Originally published by 2 Minute Medicine® (view original article). Reused on AccessMedicine with permission.

1. Heritability and shared environmental factors account for BMI variation in sibling pairs during middle childhood, whereas non-shared environmental factors account for variation in adolescence.

Evidence Rating Level: 2 (Good)

In the United States, childhood obesity is a widespread public health problem, estimated to affect 13% of 2-5 year olds and 20.6% of 12-19 year olds, with cases carrying on into adulthood in 90% of teens. The factors that predispose children to obesity can be genetic or environmental. Previous twin and family studies have provided insight on how genetic and environmental factors influence obesity risk: However, they’ve shown mixed results regarding the relative contributions of genetics and environment, and tended to be limited in their generalizability, such as by focusing on a specific age. Therefore, this current study adds on to previous research by implementing an adoption design, examining biological siblings raised together, raised apart, or raised with non-biological siblings. The sample consisted of 897 children taken from the Early Growth and Development Study, and the Early Parenting of Children study. The measures were BMI, home type (adoptive or birth homes), and genetic relatedness among sibling pairs. For environmental factors, a common environment referred to factors shared comparably by all siblings in a household, whereas a unique environment referred to factors that disproportionately affected siblings in a household. The results showed that the factors influencing BMI vary depending on age. In adolescent sibling pairs, home type was the strongest predictor, with those in a birth home having a 14% higher BMI than an adoptive home (p < 0.001). In middle childhood pairs, genetic heritability accounted for 63% of the variation in BMI (SE = 0.11; p = 0.008), common environment accounted for 31% (SE = 0.10; p < 0.001), and a unique environment accounted for 6%. In adolescent pairs and siblings that spanned the two age groups, heritability and common environment influences were not found to contribute significantly to BMI variation, suggesting that unique environmental factors accounted for most of the variation. Through this design, the relative contributions of genetics and environmental factors for child BMI were estimated. These results could have implications for future interventions that target shared environmental factors in a household during middle childhood, to reduce the risk of obesity.

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