"A new and growing body of multidisciplinary research shows that strategic renewal — including daytime workouts, short afternoon naps, longer sleep hours, more time away from the office and longer, more frequent vacations — boosts productivity, job performance and, of course, health.

Spending more hours at work often leads to less time for sleep and insufficient sleep takes a substantial toll on performance. In a study of nearly 400 employees, published last year, researchers found that sleeping too little — defined as less than six hours each night — was one of the best predictors of on-the-job burn-out. A recent Harvard study estimated that sleep deprivation costs American companies $63.2 billion a year in lost productivity.

The Stanford researcher Cheri D. Mah found that when she got male basketball players to sleep 10 hours a night, their performances in practice dramatically improved: free-throw and three-point shooting each increased by an average of 9 percent.

Daytime naps have a similar effect on performance. When night shift air traffic controllers were given 40 minutes to nap — and slept an average of 19 minutes — they performed much better on tests that measured vigilance and reaction time.

Longer naps have an even more profound impact than shorter ones. Sara C. Mednick, a sleep researcher at the University of California, Riverside, found that a 60- to 90-minute nap improved memory test results as fully as did eight hours of sleep.

MORE vacations are similarly beneficial. In 2006, the accounting firm Ernst & Young did an internal study of its employees and found that for each additional 10 hours of vacation employees took, their year-end performance ratings from supervisors (on a scale of one to five) improved by 8 percent. Frequent vacationers were also significantly less likely to leave the firm."

-Tony Schwartz for The New York Times