Drop in childhood obesity cannot be explained by health behaviors

While a reported drop in obesity rates among U.S. children has been heralded as positive news, more work must be done to understand exactly why that drop occurred, according to researchers at Rice and Temple universities.

A 2014 study by the Centers for Disease Control and Prevention (CDC) showed a decline in the prevalence of obesity among 2- to 5-year-olds between 2003-2004 (a 13 percent child obesity rate) and 2011-2012 (a 7 percent child obesity rate); however, the study did not identify the health and demographic factors linked to the decline. Rice and Temple researchers replicated the CDC's study with 1,900 children between the ages of 2 and 5 in an attempt to explain the changes. Their discovery: The 6 percent drop in childhood obesity cannot be explained by changes in maternal or child health behaviors such as smoking cessation, breast-feeding or physical activity.

"Even though maternal and child health behaviors changed in important ways, none of these changes contributed to the decline in obesity overall or for boys or girls," said the study's lead author, Ashley Kranjac, a postdoctoral research fellow in Rice's Department of Sociology and the Kinder Institute Urban Health Program, and co-author Robert Wagmiller, an associate professor of sociology at Temple. Their research paper, "Association Between Age and Obesity Over Time,"appeared in the April edition of Pediatrics.

The obesity rate was lower in 2011-2012, when older children between the ages of 2 and 5 were no more likely to be obese than the younger children in this age range, compared with 2003-2004, when older children in this age group were more likely to be obese than younger children between the ages of 2 and 5.

"We show that in 2011-2012 a smaller proportion of children lived in low-income households, had mothers who smoked during pregnancy, had mothers who did not breast-feed, had high daily energy intake, spent significant time involved in sedentary activities and frequently ate out," the authors said. "And we found that a higher proportion of children engaged in physical activities for significant amounts of time. Despite these differences, the main reason for the decline in the obesity rate is that children surveyed in 2003-2004 were more likely to be obese as older children. However, this was not true for children surveyed in 2011-2012."

Kranjac and Wagmiller said their research shows that more must be done to understand the factors that influence childhood obesity.

"If the association between age and obesity observed from 2011 to 2012 persists for subsequent groups of children, the obesity rate for young children will remain at or near the lower rate observed at this time," Kranjac said. "Even more encouraging, if this weakened association between age and obesity persists as these children advance into middle and late childhood, significant reductions in obesity in later childhood can be expected, as well as significant declines in the overall rate of childhood obesity over time."