PHYTIC ACID PLUS SUPPLEMENTAL CALCIUM, BUT NOT PHYTIC ACID ALONE, DECREASES FLUORIDE BIOAVAILABILITY IN THE RAT

Results of in vitro studies have suggested that fluoride becomes insoluble when some soy-based infant formulas are diluted with fluoridated water because of the presence of phytate, added calcium, or a combination of these factors. The present study was designed to test this hypothesis in vivo. Male albino rats (25 days old) were fed a purified diet containing phytic acid (0 or 6.06 mmol/kg), calcium (125 or 250 mmol/kg) and fluoride (526-mu-mol/kg) for 4 weeks in a factorial design of treatments. Phytic acid was added to the diet by chemically reacting a phytic acid concentrate with casein prior to diet preparation to mimic a soy protein. Food intake, weight gain, and femur phosphorus were unaffected by dietary treatments. Both phytic acid and supplemental calcium alone had little or no effect on fluoride uptake into either bone or teeth. The combination of phytic acid plus supplemental calcium, however, significantly increased percent of fluoride intake found in the feces, which was reflected in a significant decrease (20%) in fluoride concentration of femur, second molar teeth, and vertebrate bone. These results provide evidence that insoluble complex formation produced by a calcium and phytate interaction can explain reduced fluoride solubility in some soy-based infant formulas as well as decreased fluoride absorbability in vivo.