Radiation doses from global fallout and cancer incidence among reindeer herders and Sami in Northern Finland

Objectives People in the Arctic regions are one of the most heavily exposed population from the global fallout from atmospheric atomic bomb testing of the 1950s and 1960s due to their diet rich in reindeer meat in which radionuclides accumulate. We estimated the effect of the radioactive fallout and ethnicity on the cancer incidence in Northern Finland. Methods A cohort of the Arctic population in Finland (n=34 653) was identified through the Population Register Centre with grouping by reindeer herding status, ethnicity and radiation exposure. Annual average radiation doses, based on Cs-137 whole-body measurements, were assigned by birth year, gender and reindeer herder status. Incident cancer cases of a priori selected cancer types in the study cohort during 1971-2005 were identified from the Finnish Cancer Registry. Results A total of 2630 cancer cases were observed versus 3073 expected on the basis of incidence rates in Northern Finland (standardised incidence ratio (SIR) was 0.86 with 95% CI of 0.82 to 0.89). For the indigenous Sami people SIR was even lower, 0.60 (95% CI 0.50 to 0.71). None of the cancer sites was significantly associated with the lifetime cumulative radiation dose. The SIR for the combined group of radiation-related cancer sites increased with the cumulative radiation dose received before 15 years of age (p=0.004). Conclusion Despite the low overall cancer incidence in the Arctic population and ethnic Sami people in Finland and lack of association between the lifetime cumulative radiation exposure from global radioactive fallout and cancer incidence, we found some indication of an increased cancer risk associated with radiation exposure received during childhood. Potential underestimation and misclassification of the radiation dose may affect the results and the findings should be interpreted with caution.