Minerals C. Reilly, Oxford Brookes Universit 4.1 Introduction Minerals are the inorganic elements, other than carbon, hydrogen, oxygen and nitrogen, which remain behind in the ash when food is incinerated. They are usually divided into two groups- macrominerals and microminerals(or trace elements). The terms are historical in origin and originated at a time when the development of analytical equipment was still in its infancy and trace'was used to refer to components whose presence could be detected, but not quantified. Modern analytical equipment that allows determination of elements at levels in the nano- and even picogram range, can show the presence of most of the minerals in almost any food. Some are present in minute amounts, but others are at significant levels The minerals are classified as either essential or non-essential g on hether or not they are required for human nutrition and have metabolic roles in the body. Non-essential elements are also categorised as either toxic or non-toxic. Table 4.1 lists elements that occur in food and are important in human nutrition In addition to the essential elements. some others including arsenic, silicon and boron, have been shown to be required by certain animals and may also play beneficial roles in the human body This section will present an overview of the principal essential minerals, cov ring their chemical characteristics, basic roles in human health, dietary origins (from food and supplements), and their Reference Nutrient Intakes(RND), includ ing Safe Intakes (SI). This will be followed by consideration of a number of selected minerals that are of particular interest at the present time. Attention will be given particularly to their nutritional significance, including their possible roles as functional ingredients of food. The elements to be discussed in detail are
4 Minerals C. Reilly, Oxford Brookes University 4.1 Introduction Minerals are the inorganic elements, other than carbon, hydrogen, oxygen and nitrogen, which remain behind in the ash when food is incinerated. They are usually divided into two groups – macrominerals and microminerals (or trace elements). The terms are historical in origin and originated at a time when the development of analytical equipment was still in its infancy and ‘trace’ was used to refer to components whose presence could be detected, but not quantified. Modern analytical equipment that allows determination of elements at levels in the nano- and even picogram range, can show the presence of most of the minerals in almost any food. Some are present in minute amounts, but others are at significant levels. The minerals are classified as either essential or non-essential, depending on whether or not they are required for human nutrition and have metabolic roles in the body. Non-essential elements are also categorised as either toxic or non-toxic. Table 4.1 lists elements that occur in food and are important in human nutrition. In addition to the essential elements, some others, including arsenic, silicon and boron, have been shown to be required by certain animals and may also play beneficial roles in the human body. This section will present an overview of the principal essential minerals, covering their chemical characteristics, basic roles in human health, dietary origins (from food and supplements), and their Reference Nutrient Intakes (RNI), including Safe Intakes (SI). This will be followed by consideration of a number of selected minerals that are of particular interest at the present time. Attention will be given particularly to their nutritional significance, including their possible roles as functional ingredients of food. The elements to be discussed in detail are
98 The nutrition handbook for food processors Table 4.1 Mineral elements in food Macrominerals (g/kg) Microminerals(mg/kg) Tox als(mg/kg) Calcium(<1-12) chromium(<0.02-0.95) Cadmiun(0.001-0.07) Magnesium (1-4) Cobalt(0.008-0.32) Lead(0.01-0.25) Phosphorus (1-6) Copper(<0.2-3.3) Mercury(<0001-0.18) Potassium(1-6) dine00.040 Sodium(1-19) Iron(<0.2-92) Manganese(<. 10-14.0) Molybdenum(0.004-1. 