How much sleep we need is largely a mystery, and sleep seems tougher to come by as we age. Many studies — often funded by the pharmaceutical industry — have suggested that we're all sleep-deprived zombies, risking our health for lack of shut-eye.

But new research in the U.K. confirms previous indications that older people need less sleep. It also suggests that variations in sleep hours needed are normal and healthy — so long as one is not overly sleepy during the day.

"Healthy aging appears to be associated with reductions in the sleep duration and depth required to maintain daytime alertness," the scientists said in a statement.

Still, researchers warn that many people in modern society suffer from sleep deprivation, and that it can lead to plenty of woes from accidents on the job to higher risk of falls and even death in elderly people.