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 approximately 700 and 1800 mg/d and low and high phytate contents of approximately 440 and 1800 mg/d. Absorption was measured by using extrinsically added (65)Zn 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 approximately 10 percentage points and reduced absolute zinc absorption by 25%, or approximately 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.