Background Occupational exposure to extremely low frequency magnetic fields (ELF-MF) is a suspected cancer risk factor, however, the epidemiological literature is limited and potential biological mechanisms unclear. Night shift work and associated circadian misalignment, leading to decreased melatonin production is also suspected in cancer. It has been suggested that ELF-MF exposure may decrease melatonin production leading to the promotion of cancer development, however previous findings are inconsistent. We assessed ELF-MF exposure and melatonin production in a recent study of male rotating shift workers.

Methods A total of 50 male shift workers rotating in a 3 week night, 3 week evening, and 3 week morning schedule were recruited at a local car manufacturing facility. Personal full-shift measurements of ELF-MF exposure were performed (EMDEX II, 40–800 Hz) and urine samples from all voids over 24 hour collected on two working days (end of 3 week night and end of 3 week morning shifts). Urinary concentrations of 6-sulfatoxymelatonin (aMT6s), the main melatonin metabolite, were measured in all samples (creatinine corrected), with the mesor (24 hour mean) derived based on cosinor models.

Results Arithmetic mean (AM (SD)) and geometric mean (GM (GSD)) ELF-MF levels were 0.05 (0.06) µT and 0.03 (0.02) µT, respectively. Peak production of aMT6s occurred 9 hours later in night compared with morning shifts, though with a similar mesor indicating adaptation. The adjusted mesor varied somewhat by age group and other personal characteristics, and was somewhat lower among those with higher AM and GM ELF-MF levels (i.e. ≥50 th or 75th percentile), with differences ranging from 0.94–1.38 ng/mg creatinine/hour in the morning to 0.96–4.33 in the night shift observed, with some differences significant.

Conclusions Overall, small differences in mean aMT6s levels were observed according to ELF-MF. Workers during the night shift adapted, showing a delay in the peak time of aMT6s production compared to the day shift.