Effect of level and form of phosphorus and level of calcium intake on zinc, iron and copper bioavailability in man

Abstract

A 75-day human metabolic study was conducted to evaluate the effects of 1 g supplements of phosphorus, either as orthophosphate or hexametaphosphate, alone and in combination with 810 mg calcium on zinc, iron and copper bioavailability in ten young men. An additional objective was to determine the effects of increasing dietary calcium on polyphosphate hydrolysis. All subjects consumed each of the five diets (basal, low calcium-high orthophosphate, low calcium-high polyphosphate, high calcium-high orthophosphate and high calcium-high polyphosphate) for 15 days. Increasing dietary calcium caused a significant decrease in polyphosphate hydrolysis; the calcium supplement stabilized hexametaphosphate and all of its' polyphosphate hydrolysis products except pyrophosphate. Both phosphate supplements caused significant decreases in iron absorption and retention at the lower level of calcium intake, but the hexametaphosphate exerted a substantially greater effect. Simultaneously supplementing the diet with calcium and orthophosphate caused a similar reduction in iron absorption and retention to that found at the lower level of calcium intake. The hexametaphosphate supplement was without significant effect on iron absorption and retention at the higher level of calcium intake, and caused a significant decrease in copper retention. Zinc retention was not significantly affected by any dietary treatment.