Magnetic fields from indoor transformer stations and risk of cancer in adults: a cohort study.

Objectives: Studies assessing the association of adult cancers with extremely low frequency (ELF) magnetic fields (MF) have provided inconclusive results, probably affected by limitations such as low exposure levels, confounding and various forms of bias. This study investigated the association between residential ELF MF exposure and adult cancer using a design that avoids the main limitations of previous studies.

Methods: Persons who have lived in buildings with indoor transformer stations during the period 1971-2016 formed the study cohort. Their MF exposure was assessed based on the location of their apartment in relation to the transformer room. Information on their cancer diagnoses was obtained from the Finnish Cancer Registry. SIR with 95% CI was calculated to investigate the association of MF exposure with overall cancer and specific cancers.

Results: The SIR for all primary sites was 1.01 (95% CI 0.93 to 1.09). An increased risk of digestive organ cancers was observed among the exposed persons, with a SIR of 1.23 (95% CI 1.03 to 1.46). The highest SIR was observed for gallbladder cancer (3.92, 95% CI 1.44 to 8.69). Increased risk of testicular cancer was observed among men exposed to MF during childhood, but this is likely to be due to confounding associated with living on the lowest floors. No other significant associations were observed for other primary cancer sites studied.

Conclusions: Overall cancer risk was not affected by residential MF exposure. The increased risk of digestive organ cancers among MF-exposed persons is a novel finding requiring confirmation in further studies.