Adults should strive for eight hours of sleep, children and teens for nine hours. Only 26 percent reported getting the necessary eight hours, down from 35 percent.

The result: more illnesses, a weakened immune system, impaired judgment — not to mention crankiness, depression and other ailments. Recent studies have linked inadequate sleep with obesity, heart disease, high blood pressure and type 2 diabetes.

Here are some tips for a good night's rest:

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Dark is good. Darkest is best. Light signals the brain to wake up. That means your alarm clock flashing those blue digits can jolt you awake long before you are ready. Turn the clock toward the wall or hit the dim switch. "You need darkness, quiet and comfort to sleep — and the need to be safe. If you're not safe with your home or bed partner you won't sleep well," cautions Joyce Walsleben, a sleep specialist with the NYU School of Medicine.[naviga:font face="ZapfDingbats"]4[/naviga:font]

Eat properly. Going to bed overstuffed, especially on carbs and fat, interferes with sleep. Starving yourself also counters a good night's rest. Try a small high-protein bedtime snack, maybe a little cheese or a hard-boiled egg.[naviga:font face="ZapfDingbats"]4[/naviga:font]

A snoring bedmate. Suggest, lovingly of course, that your partner sleep on his or her side. Barring that, opt for comfortable earplugs or consider separate bedrooms.[naviga:font face="ZapfDingbats"]4[/naviga:font]

Keep to a schedule. Body rhythms matter. Try to wake up at the same time every day — even if you go to bed later than usual on a party night. You might get away with sleeping in an extra hour, say on the weekend, but any more than that and you are "jet-lagging" your system.[naviga:font face="ZapfDingbats"]4[/naviga:font]

Go to bed 15 minutes earlier. If you cut 15 minutes off of your activity and go to bed at 11:45 instead of midnight, you net at least an additional one hour of sleep per week.[naviga:font face="ZapfDingbats"]4[/naviga:font]

Nap smart. A short siesta, about 20 to 30 minutes in the early afternoon, can be refreshing. Be careful. Nap too long and you enter REM sleep. You'll wake up groggy and have a hard time falling asleep at bedtime. Napping too late in the afternoon, at 5 p.m. or later, also impacts night sleep.[naviga:font face="ZapfDingbats"]4[/naviga:font]

Keep your feet covered. This widens blood vessels down there, drawing heat from the core to the extremities, which cools you a little, inducing sleep.[naviga:font face="ZapfDingbats"]4[/naviga:font]

Play music that you consider relaxing. Dock your iPod into a speaker system and set its timer so the lullaby can cease once you reach sleep.[naviga:font face="ZapfDingbats"]4[/naviga:font]

Can't sleep? Stay in bed. No, get outta bed. Experts differ on this one. A Duke University expert suggests leaving the bed. Walsleben, however, advises staying in bed. "You'll have more of a chance to fall asleep in a dark room than if you get up to do something else, like getting hooked on the Internet," she said. Both agree that whichever option you settle on, do not turn on any lights.

Sources: Darrel Drobnich, National Sleep Foundation; Joyce Walsleben, NYU School of Medicine; Drs. Dalia Lorenzo and Douglas Wallace, UM/VA Hospital; Prevention magazine; Jose Oliveros, North Shore Medical Center; National Center on Sleep Disorders Research and Institute of Medicine.