Background Exposure to domestic radon is hypothesized to cause childhood leukaemia but evidence from previous research has produced inconsistent results. Aims To investigate the association between domestic radon exposure and childhood leukaemia Methods A nationwide census-based cohort study including all children aged between 0 and 15 years and living in Switzerland on 5 December 5th 2000 was conducted. The follow-up period lasted until the date of diagnosis, death, emigration, the children becoming 16 years old or 31 December, 2008. Cox proportional hazard regression models were applied, adjusted for age, gender, birth order, socio-economic status of the parents, environmental gamma radiation and period effects. Exposure assessment for each individual home address was based on a radon prediction model, developed and validated with approximately 45,000 measurements carried out all over Switzerland. Results In total, 285 childhood leukaemia cancer cases were included in the study. Compared to the group of children exposed to a radon concentration below the median (＜ 77.7 Bq/m~3), the hazard ratio for the 10% highest exposed children (≥ 139.9 Bq/m~3) was 0.99 (95% CI: 0.66,1.49). The hazard ratios fort the intermediate exposure group (77.7-139.9 Bq/m~3) was 0.87 (95%-CI: 0.67,1.12). A separate analysis for acute lymphoblastic leukaemia (ALL), the most frequent subgroup of all leukaemias did not indicate significant associations either. Conclusions This census-based cohort study does not indicate an association between domestic radon concentration and childhood leukaemia. The observed lack of an association between domestic radon exposure and childhood leukaemia was found to be in line with estimated doses of domestic radon concentrations to red bone marrow.
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