Conflicting evidence of iron and zinc interactions in humans: does iron affect zinc absorption?

Department of Biochemistry
Armed Forces Medical College
Pune, 411 040
India
E-mail: sbodiga@yahoo.com

Dear Sir:

This letter is in reference to the article by Lind et al (1) on iron and zinc supplementation in infants that appeared in a recent issue of the Journal. I understand that the importance of the interactive effects of trace elements, particularly iron and zinc, on nutrient requirements is increasingly being recognized. The coexistence of multiple micronutrient deficiencies is a widespread public health problem in many regions of the world. Earlier human studies (2–7) provided evidence in favor of iron and zinc interactions at the site of absorption but gave conflicting results that were probably due to variations in protocol design or in the trace element status of subjects before the experiment.

The study by Lind et al was conducted in the same major population as that reported on earlier by Dijkhuizen et al (2)—ie, Indonesian infants < 1 y old. It also used the same doses of iron (10 mg) and zinc (10 mg), and supplementation was provided over the same span of time. Rates of prevalence of anemia, iron deficiency, and reduced serum zinc concentrations were the same as those reported for this population by Dijkhuizen et al. Lind et al reported that there was a significant dose effect on serum zinc in the group supplemented with zinc alone, which indicated a negative effect of iron on zinc absorption. This finding does not agree with the observation of Dijkhuizen et al that iron supplementation does not depress serum zinc concentrations. What could be the reason for these conflicting results when the study by Lind et al seems to have no confounding variables compared with the study by Dijkhuizen et al? Both of these studies concluded that concurrent supplementation with iron and zinc is less efficacious in improving the iron and zinc status than is supplementation with either iron or zinc alone, but can single supplements promote catch-up growth in a stunted and wasted population, or must we look for any other limiting variables to explain these differences?

REFERENCES

1. Lind T, Lönnerdal B, Stenlund H, et al. A community-based randomized controlled trial of iron and zinc supplementation in Indonesian infants: interactions between iron and zinc. Am J Clin Nutr 2003;77:883–90.
2. Dijkhuizen MA, Wieringa FT, West CE, Martuti S, Muhilal. Effects of iron and zinc supplementation in Indonesian infants on micronutrient status and growth. J Nutr 2001;131:2860–5.
3. Donangelo CM, Woodhouse LR, King SM, Viteri FE, King JC. Supplemental zinc lowers measures of iron status in young women with low iron reserves. J Nutr 2002;132:1860–4.
4. Peres JM, Bureau F, Neuville D, Arhan P, Bougle D. Inhibition of zinc absorption by iron depends on their ratio. J Trace Elem Med Biol 2001;15:237–41.
5. Bougle D, Proust A. Iron and zinc supplementation during pregnancy: interactions and requirements. Contracept Fertil Sex 1999;27:537–43.
6. Friel JK, Serfass RE, Fennessey PV, et al. Elevated intakes of zinc in infant formulas do not interfere with iron absorption in premature infants. J Pediatr Gastroenterol Nutr 1998;27:312–6.
7. Solomons NW. Competitive interactions of iron and zinc in the diet: consequences for human nutrition. J Nutr 1986;116:927–35.