Dietary minerals are inorganic elements that are required by humans for particular metabolic needs. Many of the functions of minerals in humans are as cofactors to enzymes, although some are required for structural reasons or as electrolytes. Examples of minerals that act as cofactors to enzymes include zinc, copper, iron, selenium and manganese. Examples of minerals that are used structurally include calcium, magnesium, phosphorus and boron. Examples of minerals that function as electrolytes include calcium, magnesium, chloride and potassium. Deficiencies of minerals lead to specific mineral deficiency diseases, and some of these have been well characterised in animals and human studies. However, there still exists a chasm in the understanding of chronic suboptimal levels of minerals in humans due to the ethical difficulty in studying this sort of problem. The association between mineral deficiencies and cancer has therefore been slow to be constructed and even now controversy exists in this field.
The association between certain minerals and cancer has been quite well established. Selenium deficiency for example is known to be associated with an increased risk of cancer. Further, it is known that selenium is required as a cofactor in the enzyme glutathione peroxidase, and this enzyme plays an important role in the inhibition of oxidative stress in cells. As oxidative stress is involved in the aetiology of cancer, a mechanisms is known to exist by which selenium could mechanistically protect from cancer. Zinc is also a cofactor in an antioxidant enzyme, the superoxide dismutase system. Although The superoxide dismutase system has not been as extensively studies as the glutathione peroxidase system with respect to cancer, they do play an overlapping, although admittedly distinct, role in preventing oxidative stress in cells. Evidence suggests that diets high in zinc are protective of cancer, and mechanistically this could be explained by the role of zinc in the superoxide dismutase system of antioxidant defences.
Dietary calcium is also associated with a reduced risk of cancer. Mechanistically it would be harder to explain how calcium intake may have a causative effect against cancer. Of course, it may be that a high calcium intake is simply a marker of a healthy diet, and the same could be said for the association between the mineral zinc and the risk of cancer. Generally those that eat higher quality diets have higher intakes of micronutrients including calcium and zinc, and it may therefore be other factors in the diet that are the cause of the reduced risk of cancer. Calcium for example is high in plant foods and high calcium intakes may symbolise high plant diets that are known to be protective of cancer. Likewise high dairy diets contain high amounts of calcium, and are also rich in conjugated linoleic acid which is known to have anti-cancer effects. Whether calcium has direct anti-cancer effects is therefore yet to be established, but high quality diets containing high intakes of minerals are certainly associated with cancer protection.
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