Fluoride in The Body – What it does

ftoxicFluoridation Free Ottawa
Mar 2, 2014


WHAT HAPPENS to fluoride once it has entered the human body? To answer this question one of two methods is usually used.

In one the total quantity of fluoride consumed over a given period from all food and drink is measured and compared with the amounts of fluoride eliminated through the kidneys and bowels. This approach, however, is only partially reliable because some fluoride leaves the body with sweat, saliva, and tears, all of which are difficult to collect. The procedure was first reported in 1891 by two German pharmacologists, J. Brandl and H. Tappeiner, who over the course of 21 months fed slightly more than 14 ounces (403 g) of sodium fluoride to a 28-pound dog.1 During this period the dog excreted 81 % of the fluoride through the kidneys and bowels. Of the fluoride detected in the dog when they then killed it, over 92% was present in the bones and cartilage. The rest, in decreasing amounts, was found in the skin, muscle, liver, teeth, and blood.

The second approach uses the radioactive tracer technique. Radioactive fluoride, 18F, is imbibed with water or injected into a vein, and a Geiger counter then records the amount of radiation which emanates from 18F as it passes through the body. Thus, it can be determined exactly where the radioactive fluoride localizes and how much is eliminated. In these experiments, all information must be obtained in about 8-10 hours because of the rapid disin­tegration of 18F, which has a half-life of 1.87 hours as it decays (by loss of a positron) to 180, a stable isotope of oxygen. Radioactive tracer studies were first reported on rats in 1954,2 on sheep in 1955,3 on rats and mice in 1958,4 and on humans in 1960.5 Many similar studies have been carried out subsequently.


In 1945 fluoride balance studies were described on five healthy young men for 28 test periods, each consisting of five eight-hour days. These findings indicated that more than 80% of the fluoride ingested in drinking water was being excreted in urine and perspiration.6 Indeed, sweat is “an important avenue for the elimination of fluoride,” the authors stated”

In a later investigation, the daily diet of nine male ambulatory patients, which averaged 4.4 mg fluoride, was supplemented by 9.1 mg of fluoride (as sodium fluoride).7 Of the total daily amount of fluoride (13.5 mg) thus consumed, 3.6 mg was retained, amounting to 115 mg during the 32-day experimental period. During the 18 days following termination of the experiment, the total amount of excess fluoride excreted in the urine and feces was 9.8 mg, which means that only about 10% of the 115 mg of fluoride retained during the experiment was subsequently eliminated.


Under ordinary conditions fluoride is detectable in the blood stream by 18F tracer within 10 minutes after ingestion and reaches a maximum concentration about 50 minutes later.5 About 47.5% is absorbed through the upper bowels and 25.7% through the stomach wall within one hour by simple diffusion, no active transport mechanism being involved.8 This “normal” course of the metabolic fate of fluoride, however, may be modified considerably by many factors. For instance, when accompanied by calcium, aluminum, magnesium, and phosphates present in food or water, fluoride is absorbed more slowly,9,10 although increased intake of calcium and phosphorus has only a limited effect on the amount that is absorbed.7 Similarly, simultaneous ingestion of fat considerably delays the emptying of the stomach,11 but enhances fluoride absorption into the blood stream.12

When the stomach is unduly acid, as in persons with stomach ulcers, fluoride is more rapidly and more completely absorbed than in a less acid stomach. Once fluoride has reached the lower bowels, little absorption takes place because, in contrast to the acidity of the stomach, the bowel content is alkaline, and some fluoride, instead of entering the blood stream, leaves the body with the fecal material. When fluoride is swallowed with food, tablets, or salt, less of it reaches the blood stream than when taken in water or most other liquids, as with milk, in which the calcium and protein tend to bind fluoride; the absorption is slower and less complete. In an experiment with rats, continuous feeding of fluoride caused greater retention in the body than interrupted feeding.13

In workers and in persons residing close to factories which emit fluoride, however, the respiratory tract is a major route of fluoride ingress. In its gaseous form – essentially hydrogen fluoride – the halogen readily enters the blood stream, mainly in the upper portion of the respiratory tract. The uptake of particulate fluoride compounds is governed mainly by the size of the particles: the larger ones settle in the nose, sinuses, and pharynx and are promptly removed from the body with mucus or swallowed.14 Particles with a diameter of 0.5-5μ will be impacted in the alveolar-capillary bed, the terminal areas of the lungs, where they are absorbed into the blood stream within minutes, especially if they are water soluble.15

In the blood stream between 80% and 90% of the fluoride is present in a “bound” or non diffusible form.16 Most of this fluoride appears to be attached by stable covalent bonds to organic molecules. The rest of the fluoride in blood is in a free, ionic form, the concentration of which reflects both the level of intake and the efficiency of excretion. The “normal” level of serum ionic fluoride, according to D.R. Taves of the University of Rochester, is 0.2-0.4 micromole/liter (μM) or 0.004-0.008 ppm “when the drinking water contains only traces of fluoride, and about 0.5-1 μmol (0.01-0.02 ppm) in a community with fluoridated water.17


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