Recent research analyzed by University of Michigan doctors finds that third graders who got adequate sleep at night, about 9 1/ 2, were less likely to be in the obese weight category by the time they were in the sixth grade.

Lack of sleep in adults results in increased ghrelin, a hormone that stimulates appetite, and decreased leptin, the hormone that promotes fullness. The overall impact of this condition produces increased weight. Tiredness in kids also may lead to less exercise and more munching.

In the study, of the children who got 10 to 12 hours of sleep a night, about 12 percent were obese by sixth grade. Of those who got less than nine hours a night, 22 percent were obese in the sixth grade (Carla Johnson, "Lack of Sleep May Lead to Fatter Kids," Associated Press, Nov. 5, 2007).