Scientists can't say exactly how much sleep each person needs, but there are some guidelines. And you should know that serious lack of sleep less than six or seven hours a night has been associated with increased risks of high blood pressure, hypertension, obesity, diabetes and cancer.

But much about sleep's role in health, and the how much sleep each person needs, remains a mystery. Some studies have suggested that older people need less sleep. Research reported in the journal Current Biology in 2008 found that when asked to stay in bed for 16 hours in the dark each day for several days, younger people participants slept 9 hours on average while older people got 7.5 hours of shut-eye. And a study Feb. 1, 2010 in the journal Sleep concluded older people need less sleep.

Some general guidelines from the Mayo Clinic on how much sleep is needed:

  • Preschoolers: 11 hours
  • School-age children: 10 hours
  • Teens: 9 hours
  • Adults: 7-8 hours
  • Seniors: 7-8 hours

If you have trouble falling asleep, there are a host of tips to try, including:

  • Exercise
    Avoid caffeine and alcohol.
    Set a regular bedtime and place (ideally a bedroom) and stick to it.

Here are more sleep tips.

Experts generally agree that quality sleep is important, naps are good (though they can make night-time sleep harder to achieve), and that some people simply need less sleep.