Chronic sleeping problems afflict millions, costing billions in medical expenses, accidents and lost productivity, a new study reports.

"Balm of hurt minds" to Shakespeare, sleep seems to be necessary for the nervous system to work properly, and a lack of sleep can hamper the immune system, cause memory impairment and reduce ability to concentrate.

As many as 30 million Americans, more than one in 10, suffer specifically from chronic insomnia, according to the study released Tuesday by the Institute of Medicine, an arm of the National Academy of Sciences.

And other disorders ranging from sleep apnea — breathing interruptions during sleep — to sleepwalking and restless leg syndrome affect millions more, the study found.

Yet medical students get little training in sleep problems and research on the subject is limited, prompting the institute to call for more research and training programs.

"Although sleep research and care for individuals with sleep disorders have expanded over the past several years, we currently don't have the capacity to adequately diagnose and treat all who suffer from these problems," said Harvey Colten, chair of the committee that wrote the report and former vice president and senior associate dean for academic affairs, Columbia University Medical Center.

Dr. Michael Thorpy, director of the Sleep Wake Disorders Center at Montefiore Medical Center in New York, agreed on the need for research and education.

There are some 80 different sleep disorders, he noted, and lots of areas where there is very little research, including important ones like sleepwalking.

Today physicians are far more interested in sleep problems than they were years ago, but there is still a lack of training, and "most medical students are lucky if they get two or three lectures at most on sleep problems," said Thorpy, who was not part of the Institute research team.

The IOM report said that loss of sleep has increased in recent decades due to longer workdays and computer use and television watching taking up more of people's time.

Lack of sleep increases the risk of a variety of health problems, the report said, including diabetes, cardiovascular disease and heart attacks.

It also raises the chances of injury or death due to accidents at work, home or in automobiles.

Studies in the 1990s estimated the cost of medical care for sleep disorders at $15.9 billion, the report said. In addition, it said, fatigue is estimated to cost businesses roughly $150 billion a year in lost productivity and mishaps, and damage from motor vehicle accidents involving tired drivers amounts to at least $48 billion a year.

Just last week the National Sleep Foundation issued a report showing that only 20 percent of the nation's adolescents get the recommended nine hours of sleep every night. As a result about one in four in this age group had dozed off in class and many drove while drowsy and were late for school.