Residential radon exposure and leukemia: A meta-analysis and dose-response meta-analyses for ecological, case-control, and cohort studies

Introduction: In this study, the authors conducted a comprehensive systematic review and meta-analysis (including a dose-response meta-analysis) for a possible causal association between residential radon exposure and leukemia. All 3 types of study design, including ecological, case-control, and cohort studies, were included in this study. In particular, different measurement units of radon exposure among studies were dealt with and analyzed thoroughly. Methods: A medical librarian searched MEDLINE (PubMed), EMBASE, and the Cochrane Library (from January 01, 1970 to November 05, 2020). For ecological studies, a conventional meta-analysis and subgroup analyses with meta-ANOVA analyses were conducted. For case-control and cohort studies, a two-stage dose-response meta-analysis was conducted. Results: A total of 8 ecological, 9 case-control, and 15 ecological-cohort studies were analyzed. For ecological studies, the pooled correlation coefficient was 0.48 (95% CI 0.41-0.54). In the meta-analysis of variance (ANOVA) analyses, the age group (childhood vs. adult) showed a statistically significant result (Q = 7.93 andp = 0.019) with the pooled correlation coefficient for childhood, adult, and all age group of 0.67 (95% CI 0.53-0.77), 0.46 (95% CI 0.05-0.74), and 0.44 (95% CI 0.36-0.51), respectively. For case-control studies, the dose-response meta-analysis showed the pooled OR increase of 1.0308 (95% CI 1.0050-1.0573) for each 100 Bq/m(3) increase of radon dose. The pooled OR increase was 1.0361 (95% CI 1.0014-1.0720) for each 100 Bq/m(3) increase of radon dose for lymphoid leukemia subgroup and 1.0309 (95% CI 1.0050-1.0575) for each 100 Bq/m(3) increase of radon dose for childhood leukemia subgroup. Because of the inclusion of ecological studies with larger exposure assessment units, the pooled RR from ecological-cohort studies should be interpreted conservatively (a tendency towards a higher risk estimate). The overall pooled RR increase for each 100 Bq/m(3) increase of radon dose was 1.1221 (95% CI 1.0184-1.2363). The pooled RR increase was 1.2257 (95% CI 1.0034-1.4972) for each 100 Bq/ m(3) increase of radon dose for the myeloid leukemia subgroup and 1.2503 (95% CI 1.0233-1.5276) for each 100 Bq/m(3) increase of radon dose for adult leukemia subgroup. Discussion: A number of epidemiologic concepts, including the issue of sample size justification, the possibility of differential participation selection bias for case-control studies, the possibility of random and systematic errors in radon measurement, ecological fallacy for ecological studies, were discussed. The effect of age group, socio-economic status, and gamma radiation exposure was also discussed. Future more accurate and conclusive large-scale case-control and cohort studies are needed.

Automated summary

This study conducted a comprehensive review and meta-analysis on the possible causal association between residential radon exposure and leukemia. Various types of studies were included, showing a correlation between radon exposure and leukemia, with different responses among age groups and leukemia types. Further large-scale studies are needed for more accurate conclusions.