Giving children combined iron-zinc supplements may be less effective in preventing deficiencies of the minerals than individual supplementation, report Swedish researchers this month.
The study, performed in Indonesia and led by T Lind of the Department of Public Health and Clinical Medicine at the University of Umea, Sweden, aimed to compare the effect in infants of combined supplementation with iron and zinc and supplementation with single micronutrients on iron and zinc status.
Nearly 700 infants were randomly assigned to daily supplementation of either 10mg iron, 10mg zinc, a combination of 10mg iron and 10mg zinc, or placebo from six to 12 months of age.
Blood samples were collected at the start and end of the study. A total of 549 infants completed the supplementation and both baseline and follow-up blood samples were available for analysis.
Baseline prevalences of anaemia, iron deficiency anaemia (anaemia and low serum ferritin) and low serum zinc were recorded as 41 per cent, 8 per cent, and 78 per cent, respectively. After supplementation, the researchers reported higher haemoglobin (119.4 compared with 115.3 g/L) and serum ferritin (46.5 compared with 32.3 µg/L) values for the Iron group than for the Iron and Zinc group. The researchers considered this as evidence of an effect of zinc on iron absorption.
As expected, the zinc group had higher serum zinc levels (11.58 compared with 9.06 µmol/L) than did the placebo group. According to the researchers there was also a dose effect on serum ferritin in the Iron and Iron and Zinc groups, but at different levels. There was a significant dose effect on serum zinc in the Zinc group, whereas no dose effect was found in the Iron and Zinc group beyond 7 mg of daily zinc intake.
The researchers concluded that supplements of iron and zinc together may be less effective than single supplements in improving iron and zinc status among infants. They suggest that the interaction between iron and zinc decreases the effects of a combined supplement.
Full details of the study can be found in the April 2003 edition of the American Journal of Clinical Nutrition.