New research has established a small but statistically significant link between risk of childhood leukaemia and the gamma rays that humans are exposed to from their natural environment.

The study conducted by a team of Oxford University researchers along with colleagues from the US National Cancer Institute, The University of Manchester and the Health Protection Agency, has been published in the journal Leukemia.

According to the report, exposure to gamma rays from natural sources in the environment is not something that can readily be altered, but the study adds to our understanding of the small cancer risks associated with other low doses of radiation, such as from medical X-rays and CT scans. The findings demonstrate that there are small effects of radiation at very low doses.

Guidelines on exposure to low doses of radiation have largely been based on estimated risks from models using data from Japanese survivors of the atomic bombs, where radiation exposures were brief and very much higher. As a result, there have been some long-standing uncertainties about the extrapolation of these risks to low radiation doses.

The researchers concluded that the size of the increased risk of childhood leukaemia with natural gamma-ray exposure is consistent with these models and supports their continued use in radiation protection. The results of the study contradict the idea that there are no adverse radiation effects, or might even be beneficial effects, at these very low doses and dose rates.

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

It has needed a study of this very large size to be able to reliably identify the small effect of background radiation on childhood leukaemia. Previous studies have lacked the size and statistical power to be able to detect any link.

"We found a statistically significant correlation between natural gamma-rays and childhood leukaemia," stated lead researcher Dr Gerald Kendall of the Childhood Cancer Research Group at Oxford University. "What is new in our findings is the direct demonstration that there are radiation effects at these very low doses and dose-rates."

The researchers believe that the association between natural gamma-rays and childhood leukaemia is likely to be causal.