Nutritional implications of the interactions between minerals

It is well recognized that the absorption, retention and metabolism of most essential minerals can be markedly influenced by the presence of antinutrient factors in the diet (i.e. fiber and phytate). However, in addition, interactions can also occur between essential minerals. Indeed, under some circumstances, these interactions can be profound and have significant implications for human health. Interactions between essential minerals can be broadly classified as direct or indirect. Direct interactions are generally competitive phenomena that occur during the intestinal absorption and/or during the tissue utilization of a mineral. Indirect interactions occur when one of the minerals is involved in the metabolism of the other mineral, or when a deficiency or toxicity of one of the minerals results in hormonal changes or tissue damage which affects the metabolism of the other mineral. In this review we have focused our comments on direct interactions between essential minerals, and we present suggested levels at which an excess of a mineral (coined "X") can significantly alter the metabolism of another mineral (coined "Y") for several of the known competitive interactions. This level is characterized as the lowest X/Y ratio of the dietary intakes which has been shown to produce negative consequences on the metabolism of the element Y (assuming the intake of Y is physiological). Moreover, the importance of the physiological status of the animal with regard to the determination of these ratios is discussed. The calculated X/Y ratio at which interactions may be predicted to occur is generally higher than the ratio calculated for most minerals using typical dietary intakes of X and Y in Western-type diets. However, ratios which might be predicted to result in negative interactions do occur in select food products, and can be reached as a consequence of supplementation (either through food enrichment or therapeutic use of supplements). In fact, considering the ready availability of dietary supplements, such interactions may become commonplace. Finally, the interactions between essential and non-essential minerals (heavy metals) are briefly discussed, as are indirect mineral interactions.