The risk of multiple myeloma associated with daily low-dose exposure to ionising radiation from radon decay

Background Ionising radiation is suspected to increase the risk of multiple myeloma (MM) but has mostly been investigated at occasional high doses rather than exposure to continuous low doses at home. Methods In this ecological study, we investigated the association between MM and radon based on the geographical distribution of MM patients in Denmark diagnosed from 2005 to 2020 and a national radon survey carried out by the Danish authorities based on 3019 random selected single-family houses. A linear association was assessed between age- and sex-standardised incidence rate (SIR) of MM and radon concentration of each municipality. Municipalities were categorised into four classes based on the estimated fraction of dwellings exceeding 200 Bq/m 3 in each municipality, where SIR of class 1 (lowest radon exposure group) was compared to the SIRs of class 2–4 by incidence rate ratios (IRRs). Results Based on 5218 included patients distributed among 275 municipalities, no statistically significant association was found. The IRRs revealed a small inverse association due to 17 % lower SIR in class 4 as compared to class 1. Conclusions The lack of a positive association suggests no increased risk of MM in areas with higher radon concentrations in homes based on aggregated data. These findings must be clarified in individual-level based studies.