Hundreds of thousands of children in England are growing up overweight or obese because of widening health disparities across the country, analysis suggests.

Child obesity has proliferated in recent years for a variety of reasons. Children live increasingly sedentary lifestyles, where physical activity has fallen and activities such as watching TV, playing video games and spending time on phones have increased.

However, a new analysis suggests as many as one in 12 cases could be avoided if health outcomes in the worst parts of England were improved to match the best.

The analysis, performed by the Institute for Public Policy Research (IPPR) thinktank and the analytics consultancy LCP for the Guardian, suggests the number of overweight or obese children in England could be reduced by hundreds of thousands if health outcomes were levelled up to the areas of the country where they are best.

Of the 1.4 million 10- and 11-year-olds living in England, about 35% are overweight or obese, which is the equivalent of 488,586 children, the analysis shows. Their excess weight means they will face a higher risk of serious conditions, such as type 2 diabetes, heart disease or cancer later in life.

But if health outcomes everywhere improved to match the areas where they are traditionally best, such as the home counties and more affluent London boroughs, the proportion could be cut to 32%. That would mean 41,879 fewer overweight or obese children in year 6 this year alone.

Barking and Dagenham, the worst performing part of the country, has double the rate of overweight or obese children than the best area, Richmond upon Thames, according to the analysis. Barking and Dagenham also had nearly five times higher rates of child poverty and 10% lower levels of early years development compared with the best performing area. Both these variables had a statistically significant correlation to childhood obesity, the IPPR senior research fellow Chris Thomas said.

“Unless there is urgent intervention to tackle widening health disparities, our analysis suggests hundreds of thousands more children will grow up overweight or obese simply because of where they grew up,” Thomas said.

“Our figures suggests that thousands of cases of childhood obesity could be avoided, if the government take tough action on material inequalities and poverty. If not, obesity will pose a threat not only to people’s health – but to economic prosperity and levelling up.”

The new child obesity analysis follows an IPPR report which last week said multiple disadvantages were “conspiring” to drive down health outcomes and prevent life expectancy from growing across parts of England.

The thinktank is calling for the government to introduce an annual New Zealand-style public health budget, ringfencing 5% of total government spending for improving public health and closing health disparities. It said this would be worth approximately GBP35bn a year in England and could be put in motion at the comprehensive spending review this week.

“While the prime minister and his health secretary have recognised that stark health disparities exist in this country, they are currently failing to address the underlying causes,” said Thomas.

“Our analysis shows the material conditions of the places we live – and our exposure to poverty, wealth inequality, unemployment, poor education, worse early years development or lower access to local public health services – combine to undermine the health of many people in our country.

“This has a social cost, and an economic cost, and runs counter to the government’s ‘levelling up’ rhetoric.”