Back in the 1930s, scientists decided that adding fluoride to drinking water would protect teeth from decay. Bacteria in the mouth produces acid when sugary foods are eaten, and this acid, in turn, damages the surface of the teeth, weakening them and increasing the risk of cavities. These scientists believed that fluoride could help to rebuild and strengthen the teeth, and that providing “frequent and consistent contact with low levels of fluoride” via drinking water would, therefore, be a good idea.
Setting aside the fact that there is very little evidence to back up their theory, this “frequent and consistent contact” with fluoride has other, negative side effects for the human body. Fluoride is more toxic than lead and only slightly less toxic than arsenic. Overdosing on it could cause serious poisoning, and in big enough doses, even lead to death. It is not an acute overdose that natural healthcare practitioners are concerned about, however, but long-term, chronic exposure to fluoride. As noted by Green Med Info, this type of exposure can cause the pineal gland to calcify, hardens the arteries, and can increase risk of hypothyroidism, among other things.