Influence of Milk and Food on Fluoride Bioavailability from NaF and Na2FPO 3 in Man

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.