The fluorine contenit of urine specimens of a large number of men and boys has been studied in relation to fluorine in their domestic water supplies. Where domestic waters are free of fluorine, the fluorine present in urine averages 0.3 to 0.5 p.p.m. An increase of fluorine in urine was associated with the use of domestic waters containing as little as 0.5 p.p.m. fluorine. Fluorine in urine specimens continues strikingly proportional to the fluorine content of the drinking water through the range of 0.5 to 5.1 p.p.m. fluorine in the domestic water. The results appear to furnish additional evidence of the importance of water-borne fluorine as a source of fluorine in human diets. The data agree with previous epidemiological studies which have demonstrated a striking relation between fluorine in communal water supplies and dental health, including reduced incidence of dental caries in 12- to 14-year-old children.
The close correlation between fluorine in drinking water and fluorine content of urine suggests that the presumed hazard of cumulative toxic bone-fluorosis surrounding certain water-borne sources of fluorine in the United States is greatly reduced by this relationship. An efficient urinary elimination of fluorine appears to be characteristic of individuals residing in certain fluoride areas of the United States, where the drinking water contains 0.5 to 5.0 p. p. m. fluorine. The metabolism of fluorine under these conditions seems to be a normal function of the lhuman body and seems characterized by a condition approaching metabolic equilibrium, at least in the adult organism.