29) Selenium(<0.001-0.34) Zinc(0.2-8.6) data from Reilly C (2002) Metal Contamination of Food, 3rd ed Blackwell sc Oxford calcium, iron, and zinc. two other elements, iodine and selenium, will also be considered, though in less detail. A final section will provide suggestions for further reading 4.2 Chemical characteristics Nearly all the minerals required by the body are elements of low atomic number, from sodium(11) to selenium(34); the exceptions are molybdenum(42)and iodine(53). In living matter, these elements are present in a number of different states: as inorganic compounds, as free ions in body fluids, or combined with organic compounds( Coultate, 1985) Approximately 99%o of the bodys calcium and 85% of its phosphorus are in the hard mineral component of bone. The two elements are combined together to form a compound similar to hydroxyapatite, CaIo(OH)(PO4). Other inorganic elements, such as fluoride(F), magnesium sodium and potassium are also incor- porated into the bone mineral to form the partly amorphous and partly crystalline structure of bone In contrast to calcium in the skeleton, the element iron occurs almost entirely part of co-ordination compounds based on the porphyrin nucleus involved in he transport of oxygen. Several of the other trace elements are also mainly present in biological tissues as organic compounds, such as selenium in the met- alloenzyme glutathione peroxidase, and molybdenum in superoxide dismutase 4.3 Impact on health, absorption and recommended intakes Minerals function mainly in three ways in the bod 1. As structural components, e.g. calcium, phosphate and magnesium in bones and teeth
calcium, iron, and zinc. Two other elements, iodine and selenium, will also be considered, though in less detail. A final section will provide suggestions for further reading. 4.2 Chemical characteristics Nearly all the minerals required by the body are elements of low atomic number, from sodium (11) to selenium (34); the exceptions are molybdenum (42) and iodine (53). In living matter, these elements are present in a number of different states: as inorganic compounds, as free ions in body fluids, or combined with organic compounds (Coultate, 1985). Approximately 99% of the body’s calcium and 85% of its phosphorus are in the hard mineral component of bone. The two elements are combined together to form a compound similar to hydroxyapatite, Ca10(OH)2(PO4)6. Other inorganic elements, such as fluoride (F- ), magnesium sodium and potassium are also incorporated into the bone mineral to form the partly amorphous and partly crystalline structure of bone. In contrast to calcium in the skeleton, the element iron occurs almost entirely as part of co-ordination compounds based on the porphyrin nucleus involved in the transport of oxygen. Several of the other trace elements are also mainly present in biological tissues as organic compounds, such as selenium in the metalloenzyme glutathione peroxidase, and molybdenum in superoxide dismutase. 4.3 Impact on health, absorption and recommended intakes Minerals function mainly in three ways in the body: 1. As structural components, e.g. calcium, phosphate and magnesium in bones and teeth. 98 The nutrition handbook for food processors Table 4.1 Mineral elements in food Macrominerals (g/kg) Microminerals (mg/kg) Toxic minerals (mg/kg) Calcium (<1–12) Chromium (<0.02–0.95) Cadmium (0.001–0.07) Magnesium (1–4) Cobalt (0.008–0.32) Lead (0.01–0.25) Phosphorus (1–6) Copper (<0.2–3.3) Mercury (<0.001–0.18) Potassium (1–6) Iodine (0.04–0.66) Sodium (1–19) Iron (<0.2–92) Sulphur (<2–6) Manganese (<0.10–14.0) Molybdenum (0.004–1.29) Selenium (<0.001–0.34) Zinc (0.2–8.6) data from Reilly C (2002) Metal Contamination of Food, 3rd ed. Blackwell science: Oxford
Minerals 99 2. In organic combinations as physiologically important compounds, e. g phos- phorus in nucelotides, zinc in enzymes such as carbonic anhydrase, iodine in thyroid hormone. 3. In solution in body fluids to maintain pH, help conduct nerve impulses control muscle contraction, e.g. sodium and potassium in blood and intra cellular fluids The macrominerals are mainly involved in functions I and 3, and the micromin- erals in function 2 A normal diet, composed of a mixture of both plant and animal foodstuffs, should supply all the minerals required by the body. When such a diet is not avail- ble, or in some other situations, it may be necessary to provide the missing ele ments in the form of supplements or by fortifying the diet with additional minerals. The minerals ingested in food are absorbed after digestion from the gut nto the blood stream, which transports them to the sites where they function or are stored. Not all minerals are absorbed to the same extent. Some includin sodium and potassium, are readily absorbed as ions or as simple compound Others, such as calcium, magnesium and phosphorus may be combined as indi- gestible or insoluble compounds in food and are less easily taken up from the gut. A few others, especially some of the trace