Trace minerals are metallic elements required in very small microgram concentrations in the diet. When absorbed they associate with proteins such as enzymes where their ionic charges give shape and structure to the protein component. Without their trace mineral cofactors, the enzymes cannot function as their shape is not correct to bind to substrates and therefore metabolic pathways cease to function, leading to disease and death. Adequate intakes of trace minerals are therefore pivotal to human health. Generally the trace minerals we consume from foods are in highly absorbable forms. This is because as with humans, plants and animals absorb the minerals and they associate with proteins and organic acids. When we eat the animals and plants we consume the trace minerals in their organically associated forms, which are termed chelates. The word chelate is derived from the word for a claw, and it is because the organic molecules surround the metal ion (as a claw) changing its chemical properties in the process.
Natural chelated minerals common in the human diet include iron in haemoglobin, magnesium in chlorophyll, iron in cytochromes and cobalt in the vitamin B12 molecule. Plants chelate minerals to prevent precipitation of the mineral and inhibit its interaction with other metal ions in solution. Plants often bind trace minerals to citric acid, malic acid or amino acids for this purpose. Citrate, malate and amino acid chelated minerals from plants are therefore common in high quality plant based diets. Supplements of trace minerals however can be inorganically bound non-chelated forms of the minerals. The non chelated metal ion form of minerals such as oxides and sulphates are cheap and produced chemically. For example zinc sulfate and zinc oxide are two of the cheapest forms of zinc and are inorganically bound forms of the minerals. When consumed they are much more poorly absorbed compared to organically bound versions of the minerals and they are also much more likely to impede the absorption of other minerals.
The reason for the poor absorption of inorganic forms of minerals is a result of their solubility in the gastrointestinal tract as well as their interaction with strong chelating agents present in many foods. Plants chelate minerals to prevent them precipitating out of solution and to prevent inhibition with other minerals. Protein bound minerals such as the iron in haemoglobin are also highly soluble and the protein (haem) claw prevents the iron interacting with other minerals. When consumed chelated minerals therefore do not interact with other minerals or other food components that could impeded their absorption. Inorganically bound forms of minerals such as sulphates and oxides however, are free to interact with other substances, and in the gut this can include strong chelating agents such as tannins and phytate that bind to the minerals and prevent their absorption. In addition, inorganically bound metal ions can precipitate out of solution in the small intestine, resulting in excretion of the mineral before absorption can occur.
Zinc is an important trace mineral required for normal growth and development. Deficiencies of zinc are common in children in developing countries due to poor access to zinc containing foods. This can impede growth as zinc is required in high concentrations during times of growth. However, in the developed countries, the populations eat poor quality foods that are devoid of meaningful levels of zinc and as a result zinc intakes are low. Supplements could therefore benefit both groups. The absorption of various zinc compounds including zinc citrate, zinc gluconate and zinc oxide has been compared in a randomised trials using healthy adults. The absorption from zinc citrate was 61 %, the absorption from zinc gluconate was 61 %, but the absorption from zinc oxide was 50 %1. While it could be argued that from these results the cheaper zinc oxide is almost as beneficial, taking into account price, it should be remembered that chelated minerals are less likely to interact with other minerals and inhibit their absorption.
Dr Robert Barrington’s Nutritional Recommendation: These results suggest that the organically bound citrate and gluconate forms of zinc are preferential absorbed. As with most things, you tend to get what you pay for, and the cheaper forms of zinc may not be so well absorbed as more expensive organically bound versions of the mineral. Although more expensive, these organically bound forms of zinc are therefore the prefered supplement of choice. The quality of a multivitamin can be judged to some extent on the forms of the minerals they include, with inferior products going for the cheaper inorganically bound minerals. As with all phenomenon, there are exceptions that prove the rule, and magnesium appear to be a case in point. Studies comparing the absorption of organically chelated magnesium with magnesium oxide have shown that the regular inorganic magnesium oxide is just as well absorbed. So in the case of magnesium save your money and get the oxide form if you choose to supplement.
RdB
