Recent studies have shown that after decades of rising youth obesity rates, the numbers seem to be leveling off or declining, according to a report in the journal Pediatrics. However, the slight decline may depend on the income level of a child's household.

Researchers who were studying Boston-area obesity rates and how they compare to the national average found that after holding steady between 1999 and 2003, the obesity rate began to fall after 2004 for children who were patients at Boston-area pediatric offices. By 2008, just under 9 percent of boys were obese, compared with almost 11 percent between 1999 and 2004. Among girls, the obesity rate declined from over 8 percent to just over 6 percent.

Two national databases noted a similar trend nationwide, the researchers found. Just over 10 percent of 2- to 6-year-olds in the United States were obese in 2008, down from 14 percent in 2004. However, the rate among children younger than 2 remained at 9.5 percent, the study reported.

The researchers saw little change in the obesity rate of lower-income children in the Boston area who were on Medicaid—11.5 percent were obese in 2008, down from just over 12 percent in 2004.

A national database that tracks mostly low-income children throughout the United States showed that obesity rates remained stable between 2004 and 2008 at almost 15 percent among low-income children between the ages of 2 and 6.

Greater awareness of the problem and pediatric screening for obesity could be playing a role in the decline, Dr. Xiaozhong Wen, of Harvard Medical School and the Harvard Pilgrim Health Care Institute in Boston, told Reuters Health.

Wen said further study is needed to determine why the obesity rate among higher-income children seems to be declining while the rate for lower-income children is not.