elements such as iron, are poorly absorbed Uptake of certain minerals from food can be affected by other components of the diet. Thus phytic acid and phytates in cereals can inhibit absorption of iron nd zinc. The same effect can be caused by oxalate in certain vegetables. lodine absorption can be limited by sulphur-containing compounds known as goitrogens which occur in certain plants, such as some brassicae and cassava. Consumption of these vegetables can acerbate iodine deficiency and increase the likelihood of If an essential element is at a low level in the diet, a nutritional deficiency may ccur,with specific symptoms. Thus an inadequate intake of iron can cause anaemia when there is insufficient haemoglobin to meet the needs of the body for oxygen transport. A deficiency of iodine can lead to goitre when the body tries to compensate for a low production of the iodine-containing thyroid hormone by increasing the size of the thyroid gland. Inadequate zinc may result in growth failure in children. Usually these conditions are corrected when intake of the missing element is increased by improving the diet or by providing An excessive intake of a mineral may also have serious consequences for health. Too much sodium in the diet may be associated with high blood pressure and increased risk of a stroke. A condition known as siderosis. in which an excess of iron is deposited in the body, can result when too much iron is absorbed. Selenosis. a sometimes fatal effect of an excessive intake of selenium is known to occur in parts of China where high levels of the element enter locally grown foods from selenium-rich soil. Less serious effects such as nausea, can be caused by a high intake of zinc
2. In organic combinations as physiologically important compounds, e.g. phosphorus in nucelotides, zinc in enzymes such as carbonic anhydrase, iodine in thyroid hormone. 3. In solution in body fluids to maintain pH, help conduct nerve impulses, control muscle contraction, e.g. sodium and potassium in blood and intracellular fluids. The macrominerals are mainly involved in functions 1 and 3, and the microminerals in function 2. A normal diet, composed of a mixture of both plant and animal foodstuffs, should supply all the minerals required by the body. When such a diet is not available, or in some other situations, it may be necessary to provide the missing elements in the form of supplements or by fortifying the diet with additional minerals. The minerals ingested in food are absorbed after digestion from the gut into the blood stream, which transports them to the sites where they function or are stored. Not all minerals are absorbed to the same extent. Some, including sodium and potassium, are readily absorbed as ions or as simple compounds. Others, such as calcium, magnesium and phosphorus may be combined as indigestible or insoluble compounds in food and are less easily taken up from the gut. A few others, especially some of the trace elements such as iron, are poorly absorbed. Uptake of certain minerals from food can be affected by other components of the diet. Thus phytic acid and phytates in cereals can inhibit absorption of iron and zinc. The same effect can be caused by oxalate in certain vegetables. Iodine absorption can be limited by sulphur-containing compounds known as goitrogens, which occur in certain plants, such as some brassicae and cassava. Consumption of these vegetables can acerbate iodine deficiency and increase the likelihood of goitre. If an essential element is at a low level in the diet, a nutritional deficiency may occur, with specific symptoms. Thus an inadequate intake of iron can cause anaemia when there is insufficient haemoglobin to meet the needs of the body for oxygen transport. A deficiency of iodine can lead to goitre when the body tries to compensate for a low production of the iodine-containing thyroid hormone by increasing the size of the thyroid gland. Inadequate zinc may result in growth failure in children. Usually these conditions are corrected when intake of the missing element is increased by improving the diet or by providing supplements. An excessive intake of a mineral may also have serious consequences for health. Too much sodium in the diet may be associated with high blood pressure and increased risk of a stroke. A condition known as siderosis, in which an excess of iron is deposited in the body, can result when too much iron is absorbed. Selenosis, a sometimes fatal effect of an excessive intake of selenium is known to occur in parts of China where high levels of the element enter locally grown foods from selenium-rich soil. Less serious effects, such as nausea, can be caused by a high intake of zinc. Minerals 99
