Overweight 5-year-olds are four times as likely as normal-weight children to become obese as adults, according to a study published.

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The study, published in the New England Journal of Medicine, followed 7,738 participants who were in kindergarten in 1998 in the United States. They found that the incidence of obesity were 31.8% in overweight 5-year-olds vs. 7.9% in normal-weight 5-year-olds. Children who began school overweight were more likely to become obese than those who did not.

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“Although trends in the prevalence of obesity are documented, surprisingly little is known about the incidence of childhood obesity. Examining incidence may provide insights into the nature of the epidemic, the critically vulnerable ages, and the groups at greatest risk for obesity,” according to the study. Incidence of obesity is when a child develops obesity when the child was not previously obese.

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Researchers analyzed data from the Early Childhood Longitudinal Study, Kindergarten Class of 1998 – 1999. The National Center for Education Statistics (NCES) selected a nationally representative sample by using multistage probability sampling. The researchers calculated each child’s BMI.

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The study found that race played a factor in the incidence of obesity. Hispanic children were more likely to become obese than non-Hispanic white children at all ages. Starting in the third grade, this was also true for non-Hispanic black children. 

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The study also linked socioeconomic status and overweight kindergarteners with the incidence of obesity. Overweight children from the two highest socioeconomic groups had five times the risk of becoming obese compared to normal-weight children of the same demographic group.  

 

The largest factor in difference of risk was found in children born with an above average birth weight but had become overweight by the age of five. They were 5.1 times at risk of incidence obesity. 

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More than one-third (36.5%) of U.S adults are obese and two-thirds (70%) of U.S adults are either overweight or obese, according to the CDC. The estimated annual medical cost of obesity in the U.S was $147 billion in 2008.

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The study's authors write that their findings highlight the importance of further research to understand the factors associated with the development of overweight.