Chronic sleep problems afflict 70m Americans

"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 programmes.

"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 Centre.