title: Experiments on effects of an intermittent 16.7-Hz magnetic field on salivary melatonin concentrations, rectal temperature, and heart rate in humans.
abstract: OBJECTIVE
  The present experiments concerned the hypothesis that an intermittent, strong and extremely low frequency magnetic field reduces salivary melatonin levels and delays consecutively the nadirs of rectal temperature and heart rate.
  
  
  METHODS
  Twelve healthy young men (18-25 years) participated in three randomly permuted sessions, which were performed as constant routines. The participants kept a strict bed rest over 26 h, air temperature was 20 degrees C, illumination < 30 lx, and sound level < 50 dBA. Salivary melatonin levels were determined hourly, rectal temperature and heart rate were registered continuously throughout. An intermittent magnetic field was administered in one session from 6 p.m. to 2 a.m. at 16.7 Hz, 0.2 mT and alternating on/off-periods of 15 s. This situation was compared with a control session without any additional stress. Another session was performed to determine the participants' ability to respond to a well-known melatonin-suppressing stress, namely bright light (1,500 lx, 10 p.m.-2 a.m.).
  
  
  RESULTS
  Bright light inhibited melatonin synthesis in all 12 participants and delayed the nadirs of rectal temperature and heart rate. The only significant alteration that was associated with exposure to the magnetic field was a delay in the heart rate nadir, which was not mediated by an accordingly altered melatonin profile.
  
  
  CONCLUSIONS
  The fact that the circadian rhythm of only the heart rate was altered indicates an internal dissociation which might constitute a health risk in the long run and needs to be investigated more extensively.
authors.affiliation: Institute for Occupational Physiology, University of Dortmund, Germany. griefahn@arb-phys.uni-dortmund.de
authors.forename: Barbara
authors.initials: B
authors.lastname: Griefahn
authors.forename: Christa
authors.initials: C
authors.lastname: Künemund
authors.forename: Meinolf
authors.initials: M
authors.lastname: Blaszkewicz
authors.forename: Klaus
authors.initials: K
authors.lastname: Golka
authors.forename: Gisela
authors.initials: G
authors.lastname: Degen
mesh_terms: D000328:Adult; D001831:Body Temperature; D002940:Circadian Rhythm; D003625:Data Collection; D004781:Environmental Exposure / Q000009:adverse effects; D006339:Heart Rate; D006801:Humans; D008027:Light / Q000009:adverse effects; D008280:Magnetics / Q000009:adverse effects*; D008297:Male; D008550:Melatonin / Q000032:analysis / Q000096:biosynthesis*; D016273:Occupational Exposure / Q000009:adverse effects; D012007:Rectum; D012463:Saliva / Q000737:chemistry*
chemical_list: D008550:Melatonin