A new study analysing data from about 86,000 Norwegian children found that genetic factors accounted for an estimated 79 per cent of the statistical association between a mother's body mass index (BMI) and her child's BMI at age eight, and 94 per cent of the association for fathers.

Higher parental BMI was also linked to obesity-related eating behaviours in children, including greater responsiveness to food and emotional overeating. However, the study, published in the journal PLOS Medicine, could not conclusively determine the extent to which this association was genetically driven.

Researchers from the Norwegian Institute of Public Health and universities of Bristol in the UK and Queensland in Australia analysed data from the 'Norwegian Mother, Father and Child Cohort Study', a prospective birth cohort of children born between 1999 and 2009.

Birth weight and BMI of the children from age six months to eight years, along with appetite and eating behaviours at age eight, were analysed.

The researchers looked at twin, sibling, and half-sibling relationships across multiple generations to directly quantify how much of the parent-child BMI association could be attributed to genetic confounding.

"For 8-year BMI, genetic confounding explained 79 per cent of the covariance (joint variability) with maternal BMI and 94 per cent of the covariance with paternal BMI," the authors wrote.

Maternal BMI was more strongly associated with offspring birth weight than paternal BMI, consistent with an effect of maternal body weight on birth weight through the environment inside the uterus.

However, after birth, the associations between maternal and paternal BMI and the child's BMI were found to be broadly similar from ages two to eight.

The association between parents' BMI and their children's BMI during childhood may be primarily due to genetic inheritance rather than any direct biological effect of parental weight during pregnancy, the researchers said.

The team added that while a higher parental BMI has been consistently associated with a higher childhood BMI, it has been difficult for scientists to separate the role of genetics and that of biological effects of maternal weight during pregnancy.

The study may have implications for interventions that aim to control childhood BMI by targeting pre-conception parental weight, they said.

The authors caution that the findings do not support the idea that childhood obesity is inevitable for children of heavier parents.

Children inheriting a genetic predisposition to a higher BMI may still express the genes differently depending on the environment, they said.

The results also do not argue against the importance of maternal health in pregnancy, as maternal obesity is well established to increase risk of adverse perinatal outcomes for both mother and child, the team said. KRS MG MG

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