Train carriages filled with white-collar workers dozing off on each other's shoulders are one of the most striking sights in Japan.

It's no wonder that a nation notorious for its sluggish economy and apathetic citizenry can't seem to set a course out of the doldrums, because -- according to a global survey on sleep habits -- half the country is blundering through life half asleep.

The study by market research firm ACNielsen, published last month, found that 41 percent of Japanese people manage six hours or less zzzzs per night, making it the most sleep-deprived nation on Earth.

Even the somnolent and slothful authorities have acknowledged the extent of the problem, listing sleep as one of the targets for action under the government's Healthy Japan 21 campaign. In this, it lists "ensuring sufficient sleep" as one of the goals "to ensure the maintenance of mental health."

Sleep deprivation certainly isn't healthy -- it has been used as a torture technique since Roman times -- and prolonged lack of sleep induces psychosis and causes victims to lose their sense of self-identity.

But according to a 1999 study by Penn State's College of Medicine, even one night of disrupted or missed sleep by a healthy person can drastically alter their chemical balance, and also cause daytime sleepiness and fatigue. The research found that interrupted sleep also disrupted immune systems, leading to an increase in the likelihood of infections and disease, and that even such mild sleep deprivation drastically reduced productivity and increased the chances of accidents at home or at work.

According to Yuriko Doi of the National Institute of Public Health, Japan, white-collar workers with poor sleep quality are more likely to take sick leave, suffer from poor physical health and have problems in occupational activities as well as personal relationships.

"The effects on performance are wide-ranging and severe," she says. "In terms of quality of life, poor sleep quality causes all sorts of misery."

After the last 10 years of downsizing, many office workers have to work very late. According to Makoto Uchiyama, director of the National Center of Neurology and Psychiatry, sleep loss is hitting Japan's millions of middle-aged men particularly hard.

"When it comes to relationships at work and at home, sleep loss seems to be having a devastating effect," he said. "And it is possibly linked to the huge numbers of men driven to suicide in middle age."

Men in their forties and fifties now make up 40 percent of the 35,000 people ending their own lives in Japan every year, and the current upsurge in the suicide rate can be mostly attributed to a massive rise in suicides among this group.

Although the effects of sleep loss on the vast majority of the population are far less dramatic, they have a profound influence on the way the nation operates. One of the most obvious effects is rendering workers less efficient. Perhaps Japan's dozy workforce has something to do with its poor labor-efficiency rating -- it ranks 18th out of the 30 OECD countries.

Yuriko Doi says that although a precise figure has not been calculated, the cost of sleep loss to the Japanese economy could amount to tens of trillions of yen. She cites "Wake Up America," a 1990 study conducted in the United States, which estimated that poor sleep quality cost the world's largest economy $15.9 billion a year. The mind boggles at what it must be costing the world's second-biggest economy every day of every week of every year right now.

It's no secret that in these days of restructuring and downsizing, Japanese office workers are being forced to work inhumanly long hours. Taisuke Aimono, a 28-year-old white-collar worker, said that on weekdays he gets by with as little as four hours sleep a night.

"I finish work after 10 p.m. most week nights," he explained. "After drinks with colleagues, the commute home and a couple of hours winding down in front of the TV, it's 2 a.m. and I have to be up 4 hours later."

But Aimono says that he often feels dozy during the daytime, and most of his colleagues push themselves to the limit. "Everybody in my office looks exhausted all the time," he says. "They're always complaining of being tired and feeling depressed. We all think we're tough, but sooner or later one of us is going to collapse."

Sayuri Tenmizu, a 31-year-old saleswoman, says she knows she should get more sleep, but she can't fit more than six hours into her daily routine. "Magazines say your skin and general health suffer if you don't get enough rest, but I just can't get to bed before 1 in the morning," she says. "I wish I could sleep more, I feel like I'm always half asleep -- like I'm always numbed to life."

Both Tenmizu and Aimono admit that they spend a large portion of their evenings in front of the television, and watching TV may well have something to do with Japan's chronic lack of sleep. According to the annual Eurodata TV Worldwide study published last week, Japanese people spend more time in front of the TV than any other nation, with an average daily viewing time of 5 hours 1 minute.

The health and wealth of the nation is at stake -- and it's high time Japan turned off the TV and went to bed.