The sensory cells of the inner ear are vulnerable to several agents (aminoglycosides, cytostatics, ionizing irradiation). The effect of strong magnetic fields occurring in industries with production based on electrolytic processes and with medical magnetic resonance equipment is unknown. The aim of this study was to clarify the effect of strong static magnetic fields on the inner ear, by exposing 11 healthy men to a magnetic field with flux density of 2-7 mT for 9 h. No damage was found to the acoustic or vestibular system.

The present study sought to evaluate possible acute effects on 6-sulfatoxymelatonin (aMT6s) excretion, a surrogate for melatonin levels in blood, in volunteers exposed to static magnetic fields with flux densities representative for workers in light metal reduction plants and operators of medical MRI in hospitals. Eleven healthy male volunteers (23-43 years) participated. Urine samples were collected for two consecutive 24 h periods from 22:00 hours day 1 (exposure day) through day 2 (day after exposure) and then for 24 h from 07:00 hours on day 7 (control day). On the day of exposure the subjects slept in the MRI room from 22:00 hours until 07:00 hours next morning, thus receiving a 9 h exposure to the magnetic field (2-7 mT). On the day after exposure and on the control day, they slept at home and otherwise performed their ordinary daily activities. Total daily urine production was collected in four parts: 22:00-07:00 hours, 07:00-11:00 hours, 11:00-18:00 hours, 18:00-22:00 hours, and the volume for each interval was measured and recorded. Samples were transferred to coded bottles and frozen for later RIA analysis of aMT6s. Pairs of values of mean hourly aMT6s excretion, both diurnal and for the four daily intervals, were compared using two-sided Wilcoxon signed ranks test. The day of exposure and the day after exposure were not significantly different from the control day, either for the total diurnal secretion or the interval data. In summary, the study shows no association between a single nocturnal exposure to a static magnetic field of strength 2-7 mT and excretion of aMT6s in urine.

<strong><span style="font-family: TimesNewRomanPS-BoldMT;"><span style="font-family: TimesNewRomanPS-BoldMT;"><p align="left"> </p></span></span><span style="font-size: x-small; font-family: TimesNewRomanPS-BoldMT;"><span style="font-size: x-small; font-family: TimesNewRomanPS-BoldMT;">SAMMENDRAG</span></span></strong><span style="font-size: x-small; font-family: TimesNewRomanPSMT;"><span style="font-size: x-small; font-family: TimesNewRomanPSMT;"><p align="left">I denne studien har vi undersøkt om det finnes noen sammenheng mellom målte verdier av urinmetabolitten</p><p align="left">6-sulfatoxymelatonin (aMT6s) tatt ut i porsjoner gjennom døgnet og selvrapportert døgnrytme hos en</p><p align="left">gruppe norske skiftarbeidere. Studien omfatter 19 arbeidstakere ved to produksjonsenheter ved Hydro</p><p align="left">Porsgrunn, magnesiumfabrikken og fullgjødselfabrikk 3. Etter å ha deltatt i en studie der urinprøver ble</p><p align="left">samlet inn, svarte de involverte senere på et spørreskjema om søvn og døgnrytme. Resultatene indikerer at</p><p align="left">egenrapporterte B-type mennesker har en tendens til høyere midlere timeutskillelse av aMT6s analysert på</p><p align="left">døgnbasis første døgn med nattskift, og en signifikant høyere nattutskillelse (8 timer) i et kontrolldøgn</p><p align="left">hjemme. I fremtidige studier av melatoninsekresjon og utskillelse av metabolitt i urin, kan det være av</p><p align="left">interesse samtidig å samle inn spørreskjemabaserte opplysninger om døgnrytmetype og utfyllende opplysninger</p><p align="left">om søvn og søvnmønster i relasjon til eksponeringer som skiftarbeid og andre arbeidsmiljøfaktorer</p><p align="left">som kan ha effekt på hormonbalansen.</p><span style="font-size: x-small; font-family: TimesNewRomanPSMT;"><span style="font-size: x-small; font-family: TimesNewRomanPSMT;"><p align="left">Tynes T, Haugsdal B, Tønnessen A, Kleiven M.</p></span></span></span><span style="font-size: x-small; font-family: TimesNewRomanPSMT;"><p align="left"> </p></span></span><p align="left"><strong><span style="font-size: x-small; font-family: TimesNewRomanPS-BoldMT;"><span style="font-size: x-small; font-family: TimesNewRomanPS-BoldMT;">Individual variations in excretion of<p align="left">6-sulfatoxymelatonin in morning and evening type Norwegian shift workers.</p></span></span></strong><em><span style="font-size: x-small; font-family: TimesNewRomanPS-ItalicMT;"><span style="font-size: x-small; font-family: TimesNewRomanPS-ItalicMT;"><em><span style="font-size: x-small; font-family: TimesNewRomanPS-ItalicMT;"><span style="font-size: x-small; font-family: TimesNewRomanPS-ItalicMT;"><p align="left">Nor J Epidemiol</p></span></span></em></span><em><span style="font-size: x-small; font-family: TimesNewRomanPS-ItalicMT;"><p align="left"> </p></span></em></span><strong><span style="font-size: x-small; font-family: TimesNewRomanPS-BoldMT;"><span style="font-size: x-small; font-family: TimesNewRomanPS-BoldMT;">ENGLISH SUMMARY</span></span></strong><span style="font-size: x-small; font-family: TimesNewRomanPSMT;"><span style="font-size: x-small; font-family: TimesNewRomanPSMT;"><p align="left">The aim of this study was to evaluate whether there is an association between measured values of the urine</p><p align="left">metabolite 6-sulfatoxymelatonin (aMT6s) in samples collected at selected intervals and self-reported diurnal</p><p align="left">rhythm in a group of Norwegian shift workers. The study included 19 workers at two production units</p><p align="left">at Hydro Porsgrunn, the magnesium factory and fertiliser factory 3. After submitting the urine samples</p><p align="left">used for the study, subjects filled in a questionnaire on sleep and diurnal rhythm at a later date. The results</p><p align="left">indicate that self-reported evening type subjects have a tendency towards a higher mean hourly aMT6ssecretion</p><p align="left">first day on night shift, and a significantly higher night secretion (8 hours) analysed for a control</p><p align="left">day at home. In future studies on secretion of melatonin and its metabolite in urine, the collection of</p><p align="left">questionnaire-based information on diurnal type, sleep and sleep pattern in relation to exposures like shift</p><p>work, and other work-related factors with potential effect on hormone balance might be of interest.</p></span></span></em><span style="font-size: x-small; font-family: TimesNewRomanPSMT;"><span style="font-size: x-small; font-family: TimesNewRomanPSMT;">1999; </span></span><strong><span style="font-size: x-small; font-family: TimesNewRomanPS-BoldMT;"><span style="font-size: x-small; font-family: TimesNewRomanPS-BoldMT;">9 </span></span></strong><span style="font-size: x-small; font-family: TimesNewRomanPSMT;"><span style="font-size: x-small; font-family: TimesNewRomanPSMT;">(1): 33-38.</span></span></p>