"Obesity and extreme obesity in childhood, which are more prevalent among minority and low-income families, have been associated with other cardiovascular risk factors, increased health care costs, and premature death. Obesity and extreme obesity during early childhood are likely to continue into adulthood. Understanding trends in extreme obesity is important because the prevalence of cardiovascular risk factors increases with severity of childhood obesity," writes Liping Pan, M.D., M.P.H., of the Centers for Disease Control and Prevention, Atlanta, and colleagues. National trends in extreme obesity among young children living in low-income families have not been known.

As reported in a Research Letter, the authors analyzed data from the Pediatric Nutrition Surveillance System (PedNSS), which includes almost 50 percent of children eligible for federally funded maternal and child health and nutrition programs. The analysis for this study included 26.7 million children ages 2 through 4 years from 30 states and the District of Columbia that consistently reported data to PedNSS from 1998 through 2010. One routine clinic visit with demographic information and measured height and weight was randomly selected for each child. Obesity (body mass index [BMI] 95th percentile or greater for age and sex) and extreme obesity (BMI 120 percent or greater of the 95th percentile) were defined according to the 2000 CDC growth charts.

The 2010 study population was slightly younger and had proportionally more Hispanics and fewer non-Hispanic whites and blacks compared with the 1998 population. The researchers found that the prevalence of obesity increased from 13.05 percent in 1998 to 15.21 percent in 2003. The prevalence of extreme obesity increased from 1.75 percent in 1998 to 2.22 percent in 2003. However, the prevalence of obesity decreased slightly to 14.94 percent in 2010; and the prevalence of extreme obesity decreased to 2.07 percent in 2010.

"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 write. "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."