Worried about overindulging this holiday season? Give yourself a special gift: sleep.

Despite the temptation to have too much of everything during this hectic season, studies now point to the ill effects of missing just a few hours of sleep -- from increased appetite and obesity to a greater risk of high blood pressure and diabetes.

"So many people could benefit from more sleep," notes James Gangwisch, a Columbia University researcher and co-author of a new report on missed sleep. "A lot of people don't even realize that they are sleep-deprived."

Just look at the numbers: In 1910, Americans, who didn't have television, computers and video games to distract them, slept an average of nine hours per night, according to a report in the December issue of the journal Sleep. Based on a 2003 survey by the National Sleep Foundation, adults now average seven hours of sleep nightly, yet about a third sleep six hours or less, according to the National Health and Nutrition Examination Survey (NHANES), a large, federally funded project.

Experts say you should get seven to nine hours of sleep each night.

The effects of too little sleep go far beyond feeling tired and cranky. Skipping sleep fuels appetite, particularly for the kind of comfort food that is high in calories. Small wonder, then, that sleep deprivation is emerging as a key risk factor for obesity and Type 2 diabetes.

In fact, when Gangwisch and his colleagues analyzed the NHANES records of nearly 9,000 adults, age 32 to 86, they found that short sleepers -- that is, those who sleep five hours or less per night -- were nearly twice as likely to develop Type 2 diabetes as those who slept seven or more hours nightly.

Other research, also by Gangwisch, suggests that short sleepers are twice as likely to be obese as people who get enough sleep nightly.

With that knowledge, welcome to the seventh annual Lean Plate Club Holiday Challenge. This marks Week Five of the challenge, which is not about dieting but rather about helping you maintain your weight from Thanksgiving to New Year's Day. It's never too late to join the challenge. Just keep the numbers on the bathroom scale steady from now until 2008 begins.

It's easy to make sleep a low priority during the holidays, when schedules get stretched to the limit by parties, shopping, cooking, travel and the more mundane end-of-year activities, from submitting health insurance reports to filling out expense-account claims.

Yet just an hour less of sleep per night can wreak havoc, as a 2000 study by University of Chicago researchers shows. Sleep researcher Eve Van Cauter and her colleagues had healthy, young adults skip an hour of sleep for six nights. Their hunger increased and blood-sugar levels soared, putting them in a pre-diabetic state that resembled conditions of people decades older. The effects were reversed with a return to normal sleep.

Other studies show that missing sleep cuts leptin levels, a hormone that controls satiety and signals the brain that more food is not needed. "When leptin levels are low," Van Cauter notes, "it tells the brain that we need more calories, and hunger is stimulated." That's why skipping sleep "is highly likely to promote hunger and overeating," Van Cauter says.

Try being more active

Can't find more time to sleep? Then try to be more physically active. Here's why: Exercise reduces the effects of sleep deprivation on insulin resistance -- a key step toward developing Type 2 diabetes. Being more active also helps improve sleep quality.

That's why this week's Holiday Challenge activity goal is to get 30 minutes of exercise daily. You can do that by taking six walks of five minutes each or three, 10-minute walks. Or you can do it all at once. Whatever works for you.

This week's food goal is to swap good fats for bad. So choose foods with healthy mono-unsaturated and polyunsaturated oil, such as olive, canola and safflower oils; as well as omega-3 fatty acids found in avocados, fish, healthy margarine and nuts, and stearic acid, found in dark chocolate. Find a full list of goals, tips and tools to help with your efforts at www.leanplateclub.com/holidaychallenge.

At this time of the year, naps may also help, although the research is less clear on their benefits. If you do nap, try to get some winks at about 3 p.m., a time that Gangwisch says appears to be optimum for the body.

As he notes, getting enough sleep "gives more energy, makes you more creative and helps you feel better. If we put sleep higher on our priority list, we can have more energy to devote to the things that are important in our lives."

You can subscribe to the free Lean Plate Club e-mail newsletter at www.leanplateclub.com. Sally Squires is a writer for the Washington Post.