《食品加工营养手册》参考资料（英文版）4 Minerals

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

资源类别：文库，文档格式：PDF，文档页数：20，文件大小：156.37KB，团购合买

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

102 The nutrition handbook for food processors The addition of minerals and other nutrients to foods to increase their nutri- tional value is widely practised. In the 1920s iodised salt was introduced in some countries to help combat endemic goitre. iodised salt, as well as other iodised foods such as bread and monosodium glutamate, are today widely used in part of the world where iodine deficiency diseases (IDD) are still endemic, such as India, and China, Papua New Guinea, Central Africa and the Andean region of South americ Legislation was introduced in several countries during World War II which required the addition of iron and calcium, as well as of certain water-soluble vitamins, to bread and flour in order to combat nutritional deficiencies caused by food restrictions. The success of these measures in improving health led to the extension of the legislation into peacetime. Some countries, such as the UK, still require that bread and flour be fortified with calcium and iron(Statutory Instrument, 1984) Bread and four are the only foodstuffs required by law to be fortified with minerals in the UK. There is, in addition, legal provision for the voluntary addi tion by food processors of other minerals to other foodstuffs, with the exception of alcoholic drinks. This has given manufacturers the opportunity to produce a variety of foods enriched with other minerals. Most ready-to-eat(RTE) breakfast cereals are enriched with iron and zinc. some varieties will also contain added iodine and other minerals. These are normally added at levels which are well below those which might cause toxic effects(Brady, 1996). Fortified RTE cereals have been shown to make a significant contribution towards meeting the nutri tional requirements of consumers for iron, as well as for copper, manganese and zinc (Booth et al, 1996). Currently a considerable amount of research is being carried out on methods, such as fortification of a variety of commonly used foods with minerals and other nutrients, as a way of improving nutritional status countries where deficiency problems regularly occur( Gibson and Ferguson 1998) In recent years there has been a growth in the production of foods, which have been deliberately selected or formulated to provide, according to their promotors, specific physiologic, health promoting and even disease-preventing benefits They have been given a variety of names such as ' designer food,'nutraceuti- cals, 'functional foodsand, officially in Japan, ' foods for specific health use FOSHU). Several of these products contain minerals such as selenium(Reilly, 1998) 4.5 Calcium Without an adequate supply of the macromineral calcium in the diet calcification of the skeleton will be adversely affected. During early growth and development the supply of calcium for this purpose is particularly critical and for this re the amount required by a child is proportionally greater than for an adult ( Nutrition Foundation, 1989)

The addition of minerals and other nutrients to foods to increase their nutritional value is widely practised. In the 1920s iodised salt was introduced in some countries to help combat endemic goitre. Iodised salt, as well as other iodised foods such as bread and monosodium glutamate, are today widely used in parts of the world where iodine deficiency diseases (IDD) are still endemic, such as India, and China, Papua New Guinea, Central Africa and the Andean region of South America. Legislation was introduced in several countries during World War II which required the addition of iron and calcium, as well as of certain water-soluble vitamins, to bread and flour in order to combat nutritional deficiencies caused by food restrictions. The success of these measures in improving health led to the extension of the legislation into peacetime. Some countries, such as the UK, still require that bread and flour be fortified with calcium and iron (Statutory Instrument, 1984). Bread and flour are the only foodstuffs required by law to be fortified with minerals in the UK. There is, in addition, legal provision for the voluntary addition by food processors of other minerals to other foodstuffs, with the exception of alcoholic drinks. This has given manufacturers the opportunity to produce a variety of foods enriched with other minerals. Most ready-to-eat (RTE) breakfast cereals are enriched with iron and zinc. Some varieties will also contain added iodine and other minerals. These are normally added at levels which are well below those which might cause toxic effects (Brady, 1996). Fortified RTE cereals have been shown to make a significant contribution towards meeting the nutritional requirements of consumers for iron, as well as for copper, manganese and zinc (Booth et al, 1996). Currently a considerable amount of research is being carried out on methods, such as fortification of a variety of commonly used foods with minerals and other nutrients, as a way of improving nutritional status in countries where deficiency problems regularly occur (Gibson and Ferguson, 1998). In recent years there has been a growth in the production of foods, which have been deliberately selected or formulated to provide, according to their promotors, specific physiologic, health promoting and even disease-preventing benefits. They have been given a variety of names such as ‘designer food’, ‘nutraceuticals’, ‘functional foods’ and, officially in Japan, ‘foods for specific health use’ (FOSHU). Several of these products contain minerals such as selenium (Reilly, 1998). 4.5 Calcium Without an adequate supply of the macromineral calcium in the diet calcification of the skeleton will be adversely affected. During early growth and development the supply of calcium for this purpose is particularly critical and for this reason the amount required by a child is proportionally greater than for an adult (British Nutrition Foundation, 1989). 102 The nutrition handbook for food processors

