Effects of calcium supplements on oral bioavailability of fluoride in soil based on In Vivo and In Vitro methods

Dietary calcium (Ca) intake can alleviate fluoride (F) induced fluorosis to maintain bone health. However, it is unclear whether calcium supplements can reduce the oral bioavailability of F present in contaminated soils. Here we evaluated the effects of Ca supplements on F bioavailability in three soils using an in vitro method (Physiologically Based Extraction Test) and an in vivo mouse model. Seven Ca salts, commonly used in calcium supplements, significantly reduced the F bioaccessibility in the gastric and small intestinal phases. Particularly for Ca phosphate at 150 mg Ca supplementation, F bioaccessibility in the small intestinal phase was reduced from 35.1-38.8% to 0.7-1.9% where soluble F concentrations were less than 1 mg/L. Overall, the eight Ca tablets tested in this study showed greater efficiency at decreasing F solubility. The in vitro bioaccessibility after Ca supplementation was consistent with the relative bioavailability of F. As supported by X-ray photoelectron spectroscopy, a possible mechanism is that freed F can be bound by Ca to form insoluble CaF2 and exchanged with OH groups from Al/Fe hydroxide to strongly adsorb F. These findings provide evidence of Ca supplementation in reducing health risks associated soil F exposure.