The association between parental and offspring body mass index may be due to genetic confounding

1. The association between parental body mass index (BMI) and offspring BMI from age 6 months to 8 years may primarily be due to genetic confounding.

Evidence Rating Level: 2 (Good)

Although parental body mass index (BMI) has been associated with offspring adiposity in childhood, the mechanisms behind this relationship remain unclear. This study thus explored whether these associations are due to genetic confounding (inheritance), rather than to a causal effect of parental BMI on offspring obesity traits. This cohort study analyzed data from a prospective study in Norway, which included births between 1999 and 2009 in Norway. The exposures were maternal pre-pregnancy BMI and paternal BMI during pregnancy at baseline (~17 weeks gestation). Offspring outcomes included birth weight and BMI assessed between age 6 months and 8 years, and appetite-related eating behaviour traits assessed at age 8 years. A genetically informed structural equation model (SEM) was used to analyze a population-based sample of twins, siblings and half-siblings, and their children to determine the extent to which associations were due to genetic confounding. Up to 85,866 children (51.3% male) were analyzed, with 50,999 children included in the SEM models. Compared to paternal BMI, higher maternal BMI was more strongly associated with offspring birthweight (β 0.12, 95% CI, 0.12-0.13 vs 0.01, 0.01-0.02). However, this maternal-paternal difference decreased for offspring BMI after birth, with associations becoming similar for offspring BMI at ages 2 to 5 years. Greater maternal and paternal BMI were associated with increased food responsiveness and emotional overeating, and reduced emotional undereating. In SEM analyses, genetic confounding did not explain the association between parental BMI and offspring birthweight; however, it did explain the majority of the association with offspring BMI from 6 months to 8 years. For 8-year BMI, genetic confounding explained 79% (95% CI [62, 95]; p = 1.9 × 10−12) of the association with maternal BMI and 94% (95% CI [72, 113]; p = 2.7 × 10−14) of the association with paternal BMI. Overall, this study found that the association between parental BMI and offspring BMI from age 6 months to 8 years may be primarily due to genetic confounding. These findings suggest that parental BMI do not have a large causal effect on childhood BMI. 

Click here to read this study in PLOS ONE

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