Minerals 103 4.5.1 Calcium absorption Uptake of calcium from food in the gut is not very efficient. Only about 30% is sorbed, with 70% lost in faeces. Absorption is a complex process, which is under the control of the cholecalciferol(vitamin D)-parathyroid hormone system Calcium is transported across the intestinal mucosa bound to a special carrier protein. Synthesis of this protein is stimulated by an activated form of cholecal- ciferol, 1, 25-dihydroxycholecalciferol (1, 25-DHCC) If vitamin D levels are low, calcium absorption will be restricted and a deficiency will occur. To be absorbed. calcium must be in the soluble ionic form. Several food components can prevent this happening. These include phytic acid (inositol hexaphosphate) in cereals, and oxalate in certain dark green vegetables, such as spinach, and in rhubarb. Uronic acid in dietary fibre can have a similar effect, as can free fatty acids and certain other dietary factors, including sodium chloride and a high protein intake 4.5.2 Functions of calcium in the body Over 99%o of body calcium is in the skeleton, where it both provides structural support and serves as a reservoir for maintaining plasma levels. Calcium in plasma plays a number of roles, for example in muscle contraction, neurous- cular function and blood coagulation. To maintain these roles, calcium levels in the plasma must be very stable. If for any reason they are altered, they are imme- diately restored to normal levels by an increased secretion of parathyroid hormone and the formation of 1, 25-DHCC. In children this increase in plasma calcium means that less of the mineral goes into bones, while in adults calcium is withdrawn from the skeleton. In either case there can be significant implica tions for bone structure 4.5.3 Osteoporosis Osteoporosis is a condition which is characterised by loss of bone tissue from the skeleton and deterioration of bone structure with enhanced bone fragility and increased risk of fracture. It is relatively common in the elderly, especially females, but may also occur in the young. In the UK one in three women and one in twelve men over the age of 50 years can expect to have an osteoporotic frac ture during the remainder of their lives(Prentice, 2001 ). The causes of osteoporosis, in spite of extensive research, remain elusive. The higher rate in women seems to be associated with a number of factors: the lower skeletal mass in women compared to men, a greater rate of calcium loss and a fall in oestrogen production with age. Lifetime history is also important. Higher intakes of calcium, especially in adolescence and early adulthood, ensure greater bone density. In addition, physical exercise can help increase calcium deposition, while high consumption of alcohol, coffee, meat, salt and cola beverages may contribute to decreased bone density(Sakamoto et al, 2001) Although there is considerable debate about the effectiveness of calcium sup

4.5.1 Calcium absorption Uptake of calcium from food in the gut is not very efficient. Only about 30% is absorbed, with 70% lost in faeces. Absorption is a complex process, which is under the control of the cholecalciferol (vitamin D)-parathyroid hormone system. Calcium is transported across the intestinal mucosa bound to a special carrier protein. Synthesis of this protein is stimulated by an activated form of cholecalciferol, 1,25-dihydroxycholecalciferol (1,25-DHCC). If vitamin D levels are low, calcium absorption will be restricted and a deficiency will occur. To be absorbed, calcium must be in the soluble ionic form. Several food components can prevent this happening. These include phytic acid (inositol hexaphosphate) in cereals, and oxalate in certain dark green vegetables, such as spinach, and in rhubarb. Uronic acid in dietary fibre can have a similar effect, as can free fatty acids and certain other dietary factors, including sodium chloride and a high protein intake. 4.5.2 Functions of calcium in the body Over 99% of body calcium is in the skeleton, where it both provides structural support and serves as a reservoir for maintaining plasma levels. Calcium in plasma plays a number of roles, for example in muscle contraction, neuromuscular function and blood coagulation. To maintain these roles, calcium levels in the plasma must be very stable. If for any reason they are altered, they are immediately restored to normal levels by an increased secretion of parathyroid hormone and the formation of 1,25-DHCC. In children this increase in plasma calcium means that less of the mineral goes into bones, while in adults calcium is withdrawn from the skeleton. In either case there can be significant implications for bone structure. 4.5.3 Osteoporosis Osteoporosis is a condition which is characterised by loss of bone tissue from the skeleton and deterioration of bone structure with enhanced bone fragility and increased risk of fracture. It is relatively common in the elderly, especially females, but may also occur in the young. In the UK one in three women and one in twelve men over the age of 50 years can expect to have an osteoporotic fracture during the remainder of their lives (Prentice, 2001). The causes of osteoporosis, in spite of extensive research, remain elusive. The higher rate in women seems to be associated with a number of factors: the lower skeletal mass in women compared to men, a greater rate of calcium loss and a fall in oestrogen production with age. Lifetime history is also important. Higher intakes of calcium, especially in adolescence and early adulthood, ensure greater bone density. In addition, physical exercise can help increase calcium deposition, while high consumption of alcohol, coffee, meat, salt and cola beverages may contribute to decreased bone density (Sakamoto et al, 2001). Although there is considerable debate about the effectiveness of calcium supMinerals 103

