Aqueous solutions of NaF and sodium monofluorophosphate (MFP) were given to fasting young adults in an intra-individual cross-over study. Plasma fluoride (F) levels were measured by use of a F-ion-sensitive electrode, and eight-hour profiles of F concentrations in plasma were determined. F availability and pharmacokinetic data were identical for both substances. Furthermore, the same subjects were given tablets containing 2 mg F, either as NaF or as MFP, under different experimental regimens: (a) on a fasting stomach, (b) together with milk, or (c) together with breakfast and milk. Equal F availabilities were observed for both substances. Plasma peak levels were reduced when the tablets were taken together with food. Intake of milk reduced F availability by 30% compared with the fasting stomach experiment; this effect was abolished when milk was taken as part of the breakfast. It is suggested that formation of Ca salts and entrapment of F in coagulation products of milk are important factors causing reduction of F availability, and that prolonged stay of the chyme after concomitant ingestion of food allows F to become liberated from bound forms and coagulation products by digestion processes.

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A survey was made of the fluoride content of selected human foods, some animal feeds, and related materials, with the purpose of a better characterization of products whose fluoride may contribute to the intake of fluoride by man as well as by some kinds of animals. Uptake of fluoride, especially from food with or without a foregoing food chain, was found to be more widely spread than has been documented previously. The major source of fluoride is represented by marine organisms, regardless of the ways by which man or animals are exposed to fluoride. As a consequence of the detailed analytical data given, recommendations would extend towards i) a more wide-spread analytical control of foods and feeds for fluoride, ii) an intensified assessment of fluoride bioavailabilities from foods and feeds, and iii) the consideration of such data in the evaluation of fluoride supplementations for optimized intakes, as recommended.

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