Acute effects of iron therapy on zinc status during pregnancy.

The acute effects of iron therapy on zinc status during pregnancy were investigated. The 20 subjects studied were healthy and had unremarkable obstetric histories. The mean stage of gestation was 27 weeks (range 21-33 weeks). Initial hematologic indices (mean +/- SEM) were: hematocrit 36.5 +/- 0.4%, serum ferritin 32.6 +/- 6.1 ng/mL, and serum iron 117 +/- 13 micrograms/dL. Iron therapy, prescribed by the obstetric caregivers, provided a total average daily elemental iron intake of 261 mg (range 164-395 mg) from therapy and routine supplements. Laboratory studies of zinc status were obtained immediately before iron therapy and at one and four weeks thereafter. Initial plasma zinc was 62.9 +/- 2.1 micrograms/dL. A mean decline in plasma zinc of 4.0 +/- 1.8 micrograms/dL (P less than .05) was observed from baseline to one week. The decline remained statistically significant after adjustment for the expected physiologic decline over the same interval of gestation. No further decline occurred from one to four weeks. No significant treatment-related effects were observed for neutrophil zinc, mononuclear leukocyte zinc, or serum alkaline phosphatase activity. These results indicate that iron therapy in doses typically prescribed by obstetric caregivers in this country has an acute, measurable effect on maternal zinc status.