Prevention policies may have put the brakes on obesity among preschoolers in New York and Los Angeles, government researchers found.

By 2011, the prevalence of obesity among 3- and 4-year-olds in these cities was generally on the decline, although it had followed different tracks over the last decade, Jackson Sekhobo, PhD, of the New York State Department of Health, and colleagues reported in the Jan. 18 issue of the CDC'sMorbidity & Mortality Weekly Report.

In New York, preschooler obesity prevalence generally fell between 2003 and 2011, while in Los Angeles, it rose and then finally took a downturn around 2008-2009, they reported.

Overall, prevalence of obesity among these age groups was falling in recent years:

The data are "consistent with national data indicating that increases in obesity prevalence among preschool-age and school-age children have leveled off," Sekhobo and colleagues wrote.

But the differences between cities may be explained by variations in the uptake of obesity prevention policies, they speculated.

For their study, Sekhobo and colleagues looked at data from the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) in New York City and Los Angeles between 2003 and 2011. Depending on the year, the total number of enrolled children ranged from 53,000 to 67,000 in New York and from 147,000 to 149,000 in Los Angeles.

During that time, obesity among preschool children in New York fell for blacks, whites, and Hispanics, but increased among Asians, they reported.

In Los Angeles, obesity prevalence fell among Asians over the study period -- but it initially rose among whites, blacks, and Hispanics, and was followed by a decline.

Hispanic children had highest prevalence of obesity in both cities, at 19.1% in New York and 21.7% in Los Angeles in 2011 -- a drop for New York city kids, at 24% in 2003, but a rise for Los Angeles kids, who were at 17.8% at that time point.

Over the course of the study, obesity prevalence started out lower in Los Angeles, but that changed in 2005 and remained greater in the California city through the end of the study, the researchers said. Obesity prevalence finally started to fall for Los Angeles preschoolers between 2008 and 2009, they said.

The differences between the two cities may be due to sociodemographics, variations in the built environment, or to differences in ethnic groups.

But it may also have something to do with differing strategies when it comes to obesity prevention policies, the researchers said.

For instance, New York had over the last decade implemented many interventions to address childhood obesity, while similar strategies started to be implemented in Los Angeles at a later time.

"It's possible that interventions and policies aimed at prevention of childhood obesity might have taken effect earlier in New York than in Los Angeles," they wrote.

The study was limited because data come from participants in WIC and may not be generalizable outside of that population.