This Is Why Some Boys And Girls Are Bigger Than Others

Young children play Auskick at the half time break at Patersons Stadium . Paul Kane/Getty Images

Is it in the genes or is it the influence of the environment?

Scientists have discovered that when it comes to size, or body mass, the genetic influences actually increase as children get older.

The influence of genetic factors on differences between children’s Body Mass Index increases from 43% at age 4 to 82% at age 10

A new study by researchers at UCL and King’s College London, published in the journal Obesity, analysed data from 2,556 pairs of twins.

The twins analysis confirmed previous studies with a doubling of genetic influence, called ‘heritability’, showing that the reasons that some boys and girls are bigger than others are 43% genetic at age 4 and 82% genetic at age 10.

One explanation for this may be that as children get older, they have increased independence to seek out environmental opportunities to express their genetic predispositions, a process ‘termed gene-environment correlation’.

“Our results demonstrate that genetic predisposition to obesity is increasingly expressed throughout childhood,” says Dr Clare Llewellyn, UCL Epidemiology and Public Health, who co-led the study.

“This underlines the importance of intervening at an early age to try to counteract these genetic effects and reduce childhood obesity.”

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