100 The nutrition handbook for food processo Table 4.2 Reference nutrient intakes and safe intakes for minerals Mineral male(19-50 years) female(19-50 years) Calcium(RND mg/day 70 Phosphorus(RND) mg/day 550 Potassium(RND) mg/day 3500 Chloride(RND) mg/day 635 Iron(RNi) mg/day 14.8+ 7.0 Copper(RNi)mg/day Selenium(RND) ug/day lodine(RND) ug/day Manganese(SI) mg/day above 1. 4 Molybdenum(SI) ug/day chromium(SD) ug/ above Fluoride(si) mg/kg body weight/day insufficient for women with high menstrual losses where the most practical way of meeting iron requirements is to take iron supplements dapted from Department of Health(1991) Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. HMSO: London Health authorities in most countries have established recommendation for intake levels of essential minerals which both meet the nutritional requirements of consumers and at the same time prevent excessive intakes. In the UK, Refer- ence Nutrient Intakes(RND) for 1l minerals have been published by the Depart- ment of Health to meet the requirements for the different age groups and sexes in the Community(Department of Health, 1991). The RNI is defined as an amount of the nutrient that is enough, or more than enough, for about 97 per cent of people in a group. In addition Safe Intakes (SI) have been established for another four minerals. The si is'a term used to indicate intake or range of intakes of a nutrient for which there is not enough information to estimate rNi..it n amount that is enough for almost everyone but not so large as to cause unde sirable effects. The RNI for minerals for adult men and women are given in Table 4.4 Dietary sources, supplementation and fortification Because our food is almost entirely made up of components that were once parts of living organisms and since there is a broad similarity between the nutritional requirements and cellular biochemistry of most forms of animal and plant life, it is to be expected that our needs for the mineral nutrients will be met by a con- entional mixed diet( Coultate, 1985). It is usually only in exceptional situations, ple, there is a reliance on locally produced food in an area where
Health authorities in most countries have established recommendation for intake levels of essential minerals which both meet the nutritional requirements of consumers and at the same time prevent excessive intakes. In the UK, Reference Nutrient Intakes (RNI) for 11 minerals have been published by the Department of Health to meet the requirements for the different age groups and sexes in the Community (Department of Health, 1991). The RNI is defined as ‘an amount of the nutrient that is enough, or more than enough, for about 97 per cent of people in a group’. In addition Safe Intakes (SI) have been established for another four minerals. The SI is ‘a term used to indicate intake or range of intakes of a nutrient for which there is not enough information to estimate RNI . . . it is an amount that is enough for almost everyone but not so large as to cause undesirable effects’. The RNI for minerals for adult men and women are given in Table 4.2. 4.4 Dietary sources, supplementation and fortification Because our food is almost entirely made up of components that were once parts of living organisms and since there is a broad similarity between the nutritional requirements and cellular biochemistry of most forms of animal and plant life, it is to be expected that our needs for the mineral nutrients will be met by a conventional mixed diet (Coultate, 1985). It is usually only in exceptional situations, where, for example, there is a reliance on locally produced food in an area where 100 The nutrition handbook for food processors Table 4.2 Reference nutrient intakes and safe intakes for minerals Mineral male (19–50 years) female (19–50 years) Calcium (RNI) mg/day 700 700 Phosphorus (RNI) mg/day 550 550 Magnesium (RNI) mg/day 300 270 Sodium (RNI) mg/day 1600 1600 Potassium (RNI) mg/day 3500 3500 Chloride (RNI) mg/day 2500 2500 Iron (RNI) mg/day 8.7 14.8+ Zinc (RNI) mg/day 9.5 7.0 Copper (RNI) mg/day 1.2 1.2 Selenium (RNI) mg/day 75 60 Iodine (RNI) mg/day 140 140 Manganese (SI) mg/day above 1.4 above 1.4 Molybdenum (SI) mg/day 50–400 50–400 Chromium (SI) mg/day above 25 above 25 Fluoride (SI) mg/kg body weight/day 0.5 0.5 + insufficient for women with high menstrual losses where the most practical way of meeting iron requirements is to take iron supplements. adapted from Department of Health (1991) Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. HMSO: London
