A single 60-mg iron dose decreases zinc absorption in lactating women.

This study determined whether a single 60-mg dose of ferrous sulfate interferes with fractional zinc absorption (FZA) at 7-9 wk of lactation. In a crossover design, 5 exclusively breast-feeding women were given either a single 60-mg iron supplement or no supplement. FZA was measured by analyzing zinc stable isotope tracers ((70)Zn and (67)Zn) in urine samples collected for 7 d after isotope dosing. A 0.7-micromol intravenous (IV) infusion of (70)Zn as ZnCl(2) in saline was followed by a 0.03-mmol oral dose of (67)Zn as ZnCl(2) given with a standardized meal. After a 7-d wash-out period, the supplement given was reversed and a second FZA measurement was taken. FZA was calculated from isotopic enrichments in urine measured by inductively coupled plasma mass spectrometry. Hemoglobin, plasma ferritin and transferrin receptor, and plasma 5'-nucleotidase, plasma zinc and erythrocyte zinc did not differ before the two measurements of zinc absorption. When women were given a single iron supplement, FZA was significantly lower, 21.7 +/- 1.7% compared with 26.9 +/- 2.6% when no supplement was given (P = 0.032). A single 60-mg iron dose significantly decreases FZA during early lactation.

Magnesium, calcium, zinc, and nitrogen loss in trauma patients during continuous renal replacement therapy.

BACKGROUND: Whether standard nutrition support is sufficient to compensate for mineral loss during continuous renal replacement therapy (CRRT) is not known. METHODS: Adult men with traumatic injuries were recruited; one-half of recruits required CRRT for acute renal failure. All urine and effluent (from CRRT) were collected for 72 hours. Urine, effluent, and dialysate were analyzed for magnesium, calcium, and zinc using atomic absorption spectrometry. Urea nitrogen in blood, urine, and effluent were determined by measuring conductivity changes after the addition of urease. Blood was analyzed for magnesium and calcium as part of routine care. Intake was calculated from orders and intake records. RESULTS: Patients receiving CRRT (n = 6) lost 23.9+/-3.1 mmol/d (mean +/- SEM) of magnesium and 69.8+/-2.7 mmol/d of calcium compared with 10.2+/-1.2 mmol/d and 2.9+/-2.5 mmol/d, respectively, lost in patients not in acute renal failure (n = 6; p < .01). Zinc intake was significantly greater than loss in both groups (p < .03). Urea nitrogen excretion did not differ between groups. Serum magnesium was 0.75+/-0.04 mmol/L for CRRT patients, significantly lower than the 0.90+/-0.03 mmol/L for control patients (p < .01). Total blood calcium was below normal in both groups; ionized calcium was below normal in CRRT patients. CONCLUSIONS: CRRT caused significant loss of magnesium and calcium, necessitating administration of more magnesium and calcium than was provided in standard parenteral nutrition formulas. However, additional zinc was not required. CRRT removed amounts of urea nitrogen similar to amounts removed by normally functioning kidneys.