Of the 79 percent of American workers who have access to paid time off for vacations, more than one-third of them don't use it. And 37 percent of the employees who do take vacations take less than a week at a time.

According to 'Overwork in America: When the Way We Work Becomes Too Much,' a study from the Families and Work Institute, employees' reluctance and/or inability to use their vacation time is a symptom of feeling overworked. The study indicates that one-third of all U.S. employees are chronically overworked. This finding has a significant impact on both employers and employees. The study suggests that the more overworked employees are, the more likely they are to make mistakes at work, feel angry at their employers for expecting so much, and resent colleagues who do not work as hard as they do (i.e., colleagues who use all their vacation time).

How can vacations help? A vast majority of employees report feeling more relaxed and more energized when they return from their longest vacations. Employees who take a higher percentage of vacation days just to relax and enjoy themselves, rather than to tend to family responsibilities or personal illness, are significantly less likely to return to work feeling overwhelmed by all they have to do. Of course, those who are most overworked on the job and work frequently during their vacations (14 percent of all employees) are much more likely to be overwhelmed and less likely to feel energized and relaxed when returning to work from their longest vacations. For much of the employee population, however, vacations offer valuable restorative effects. These effects are most significant when employees take longer vacations. The study shows that vacations of seven days or more are associated with better psychological outcomes than shorter vacations.