Nearly a third of Americans seem to be ignoring some important signs – or perhaps slept through them. According to the 2008 “Sleep in America” poll, 29 percent of respondents said they fell asleep at work – or at least came close to nodding off – in the past month.

The poll, conducted by the National Sleep Foundation (NSF) in Washington, D.C., revealed not only how drowsy many employees are at work, but that sleepiness causes 12 percent of workers to be late for work and about a fourth to drive drowsy during the work day. Together, these findings point to a less alert and productive employee.

“Even mild sleep loss, losing 40 minutes a day for five to seven days, will degrade performance over time,” says Dr. Greg Belenky, a member of the NSF board of directors. A research professor and director of the Sleep and Performance Research Center at Washington State University in Spokane, Belenky says lack of sleep affects cognitive performance, or those processes involved in thinking and remembering.

The lapses in attention and reduced productivity that result should be a wake-up call for employees and employers. Being out of it because you haven’t slept costs employers in lost productivity and can result in the loss of a promotion or even the job. It also increases the chance of an accident from driving or operating machinery at work and can lead to long-term health consequences.

Studies show that even young, healthy people who restrict sleep over time can experience changes in their bodies that lead to chronic illnesses. Poor sleep habits even affect weight control. It’s all a factor of the body’s regulation of glucose, but simply put, restricted sleep can make a person slowly gain small amounts of weight over time, or at least make it more difficult to take weight off.

Work and sleep are so closely intertwined, however, that the solution is far from simple. Workdays are longer, as is time spent awake at home before and after work. The time is not wasted; it’s spent with family, on household chores, even doing additional work at home. “And you have to factor in commute costs, both in terms of time and money,” Belenky says. The NSF study found the average work commute to be 47 minutes round trip each day. All of this makes finding time for sleep more challenging and stress more likely.

The weekend, however, is not a time to make up for lost sleep or lost productivity, says psychologist Dr. Kenneth Nowack, president of human resources consulting firm Envisia Learning in Santa Monica, Calif. “You wake up lethargic and fatigued and work is just another place you’re going with a lack of energy. It’s your next target,” he says.

Nowack often counsels workers with attitude and performance problems and often finds that adequate rest and sleep are a top issue. “Some people with insomnia and other sleep difficulties need to seek professional assistance,” he says. Even those who don’t have sleep disorders need to understand you can’t make up for sleep deprivation with a few nights of catch-up, Belenky says. The real key is to make sleep a priority. “Don’t have a television in the bedroom,” he says. Late-night television in particular is designed to stimulate, making it tougher to fall asleep. Keep out work materials and computers and make the bedroom about sleep and comfort. Exercise regularly, but finish at least three hours before bedtime if possible.

Caffeine really does work as a pick-me-up at work, but Belenky says a nap is even better. The “siesta culture” is on to something. It may be tough to sneak a nap into your work day, but some employers sanction the idea. “They’d rather have an alert employee for seven hours than one in a daze for eight hours,” he says.