Study ties parent-child BMI link mainly to genetics

A new study reports that the link between parents’ body mass index and their children’s BMI through age 8 appears to be driven largely by inherited genes. The finding could affect how public health officials think about programs that try to reduce childhood obesity by focusing on parents’ weight before pregnancy.

The analysis, published in PLOS Medicine, was led by Tom Bond of the University of Bristol with colleagues from the University of Queensland and other institutions. The researchers examined data from the Norwegian Mother, Father and Child Cohort Study, a prospective birth cohort of children born from 1999 to 2009.

Large family dataset

The study used records for 86,000 children, according to the researchers. The dataset included birth weight, BMI measurements from 6 months to 8 years of age, and appetite-related eating behaviors recorded at age 8.

To separate genetic inheritance from other family effects, the research team analyzed relationships among twins, siblings and half-siblings across multiple generations. The authors said that design allowed them to estimate how much of the parent-child BMI association was due to shared genes rather than direct biological effects of parental weight during pregnancy.

Higher parental BMI has long been associated with higher BMI in children, according to the PLOS Medicine paper. The challenge, the authors said, has been determining whether the association reflects genetics, the environment in the womb, parenting behavior or other shared family factors.

Birth weight showed a different pattern

The researchers found that a mother’s BMI was more strongly linked with a child’s birth weight than a father’s BMI. The authors said that pattern is consistent with an effect of maternal body weight through the intrauterine environment.

After birth, however, maternal and paternal BMI showed broadly similar associations with children’s BMI between ages 2 and 8, according to the study. The researchers estimated that genetic effects accounted for 79% of the statistical association between maternal BMI and child BMI at age 8, and 94% of the association between paternal BMI and child BMI at that age.

The study also linked higher parental BMI with obesity-related eating behaviors in children, including greater food responsiveness and emotional overeating. The authors said they could not determine conclusively how much of those behavioral associations was explained by genetics.

Limits for prevention efforts

The authors said the results do not mean children of heavier parents are destined to have higher BMI. They said children who inherit genetic risk may express those genes differently depending on their environment.

The researchers also said the findings do not reduce the importance of maternal health during pregnancy. They noted that maternal obesity is already established as a risk factor for adverse perinatal outcomes for both mother and child.

In the paper, the authors wrote that reducing either parent’s BMI before pregnancy may be unlikely to produce large reductions in childhood adiposity. Bond said the findings suggest the BMI link between parents and children up to age 8 is mainly explained by inherited genes, while expectant parents should still be encouraged to maintain a healthy weight.

David Evans, one of the researchers, said maternal BMI during pregnancy appeared likely to affect birth weight, but did not appear to have large later effects on offspring obesity risk beyond genetic transmission. Alexandra Havdahl said the findings point to shared genes rather than the intrauterine environment or parenting behavior as the main driver of the parent-child BMI association.

The paper is titled “Parental body mass index and offspring childhood body size and eating behaviour: A structural equation modelling analysis in the Norwegian Mother, Father and Child Cohort Study.” Its DOI is 10.1371/journal.pmed.1005094.

This story draws on original reporting from Medical Xpress.