Minerals 101 Table 4.3 Good food sources of minerals Mineral cereal vegetable dairy meat Fish other *fortified * green iodised salt Brewer's yeast the soil is deficient in a particular mineral, or where the diet is deliberately restricted to a limited number of food types, that problems of mineral deficien cles occur Some food sources are better than others as sources of minerals. Plant foods are generally poor in iron and zinc, with the exception of certain dark greer vegetables such as spinach. Dairy products are generally an excellent source of calcium. Red meat and offal, such as liver, are the best dietary sources of easily absorbed iron. Many of the trace elements are found in relatively high concen- trations in fish and other seafoods Table 4.3 lists some of the best food sources of a number of the essential minerals. As is indicated in the table. there are some unusually good sources of a number of these minerals. Milk, for example, is often an excellent source of iodine because of the presence of residual iodine containing compounds used to sterilise dairy equipment. Tea is a major source of manganese in the Uk diet. An important source of chromium in the diet of some people is canned food which picks up the metal that is one of the ingredi- ents of the alloy used to produce 'tincans(Reilly, 2002) For many people supplements are an important source of minerals. It has been estimated that as many as 40% of the Us population consume them, and up to 60%o in the Uk, either as over-the-counter self-selected products or prescribed by a physician or other health advisor(Balluz et al, 2000) Mineral supplements are available in a number of chemical forms, either as inorganic compounds, such as ferrous sulphate and calcium carbonate, or as organic preparations such as selenium yeast and zinc gluconate. The products vary in the amounts of the different elements they contain, in their absorbability and in other qualities and while undoubtedly their use can make a definite con- tribution in some cases to nutritional health, there can also be problems such as over-dosing and interactions with other components of the diet(huffman et al 1999)
the soil is deficient in a particular mineral, or where the diet is deliberately restricted to a limited number of food types, that problems of mineral deficiencies occur. Some food sources are better than others as sources of minerals. Plant foods are generally poor in iron and zinc, with the exception of certain dark green vegetables such as spinach. Dairy products are generally an excellent source of calcium. Red meat and offal, such as liver, are the best dietary sources of easily absorbed iron. Many of the trace elements are found in relatively high concentrations in fish and other seafoods. Table 4.3 lists some of the best food sources of a number of the essential minerals. As is indicated in the table, there are some unusually good sources of a number of these minerals. Milk, for example, is often an excellent source of iodine because of the presence of residual iodinecontaining compounds used to sterilise dairy equipment. Tea is a major source of manganese in the UK diet. An important source of chromium in the diet of some people is canned food which picks up the metal that is one of the ingredients of the alloy used to produce ‘tin’cans (Reilly, 2002). For many people supplements are an important source of minerals. It has been estimated that as many as 40% of the US population consume them, and up to 60% in the UK, either as ‘over-the-counter’ self-selected products or prescribed by a physician or other health advisor (Balluz et al, 2000). Mineral supplements are available in a number of chemical forms, either as inorganic compounds, such as ferrous sulphate and calcium carbonate, or as organic preparations such as selenium yeast and zinc gluconate. The products vary in the amounts of the different elements they contain, in their absorbability and in other qualities and while undoubtedly their use can make a definite contribution in some cases to nutritional health, there can also be problems such as over-dosing and interactions with other components of the diet (Huffman et al, 1999). Minerals 101 Table 4.3 Good food sources of minerals Food Mineral cereal vegetable dairy meat Fish other Ca *green * * nuts Mg * nuts Fe *fortified *green * Zn * * * Cu * * Se * * * nuts I * * iodised salt Mn * * * tea Mo * Cr * * * Brewer’s yeast