Micronutrient interactions: effects on absorption and bioavailability.

A potential risk of interactions between micronutrients affecting absorption and bioavailability has to be considered in any supplementation or fortification strategy. At levels of essential micronutrients present in foods, most micronutrients appear to utilise specific absorptive mechanisms and not be vulnerable to interactions. In aqueous solutions and at higher intake levels competition between elements with similar chemical characteristics and uptake by non-regulated processes can take place. These interactions have clearly been demonstrated in experimental absorption studies and to some extent have been confirmed in supplementation studies. Negative effects of iron supplementation on indices of zinc and copper status and of zinc supplementation on iron and copper status have been reported. In contrast, the negative effect of calcium on iron absorption has not been confirmed in long-term supplementation studies. Ascorbic acid has a strong iron absorption promoting potential and in iron deficient populations ascorbic acid supplementation improves iron status. Thus, ascorbic acid supplements or an increased intake of ascorbic acid rich foods could have important public health implications, especially in populations subsisting on a mainly plant food based diet. The effect of poor status of a given micronutrient on absorption and utilisation of other micronutrients should also be considered while developing strategies to improve micronutrient status in a population. Awareness of these interactions, combined with a balanced evaluation of the dietary intake of the population with regard to absorption promoting and inhibiting substances and the risk for multiple deficiencies, could lead to more effective strategies to improve micronutrient status.