Heavier and taller children may be at an increased risk of developing kidney cancer as adults, a study has found.

Renal cell carcinoma (RCC) is the most common form of kidney cancer found in adults. Although it often occurs in men between the ages of 50 and 70, the cancer can be diagnosed throughout adulthood.

Medical experts do not know the exact causes of RCC.

"We know that overweight in adulthood is associated with an increased risk of RCC. We also know that cancers take many years to develop," said Britt Wang Jensen, from the Bispebjerg and Frederiksberg Hospital in Denmark.

"We therefore had a theory that already being overweight in childhood would increase the risk of RCC later in life," Jensen said in a statement.

To tease out the relationships between childhood body size and the risk of RCC in adulthood, researchers used data from 301,422 children born in Copenhagen in the years 1930 to 1985.

The weights and heights were measured at annual school health examinations at the ages 7-13 years.

During about 32 years of observation, 1,010 individuals (680 men) were diagnosed with RCC. Among men and women significant and positive associations were observed between childhood BMI and height, respectively, and RCC risk.

When comparing two 13-year old children with one z-score difference in BMI -- equivalent to 5.9 kg for boys and 6.8 kg for girls -- but with similar height, the heaviest child had a 14 per cent higher risk of RCC than the leaner child.

For height, a one z-score difference in two 13-year old children was associated with a 12 per cent increased risk of RCC later in life for the taller boy or girl.

"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," researchers said.

"Our findings that heavier and taller children have increased risks of RCC opens the door to new ways to explore the causes of kidney cancer," they said.