Dietary calcium does not exacerbate phytate inhibition of zinc absorption by women from conventional diets

Background: Although calcium inhibits zinc bioavailability in rats, especially from high-phytate diets, the effect of calcium on zinc absorption by humans from practical diets remains unclear. Objective: The objective was to test the inhibitory effect of dietary calcium, in Western diets with high and low phytate content, on zinc absorption. Design: Using a 2 x 2 factorial design, zinc absorption was determined in 10 healthy women from 1-d diets with moderate and high calcium contents of approximate to 700 and 1800 mg/d and low and high phytate contents of approximate to 440 and 1800 mg/d. Absorption was measured by using extrinsically added Zn-65 and subsequent whole-body scintillation counting. Results: Mean (+/-SE) fractional zinc absorption was 32.8 +/- 2.3% from the moderate-calcium, low-phytate diet; 26.9 +/- 2.4% from the moderate-calcium, high-phytate diet; 39.4 +/- 2.4% from the high-calcium, low-phytate diet; and 26.2 +/- 2.3% from the high-calcium, high-phytate diet. The respective values for absolute zinc absorption were 3.8 +/- 0.3, 3.0 +/- 0.3, 4.5 +/- 0.3, and 3.2 +/- 0.3 mg/d. Phytate significantly reduced fractional zinc absorption by approximate to 10 percentage points and reduced absolute zinc absorption by 25%, or approximate to 1 mg/d. Differences in dietary calcium did not affect zinc absorption, regardless of a high or low dietary phytate content. Conclusions: In healthy women consuming 1-d menus of ordinary foods (some fortified with calcium), dietary phytate reduces zinc absorption, but calcium does not impair zinc absorption, regardless of whether dietary phytate is low or high. Am J Clin Nutr 2009; 89: 839-43.