A very interesting study conducted on 900 Mhz frequencies found that they reduced thyroid function in rats. 30 minutes per day, 5 days per week for 4 weeks only. Compare this to the average person talking on the cell phone for hours a day seven days per week, 52 weeks per year for many years. By the way, regular cordless phones are also frequently at 900Mhz, so these can also cause problems. Now other frequencies are being used as well, but we don’t yet have data on how they may be affecting us. Note that the study said it “lowers TSH and T4 and T3″, but they probably meant that it raises TSH and lowers T4, T3. Regardless, T3 is the more active form so if that is reduced then your thyroid function is reduced.
 
Toxicol Lett. 2005 Jul 4;157(3):257-62.