The idea that people need less sleep as they get older is a myth, according to a study showing that age bears no relation to how much sleep is necessary to function properly the next day.

What does change with age is the tendency to wake up in the middle of the night. But although disturbed sleep is more common as people age, it affects older people's brain functioning less than it does that of younger people, scientists found.

"What breaks down as we age is not the need for sleep but the ability to sleep in one chunk," said Sean Drummond, associate professor of psychiatry at the University of California.

"For older adults, the more sleep last night, the more efficient brain function is today," he told the American Association for the Advancement of Science in San Diego. "In young adults what is important is consolidating it into one, solid chunk."