, I rediscovered some deeper part of myself."

Are you a CEO? If so, how many days you take off every year?