Washington ? Chronic sleeping problems afflict as many as 70 million Americans, costing the nation 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.

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

The institute’s study 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.