Even low doses of gamma ray radiation in the natural environment can increase the risk of childhood leukaemia, according to an Oxford University study.

The results of the study contradict the idea that there are no adverse radiation effects with very small levels of gamma-rays.

The research adds to an understanding of the small cancer risks associated with other low doses of radiation, such as from medical X-rays or CT scans.

The study, based on tens of thousands of records from a UK national cancer registry, is the largest conducted on links between childhood cancers and natural background radiation levels.

Previous studies have been unable to detect any link.

Dr Gerald Kendall, of the Childhood Cancer Research Group at Oxford University, said: “What is new in our findings is the direct demonstration that there are radiation effects at these very low doses and dose-rates.

“In terms of preventing childhood cancers caused by natural gamma-rays, there’s not a lot you can do.

“We have estimated that about 15 per cent of the 500 or so cases of childhood leukaemia which occur annually in the UK are due to natural background radiation.

“Natural gamma-rays account for about half the dose reaching children’s bone marrow from all sources. So they account for approaching 40 childhood leukaemias a year.”

Gamma-rays in background radiation come largely from naturally occurring radioactive isotopes of uranium, thorium and potassium in the environment, reserachers said.