The prevalence of obesity and extreme obesity among young children may have begun to decline, according to researchers from the Centers for Disease Control and Prevention.

"To our knowledge, this is the first national study to show that the prevalence of obesity and extreme obesity among young U.S. children may have begun to decline," the authors concluded in a research letter published in the Journal of the American Medical Association. "The results of this study indicate modest recent progress of obesity prevention among young children. These findings may have important health implications because of the lifelong health risks of obesity and extreme obesity in early childhood."

In 1998, the obesity rate for U.S. children ages 2 to 4 was 13%, and the rate of extreme obesity was 1.75%. The obesity rate for children in this age group increased to a high of almost 15.4% in 2004, while the extreme-obesity rate reached highs of more than 2.2% in 2003 and 2004. For 2010, the rates had decreased to about 14.9% and 2.1% respectively. Obesity was defined as a body mass index in the 95th percentile for the child's weight and sex, and extreme obesity as 120% of the 95th percentile.

The researchers compared body mass index data from between 1998 through 2010 that was collected as part of the Pediatric Nutrition Surveillance System. The data includes information on almost 50% of children eligible for federal maternal and child health and nutrition programs, according to the letter. In all, the analysis covered 26.7 million children ages 2 to 4 in 30 states and Washington, D.C.