There's good news and bad news about your upcoming vacation. It comes from a pair of recent studies of the Dutch, who ought to know a thing or two about the subject. Dutch workers on average are entitled to 25 days off a year and use 23 of them, according to a survey by online travel broker Expedia.com; Americans on average are offered 12 days off and take only nine.

The bad news is that, although your vacation will likely make you happier and probably even healthier, those effects won't last long.

The good news is that the benefits of your vacation start sooner than you might think. In fact, you re likely already happier than usual, unlike co-workers who haven't planned a break.

Vacation science is almost nonexistent. Despite vacations being a sizable contributor to the world economy Americans alone will spend $76 billion on summer vacations this year, up $7 billion from last year, according to a survey by travel insurer Mondial Assistance USA there's relatively little research available that measures vacation effects.

In a study published in the August issue of Work & Stress, an academic journal, authors cited the vacation knowledge gap as motivation for their research. They surveyed 96 Dutch workers over a seven-week period beginning two weeks before their planned vacations. Workers were asked throughout the period about wellness factors including their health status, mood, level of tension and energy and satisfaction. Participants reported improvements in each of these measures during their vacations, as expected. However, just one week after returning to work, their self-reported measures of wellness had returned to pre-vacation levels.

That suggests the benefits of vacations are real but short-lived. What the study results don't show, and what the authors suggest future studies look at, is how changes in vacation time affect the duration of benefits upon return. For example, if a worker has 10 vacation days to use during summer, does he capture greater total happiness by using them all at once on an extended getaway, or by taking Fridays off all summer long?

Another study, published in the March issue of Applied Research in Quality of Life, looked at survey results from more than 1,500 Netherlanders, almost 1,000 of whom had gone on vacations. Like the aforementioned study, this one found little difference between the happiness of vacationers and non-vacationers once the vacations had ended. Time off refreshed workers, but the effects were far from lasting. However, the study also showed a marked increase in the self-reported happiness of vacationers in the weeks leading up to their trips.

As the English poet and quote-machine Samuel Johnson said, "Such is the state of life that none are happy but by the anticipation of change. The change itself is nothing; when we have made it the next wish is to change again."

The implications for workers are clear. Plan vacations well in advance. Doing so can save money, but more important, it prolongs the anticipatory phase, thereby increasing total happiness. How best to handle the dip in happiness upon returning to work? Simple: Start planning your next vacation right away.