Study: Siblings are more likely than parents to influence child obesity

A new study released Tuesday found that children are more than twice as likely to be obese if they have an obese sibling, as opposed to if they have an obese parent. If the sibling is of the same gender, the risk is even stronger.

Researchers at the Mongan Institute for Health Policy at Massachusetts General Hospital looked at data from roughly 2,000 respondents to the Family Health Habits Survey, a nationwide survey of parents that looks at health between family members. The study, which will be published in the October issue of the American Journal of Preventive Medicine, found that younger children turn to older siblings as examples, whether good or bad.

"Younger children look up to their big brother or sister for behavioral cues, often seeking their approval," Dr. Mark Pachucki, the author of the study, said in a statement. "Siblings may spend more time each other than with their parents, often eating and playing sports together."

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In one-child families, having an obese parent more than doubled the risk the child would be obese, though high levels of physical activity lowered the child's risk. But for households with two children, the obese parent risk factor was true for the older child, but not the younger sibling.

Having an obese older sibling created a risk more than five times greater than a non-obese sibling, but an obese parent didn't affect the younger sibling's risk. For siblings of the same gender, the results were even more alarming: The older sibling created an obesity risk 8.6 times greater for girls and 11.4 times greater for boys.

"While this study doesn't allow us to say that one sibling's obesity directly influences the other's, the associations we found are pretty interesting," Pachucki said. "Now we need to try and replicate these analyses with other national datasets and think through how to use this information to improve family-based health intervention models."