Minerals are inorganic substances required by the body in small amounts for a variety of functions. These include the formation of bones and teeth; as essential constituents of body fluids and tissues; as components of enzyme systems and for normal nerve function.
Some minerals are needed in larger amounts than others, e.g. calcium, phosphorus, magnesium, sodium, potassium and chloride. Others are required in smaller quantities and are sometimes called trace minerals, e.g. iron, zinc, iodine, fluoride, selenium and copper. Despite being required in smaller amounts, trace minerals are no less important than other minerals.
Minerals are often absorbed more efficiently by the body if supplied in foods rather than as supplements. Also, a diet that is short in one mineral may well be low in others, and so the first step in dealing with this is to review and improve the diet as a whole. Eating a varied diet will help ensure an adequate supply of most minerals for healthy people.
Most people do not show signs of deficiency but this does not mean their intakes or nutrient status are adequate. For example, adolescent girls, women of childbearing age and some vegans/vegetarians are more susceptible to low iron status as their dietary intake may not match their requirements, and therefore they are at risk of iron deficiency anaemia. There is also concern about the calcium intake of some adolescents, and young and older women and the implications for future bone health.
Certain groups of people may have higher requirements for specific minerals, e.g. women with particularly heavy periods may need extra iron, and extra calcium (and vitamin D) is sometimes recommended by doctors for women at high risk of osteoporosis. In such cases, supplements may be useful but should not replace a varied and healthy diet.
The bioavailability of a mineral (i.e. how readily it can be absorbed and used by the body) may be influenced by a variety of factors. Bioavailability will depend upon the chemical form of the mineral, other substances present in the diet and (for nutrients such as iron) the individual person’s needs as determined by how much of the nutrient is already stored in the body. This is because the body has sensitive mechanisms for preventing storage of nutrients that can be damaging in excess (as is the case with iron).
Some dietary constituents reduce bioavailability. Phytate, for example, found in products made from wholegrain cereals (especially unleavened breads such as chapattis) can bind and hence reduce the absorption of calcium, iron and zinc. Iodine absorption may be hindered by nitrates. Similarly, oxalate present in spinach and rhubarb binds any calcium present, making it unavailable for absorption. Also an excess of one mineral may hinder the absorption of another by competing for the same transport systems in the gut, e.g. excess iron reduces zinc absorption. This generally only becomes a problem when zinc intakes are already marginal.
Unlike some vitamins, minerals are fairly stable in normal food processing and storage conditions.