Experts found the biggest risks for children who were a normal weight when they were seven, but who became overweight by age 13.

Researchers already know that around a third of kidney cancer cases are preventable, with obesity linked to 24 per cent of cases.

For the study, led by experts from the Danish Centre for Clinical Research and Prevention at Bispebjerg and Frederiksberg Hospital, data from 301,422 people - half of whom were men - was examined.

All were born from 1930 to 1985 and had their weight and height recorded at annual school health examinations between the ages of seven and 13.

Cases of kidney cancer were then identified from the Danish Cancer Registry and the risk of the disease was calculated.

During an average follow-up of 32 years, 1,010 individuals were diagnosed with kidney cancer.

The experts found that in a pair of 13-year-old boys of similar height, where one was 5.9kg heavier, the heaviest boy had a 14 per cent increased risk of kidney cancer compared to the lighter child.

The same was true for a pair of 13-year-old girls where the heaviest girl was 6.8kg heavier.

When it came to height, a 13-year-old boy who was 8cm taller than his peer had a 12 per cent increased risk of kidney cancer in later life.

The same was true for a pair of girls where the taller one was 6.9cm taller.

Compared to children of normal weight at age seven and 13, children who were overweight at both ages did not have increased risks of kidney cancer.

But children who were a normal weight aged seven and overweight at age 13 had a 67 per cent greater risk of developing the disease.

The study was presented at the European Congress on Obesity in Glasgow and has been peer-reviewed by conference officials.

Lead author Dr Britt Wang Jensen said: "We know that overweight in adulthood is associated with an increased risk of RCC (renal cell carcinoma).

"We also know that cancers take many years to develop. We therefore had a theory that already being overweight in childhood would increase the risk of RCC later in life.

"We have found in other studies that childhood height is positively associated with several cancer forms.

"Therefore, we did expect to find that tall children have a higher risk of RCC than average-sized children."

Australian Associated Press