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The influence of genetic factors on differences between children's Body Mass Index (BMI) changes from 43 percent at age 4 to 82 percent at age 10, according to a new study. 

The research combined twin and genomic analyses in more than 2,500 pairs of twins from the Twins Early Development Study. Researchers collected the data in England and Wales between 1999 and 2005 when the twins were 4 and 10 years old respectively. 

The analysis confirmed the previous studies with doubling the genetic influence dubbed 'heritability'. Researchers said it might be that as children get older, they increase their independence to seek out environmental opportunities to express their genetic predispositions. 

Researchers had to use the genomic data in the same sample to compare with the twin findings as the previous twin analyses didn't involve direct measurement of the genes. 

"Our results demonstrate that genetic predisposition to obesity is increasingly expressed throughout childhood," said Dr Clare Llewellyn, UCL Epidemiology & Public Health, who co-led the study, in the press release. "This underlines the importance of intervening at an early age to try to counteract these genetic effects and reduce childhood obesity."

"The fact that the twin-based estimates of increasing heritability of BMI were supported by genomic data provides strong support for the reliability of twin analyses," added Dr Maciej Trzaskowski of the MRC Social, Genetic and Developmental Psychiatry Centre at King's College London in the press release, who also co-led the study. 

"Given the time and expense incurred collecting DNA in large studies, twins offer a convenient and affordable alternative to describing the genetic architecture of a range of health-related characteristics such as body weight."

The research has been published in the journal Obesity.