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In the first of these studies, 18 men were exposed to 890 - 900 MHz from GSM telephones, with 217 Hz frequency modulation at 576 microsecs pulse width, for 2 hours per day, 5 days per week, for 4 weeks. Exposure to other EMFs was restricted during this time. Blood hormone levels (ACTH, TSH, LH, GH, FSH) remained within the normal range throughout the study. However, TSH (thyroid stimulating hormone) average levels decreased 21% by the seventh sample, which was the last in the exposure period. The levels increased to baseline levels in the post-exposure period. There was no obvious explanation for this fluctuation. The authors state that they plan to repeat the study, with a greater number of volunteer subjects. In the second study, 37 men were exposed to either a GSM 900 or DCS 1800 device, frequency modulated as in the first study, and for identical time periods. On this occasion blood melatonin levels were studied before, during, and after exposure. Melatonin levels usually increase during the night. No disturbance in the normal pattern was seen, and the levels of the hormone remained normal throughout the study.
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