[Elimination of fluoride in urine during fluoridation of salt and drinking water]

From 552 ambulatory gynecological patients in different parts of Switzerland the urinary excretion of fluorine was measured. The patients were classified into 4 groups according to origin: (1) 84 women were from the Canton Basel-Stadt. In this city water has been fluoridated since 1962; (2) 139 women from Canton Glarus. In this area a pilot study was under way using table and baker's salt, to both of which 250 mg F/kg had been added; (3) 128 women from Canton Aargau who were using a low dose fluoridated salt (90 mg F/kg); (4) 201 patients from Cantons Aargau and Tessin respectively who were consuming neither fluoridated water or salt acted as controls. Quantitation of ionized fluorine in urine was performed by means of the fluoride ion sensitive electrode in afternoon urine samples, thus eliminating the influence of sex difference and diurnal rhythm in fluorine excretion. The molar urinary fluorine concentration was related to the corresponding urinary creatinine concentration and expressed as mumol F per mmol creatinine. The fluoridation of salt or water was considered ideal when the excretion factor amounted to 6.29 mumol X mmol-1. The most important finding was that the Glarus females excrete higher levels of fluorine than the patients from Basel, though the difference was no significant. The fluoridation of salt with 90 mg F/kg is followed by an increase of the excretion factor from 2.58 to 3.65 mumol X mmol-1. It could also be demonstrated that in Canton Glarus, where salt with higher fluorine content is used, the excretion coefficient remains below the level believed to be toxic in the long run. It is concluded that salt fluoridation with 250 gm F/kg is safe. Furthermore, the excretion of fluorine in the control group seems to confirm that fluorine is a trace element of ubiquitous occurrence even excreted in urine of individuals who deliberately avoid fluorine as an additive to table salt or water.