The effect of long-term calcium supplementation on indices of iron, zinc and magnesium status in lactating Gambian women

Abstract

The effect of long-term supplementation with CaCO3 on indices of Fe, Zn and Mg status was investigated in a randomized, double-blind intervention study of sixty lactating Gambian women. The supplement contained 1000 mg Ca and was consumed between meals 5 d/week, for 1 year starting 1.5 weeks postpartum. Compliance was 100%. Plasma ferritin concentration, plasma Zn concentration and urinary Mg output were measured before, during and after supplementation at 1.5, 13, 52 and 78 weeks postpartum. No significant differences in mineral status were observed at any time between women in the supplement and placebo groups. Analysis of the longitudinal data series showed that plasma ferritin and Mg excretion were characteristic of the individual (P < 0.001). Within individuals, ferritin concentration was higher at 1.5 weeks postpartum than later in lactation (P = 0.002). Plasma Zn concentration was lower at 1.5 weeks postpartum than at other times (P < 0.001), an effect which disappeared after albumin correction. Low plasma concentrations of ferritin and Zn indicated that the Gambian women were at high risk of Fe and Zn deficiency. Measurements of alpha 1-antichymotrypsin suggested that the results were not confounded by acute-phase responses. The results of the present study indicate that 1000 mg Ca as CaCO3 given between meals does not deleteriously affect plasma ferritin and Zn concentrations or urinary Mg excretion in women who are at risk of Fe and Zn deficiency.

PIP: During March 1990-March 1991, 60 lactating mothers were recruited into a randomized, placebo-controlled trial designed to examine the effect of calcium (Ca) supplementation on plasma zinc (Zn) and ferritin (Fe) concentrations and on magnesium (Mg) excretion during and after Ca supplementation. The women lived in Keneba and Manduar villages in rural Gambia. They consumed 1000 mg Ca or the placebo (2 tablets of dextrose) between meals 5 days/week for 12 months beginning 1-5 weeks postpartum. All women complied. At no time were there significant differences in the indices used to determine Zn, Fe, and Mg status between lactating women on Ca supplements and those receiving the placebo. In fact, the mean differences were less than 10% of the total value. Many women (33-50%), regardless of supplementation group, had a plasma Fe concentration lower than 12 mcg/l, indicating depleted Fe stores. Many women also had low plasma Zn levels. Within individuals, plasma Zn concentrations were 15% lower at day 9 than later in lactation (p 0.001), while plasma Fe levels were 10% higher (p = 0.002). Plasma Zn levels were associated with plasma albumin levels (p 0.001). When adjusted for albumin, the effect of lactation on Zn disappeared. When compared with British women, Gambian women had a lower plasma Zn concentration (p 0.001). Within individuals and after adjustment for lactation stage and for albumin, plasma Zn levels varied between seasons (i.e., hot season values higher than other seasons) (p = 0.004). Women were more likely to excrete Mg during the hot season (p 0.001). These findings indicate that ingestion of 1000 mg Ca between meals has no adverse effect on plasma Fe and Zn levels or urinary Mg excretion in women at risk of Zn and Fe deficiency.