MAYBE WE'RE NOT SLEEPING ENOUGH

The research: How much people sleep can affect how much they weigh. A 2007 study of 785 elementary school students conducted by Dr. Julie Lumeng of the University of Michigan found that the less sixth-graders slept, the more likely they were to be overweight. And for every extra hour of sleep they got per night, the risk of being overweight was reduced by 20%. Among third-graders, the less they slept, the more likely they were to be overweight in sixth grade -- every additional hour of sleep reduced the risk by 40%.

A 2006 study of 422 grade-schoolers ages 5 to 10 found the risk of being overweight was 3.5 times higher for children who got fewer than 10 hours of sleep per night than for those who got 12 hours or more. Sleep affected weight more than physical activity and time with computer or TV.

A 2004 study found that after two nights with only four hours of sleep, males in their 20s were very hungry, especially for high-calorie goodies. And studies of people and rats show that sleep deprivation leads to less leptin, a hormone that says "stop stuffing your face," and more ghrelin, one that says "time to chow down."

Americans sleep one to two hours fewer these days than 40 years ago, and young adults are more than twice as likely to get fewer than seven hours of sleep -- 37% did in 2002, versus about 16% in 1960. Cellphones may contribute. In a study presented last month at a meeting of the Associated Professional Sleep Societies, excessive cellphone use in teens increased disrupted sleep, restlessness, stress and fatigue.

Our experts weigh in: "I think this is like a sleeper, pardon the pun," says Dr. Wendy Slusser of UCLA. "It's something you don't really think about." "I think there is something to this one," adds James Hill of the University of Colorado. Adds Susan Roberts of Tufts University, "It's part of the larger issue, that life is so rushed that healthy eating and home-prepared food take a back seat."