The short-term effect of calcium supplements (1200 mg Ca/d) on daily nonheme-iron absorption was measured in 14 healthy adult volunteers by using stable isotope extrinsic labeling and fecal monitoring techniques. Mean (+/- SEM) nonheme-iron absorption from a low-calcium (< 320 mg/d), moderately high-iron (15 mg/d) diet was 15.8 +/- 2.1%, but in the presence of calcium (400 mg/meal) as calcium carbonate, absorption fell significantly to 4.7 +/- 1.4% (P < 0.001). The long-term effect of consuming calcium supplements with meals (1200 mg Ca/d) on body iron (functional and storage iron) was investigated in 11 iron-replete adults over a 6-mo period. An unsupplemented control group (n = 13) was also monitored to correct for any seasonal changes in the biochemical measurements. There were no changes in any of the hematologic indexes, including hemoglobin, hematocrit, zinc protoporphyrin, and plasma ferritin resulting from the calcium supplementation. The results clearly show that long-term supplementation with calcium did not reduce plasma ferritin concentrations in iron-replete adults consuming a Western-style diet containing moderate to high amounts of calcium in most meals.