According to a new study published in PLOS Medicine by Tom Bond from the University of Bristol in the UK and his colleagues at the University of Queensland in Australia and other institutions, the link between parents’ body mass index (BMI) and their children’s BMI during childhood may be primarily driven by genetic predisposition rather than any direct biological effect of parental weight during pregnancy.
A higher parental BMI is consistently associated with a higher childhood BMI. Researchers find it challenging to determine how much of this association stems from genetic factors versus biological effects of maternal weight during pregnancy. This distinction could influence interventions aimed at managing childhood BMI by targeting parental weight before conception.
In this new study, scientists analyzed data from the Norwegian Mother, Father and Child Cohort Study, a prospective cohort study of children born between 1999 and 2009.
The dataset included information on 86,000 children, covering their birth weight and BMI from 6 months to 8 years of age, as well as appetite-related eating behaviors at age 8. Researchers examined family relationships among twins, siblings, and half-siblings across multiple generations to directly quantify how much of the parent-child BMI correlation could be attributed to genetic factors.
Maternal BMI was more strongly linked to newborn weight than paternal BMI, consistent with the influence of maternal weight on birth weight through the intrauterine environment.
However, after birth, the associations between both maternal and paternal BMI and offspring BMI remained broadly similar from ages 2 to 8. Models indicated that genetic effects accounted for approximately 79% of the statistical link between maternal BMI and child BMI at age 8, and 94% of the link for fathers.
Higher parental BMI was also associated with obesity-promoting eating behaviors in children, such as increased food responsiveness and emotional overeating, though the study could not definitively determine how much of this was genetically driven.
The authors caution that these findings do not support the idea that childhood obesity is inevitable for children whose parents are overweight. Children who inherit a genetic predisposition to a higher BMI may express these genes differently depending on their environment.
The results also do not undermine the importance of maternal health during pregnancy, the authors note. It is well established that maternal obesity raises the risk of adverse perinatal outcomes for both mother and child.
“Our findings could have significant public health implications when considered alongside previous evidence,” they write. “Maternal BMI is unlikely to have a substantial causal effect on child BMI after birth… and any causal effect of paternal BMI on offspring BMI in childhood is likely to be similar to or smaller than that of maternal BMI. Consequently, reducing the BMI of either parent before pregnancy is unlikely to lead to a major reduction in childhood obesity.”
“Obesity runs in families, but it’s difficult to understand why. Our results suggest that the link between the BMI of mothers or fathers and their children’s BMI up to age 8 is largely due to inherited genes. Future parents should be advised to maintain a healthy weight, but this may not be enough to ensure a healthy weight in their children,” says Bond.
“We were interested in whether maternal obesity during pregnancy might also have adverse effects on the obesity risk of their offspring as children grow older,” notes David Evans. “We found that, while maternal BMI during pregnancy likely negatively impacts newborn weight, it does not appear to have a substantial effect on later obesity risk in offspring beyond what is explained by the transmission of genes from mothers to their children.”
“Our results indicate that the association between parental and child BMI is largely due to shared genes, rather than the intrauterine environment or parenting practices,” adds Alexandra Havdahl.
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