Fluorine itself is a poisonous gas, as are the related elements chlorine and bromine. Fluorine, as fluoride, is found in the earth's crust in combination with other minerals, and is also part of seawater. Fluoride is available naturally in the diet as calcium and sodium fluoride. It is sodium fluoride that is added to the drinking water of many cities to help reduce dental caries. There is some controversy as to whether fluoridation has some subtle poisoning effect or whether it is nontoxic and beneficial. In my opinion, fluoridated water is another example of technology's treating the effect instead of correcting the cause, which is primarily poor diet.

Fluoride is probably not essential to humans, though it is helpful in strengthening the bones and teeth. It is found only in trace amounts, about 2-3 grams, in the body, and most of that is in bones and teeth. The blood level of fluoride is about 0.3 mg. per 100 ml. Fluoride has no known function other than strengthening teeth and bones.

Intestinal absorption of fluoride, especially the more soluble sodium fluoride, is fairly good. Calcium, aluminum, and perhaps other minerals may interfere somewhat with absorption by making less soluble fluoride salts. About half of ingested fluoride, about 3 mg. per day, is eliminated through the kidneys and a little more through perspiration. The remainder is stored mainly in the bones.

Sources: Natural fluoride is present in the ocean as sodium fluoride, so most seafood contains some. People who eat large quantities of fish, such as the cultures of the Caribbean, have been shown to have stronger teeth and less incidence of dental cavities, the most common disease worldwide, than do others. This may also be related to other factors. Gelatin and tea also contain fluoride. In fact, a study showed that school children in England were obtaining over 1 mg. of fluoride daily from tea alone (that is black tea, with caffeinelike molecules theophylline or theobromine plus tannic acid, not herbal teas). Most plant-source foods contain some fluoride, though the amount can vary greatly depending on soil fluoride content. Soil deficiency of fluoride is fairly common.

Fluoride is added to the drinking water of many municipalities at the concentration of 1 ppm. More than 2 ppm can cause problems, so the concentration must be finely monitored. People drinking city water who also consume fluoride-containing foods or black teas can develop fluoride problems as well, though toxicity has not been found to be appreciable with moderate amounts.

Stannous (tin) fluoride was originally used in toothpaste for protection against tooth decay. But it has been found that fluoride is more effective in this area when provided internally by drinking water than when it is applied locally, and we probably do not want too much extra tin anyway (though tin may be an essential mineral in trace amounts as well). Overall, I do not advocate drinking fluoridated water-or any city water, for that matter (see Chapter 1, Water). It is better, I believe, to drink filtered water to be safe from chemical and toxic metal pollutants and to eat a more natural diet with some seafood, which is also thought to protect against atherosclerosis and heart disease as well as keep the teeth healthy.