Children who live in homes with high radon levels may be at increased risk for acute lymphoblastic leukemia during childhood, research from Denmark suggests.

Children who live in homes with high radon levels may be at increased risk for acute lymphoblastic leukemia during childhood, but not other childhood cancers, research from Denmark suggests.

Acute lymphoblastic leukemia (ALL) is a cancer of infection-fighting white blood cells. Outside of fetal exposure to X-rays and genetic conditions, the causes or risk factors associated with childhood ALL are poorly understood.

Higher rates of childhood cancer, and particularly leukemia, have been observed in geographic regions with higher levels of radon - a natural radioactive gas that emanates from soils and can concentrate inside houses. Yet, studies assessing links between breathing radon gas and the risk for childhood cancer have yielded mixed results.

Against this backdrop, Dr. Ole Raaschou-Nielsen of the Institute for Cancer Epidemiology in Copenhagen, and colleagues looked at the lifetime radon exposures of 2,400 children who had been diagnosed with cancer between 1968 and 1994, and 6,697 cancer-free children.

All the children were born and living in Denmark, and were age 15 or younger. One-year radon measurements from regions in which the children lived were used to predict cumulative radon exposure.

The researchers found that children exposed to "intermediate" levels of radon had a 21 per cent higher risk of developing ALL relative to children exposed to the lowest levels of radon. Children with the highest radon exposures had a 63 per cent greater risk of ALL relative to those with the least exposure.

These associations held up in further analyses that factored in other characteristics potentially associated with increased cancer risk, such as mother's age, birth order, traffic density around the home, electromagnetic field exposures, and the building type of each home.

Raaschou-Nielsen and colleagues, who report their findings in the medical journal Epidemiology, say they have no obvious biological explanation for the suggested association between radon exposure and ALL.

In related commentary, Dr. Andrew F. Olshan, at the University of North Carolina in Chapel Hill, cautions that these findings may just be a signal to devise long-term, progressively refined studies that may or may not reveal definitive answers.

"The etiology of childhood cancer has remained elusive, especially with regard to possible environmental influences," Olshan noted.

Epidemiology, July 2008