A fourth early belief was that 1 ppm fluoride in drinking water provided an ample margin of safety against toxic effects. Not only is there no safety margin for dental fluorosis but there is growing evidence that there may be no safety margin for changes to bone structure and impacts on the brain, thyroid, and other soft tissues, especially when it is coupled with nutrient deficiencies, particularly iodide. Two groups of rats were exposed to two different kinds of fluoride at 1 ppm in distilled water. A third group received only distilled water. The authors speculate that fluoride enables aluminum to cross the blood-brain barrier.
Skeletal fluorosis has several stages of severity, with the less severe being chronic joint pain.
Arthritis is now at epidemic levels in the U.S. Fluoride's plausible contribution has been ignored, but needs to be taken seriously. The dose of 1.58 to 6.6 mg per day overlaps the dose found to depress the functioning of the human thyroid gland. Recognizing that there are simple and effective alternatives, they have applied the precautionary principle. Their children's teeth have not suffered as a consequence. The American policy of giving fluoride to children by medicating whole communities with a potent drug that may harm some people seems a dubious practice at best.