EFFECTS OF EXPOSURE TO 16.7 HZ MAGNETIC-FIELDS ON URINARY 6-HYDROXYMELATONIN SULFATE EXCRETION OF SWISS RAILWAY WORKERS

The aim of our study was to examine the effects of 16.7 Hz electromagn etic-field exposure on pineal melatonin production in healthy humans. The study was based on comparing urinary 6-hydroxymelatonin sulfate (6 -OHMS) levels of 108 male railway workers between leisure periods and days following the start of service on electrically powered engines (6 6 engineers) or working beneath transmission lines (42 railway employe es such as train attendants and station managers; controls). A repeate d measures design was used, i.e., each volunteer served as his own con trol. The exposure averaged 20 mu Tesla in the most exposed workers an d around 1 mu Tesla in the least exposed. Apart from magnetic exposure the workers were subject to a shift work schedule with daily advances between 15 min and 1 hr. Melatonin was assessed by sampling urinary 6 -OHMS both in the morning and the early evening. Evening 6-OHMS values appeared to be lowered by a factor of 0.81 (95%Cl: 0.73-0.90) during work days compared to leisure days among engine drivers, but not in th e controls. The lowering was not confined to certain types of shift wo rk such as early, normal, or late shifts. During subsequent leisure pe riods evening values recovered significantly, mean ratio=1.27 (95%Cl: 1.03-1.56), i.e., the effects appeared to be reversible. In contrast, morning 6-OHMS samples of engineers and controls did not differ much b etween work and leisure days. There was, however, a tendency for a reb ound of morning values in a leisure period following a work period bot h for engineers and controls. The observed pattern appears to be in li ne with predictions of the ''phase response curve.'' No evidence for a dose-response relation was found. The results support the hypothesis that 16.7 Hz magnetic fields alter 6-OHMS excretion in humans exposed to magnetic fields. An alternative explanation that cannot be excluded in this study is that the difference between engineers and controls i s due to differential exposure to day light at work.