Obesity: The Sibling Relationship

obesityA new study has found that the relationship between siblings is a stronger indicator of childhood obesity than that of parent and child.  The study, from Cornell University, Massachusetts General Hospital and Duke University looked specifically at how having an obese sibling affects a child’s risk of being overweight. Results of the study were published in the American Journal of Preventive Medicine in October.

Other studies have established that there is a strong tendency toward heaviness in children with overweight parents. The new study looked at data on both parent-child and sibling relationships. Surveying 10,244 American households, the study found that the obesity status of an older sibling was more strongly associated with the younger child’s tendency toward being overweight than was the parents’ weight. The study also included gender differences, finding that a younger sibling would be influenced more if the older sibling was of the same sex. Girls are less likely to be obese than boys.

In a two-child household with at least one overweight parent, older children are 2.3 times more likely to be obese. That number increases to 5.4 times for those with younger siblings who are overweight. In the same household size, parental heaviness is not related to the risk for the younger sibling, but having an obese older sibling carries a risk of 5.6 times higher.

Study authors say the sibling obesity relationship is 11.4 times more for youngest boys in two-child families where there is a male older sibling. Younger boys are 6.6 times more likely to be overweight if the elder sibling is a girl. For families with two girls, the younger child is 8.6 times more likely to be obese, but is not significantly affected if the older child is a boy.

According to the investigation, only children are more likely to eat fast food and less likely to get exercise through physical activity than children with brothers and sisters. The data, however, also showed that the obesity risk for the younger child was actually increased by having a highly active older sibling.

Mark C. Pachucki, PhD, from Massachusetts General Hospital and the lead investigator on the study, said the associations found in the study were independent of demographic and socioeconomic attributes, or overall health status or behaviors. He said that the findings were consistent with previous research that showed that siblings tend to have similar physical activity levels and eat alike.

Previous studies have also shown strong connections between parent obesity and overweight children even in adoptive families where children were not biologically related to their parents. This can reflect dietary habits, nutritional levels, and learned patterns of physical activity.

Study authors acknowledge that since the research was based on “a snapshot of one point in time,” they cannot claim that siblings actually cause each other’s weight gain. Additionally, they looked only at one and two-child families with two parents. Although more research is needed on family weight problems, the authors say that new study offers key data on sibling relationships that can be used in the fight against childhood obesity.

By Beth A. Balen

Medical Press
Medical Daily
University of Michigan

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