104 The nutrition handbook for food processors for calcium deficiency in i,.porosis, the weight of evidence points towards a role plements in preventing oste ts genesis and for calcium therapy in its prevention and management, at least in postmenopausal women(Heaney, 2001). Increases in bone mineral density(BMD)have been observed following calcium supplemen tation in young, as well as in elderly subjects. However, although dietary calcium does play a major role in optimisation of bone mineralisation it is by no means the only factor involved(Prentice, 1997) 4.5.4 Recommended intakes of calcium There is at present no international consensus regarding calcium requirements and levels in the diet necessary to meet optimum requirements Recommended intakes differ widely between countries, partly because different methods have been used to arrive at the recommendations. While some authorities have focused on meeting nutritional requirements, others have aimed at optimising bone density (Wynne, 1998). There is also the fact that actual intakes of calcium vary widely world-wide, without, in many cases, an apparent effect on bone develop- ment. In parts of Africa and Asia intake of dietary calcium is as low as 300- 400 mg/day, while in Northern Europe it can be 1500mg/day or more In the UK the Panel for Dietary Reference Values of COMA(the Committee on Medical Aspects of Food Policy) of the Department of Health, while noting the difficulty of assessing the adequacy of the dietary supply of calcium, has established RNIs for calcium for different groups in the population(Department of Health, 1991). Since the panels experts found that no single approach to the estimation of these values was considered to be satisfactory, these intakes are not onsidered to represent true basal dietary requirements, but rather to describe the apparent calcium requirements of healthy people in the UK under prevailing leary The UK RNi for adults age ged 19-50 years is 700 mg/day, with an additional 550mg/day for lactating women. In the US an intake of 1000 mg/day is recom- ge group, with no additional Institute of Medicine, Food and Nutrition Board, 1998). In contrast, WHO/FAO in 1974 proposed 400-500 mg/day for this group, with additional intakes for pregnant and lactating women. 4.5.5 Dietary sources of calcium Milk and dairy products are the major sources of calcium in many diets In coun ries such as the UK where addition of calcium to flour is required by law, bread and other cereal products also make an important contribution to intake Sardines and other small fish, which are eaten whole, are also good sources. In countries where dairy products are not used in quantity and where fortification of flour is not required, requirements may be met by green leafy vegetables, roots, nuts and pulses. Where domestic water is hard, with a high calcium content, it can make a significant contribution to intake

plements in preventing osteoporosis, the weight of evidence points towards a role for calcium deficiency in its genesis and for calcium therapy in its prevention and management, at least in postmenopausal women (Heaney, 2001). Increases in bone mineral density (BMD) have been observed following calcium supplementation in young, as well as in elderly subjects. However, although dietary calcium does play a major role in optimisation of bone mineralisation it is by no means the only factor involved (Prentice, 1997). 4.5.4 Recommended intakes of calcium There is at present no international consensus regarding calcium requirements and levels in the diet necessary to meet optimum requirements. Recommended intakes differ widely between countries, partly because different methods have been used to arrive at the recommendations. While some authorities have focused on meeting nutritional requirements, others have aimed at optimising bone density (Wynne, 1998). There is also the fact that actual intakes of calcium vary widely world-wide, without, in many cases, an apparent effect on bone development. In parts of Africa and Asia intake of dietary calcium is as low as 300– 400 mg/day, while in Northern Europe it can be 1500 mg/day or more. In the UK the Panel for Dietary Reference Values of COMA (the Committee on Medical Aspects of Food Policy) of the Department of Health, while noting the difficulty of assessing the adequacy of the dietary supply of calcium, has established RNIs for calcium for different groups in the population (Department of Health, 1991). Since the panel’s experts found that no single approach to the estimation of these values was considered to be satisfactory, these intakes are not considered to represent true basal dietary requirements, but rather to describe the apparent calcium requirements of healthy people in the UK under prevailing dietary circumstances. The UK RNI for adults aged 19–50 years is 700 mg/day, with an additional 550 mg/day for lactating women. In the US an intake of 1000 mg/day is recommended for the same age group, with no additional allowance for lactation (Institute of Medicine, Food and Nutrition Board, 1998). In contrast, WHO/FAO in 1974 proposed 400–500 mg/day for this group, with additional intakes for pregnant and lactating women. 4.5.5 Dietary sources of calcium Milk and dairy products are the major sources of calcium in many diets. In countries such as the UK where addition of calcium to flour is required by law, bread and other cereal products also make an important contribution to intake. Sardines and other small fish, which are eaten whole, are also good sources. In countries where dairy products are not used in quantity and where fortification of flour is not required, requirements may be met by green leafy vegetables, roots, nuts and pulses. Where domestic water is ‘hard’, with a high calcium content, it can make a significant contribution to intake. 104 The nutrition handbook for food processors

Minerals 105 4.5.6 High intakes of calcium The consumption of calcium supplements is widely practised, especially by the elderly as a precaution against the development of osteoporosis. Although there is little evidence that a high intake of calcium resulting from supplement con- sumption causes adverse health effects, in the US an Upper Intake Level (UL) has been set for the mineral at 2.5g/day. A Safe Intake(SD) level has not been set in the UK on the grounds, according to the Department of Health, that calcium metabolism is under such close homeostatic control that an excessive accumula- tion in the blood(hypercalcaemia) or in tissues(calcification) from overcon sumption is virtually unknown(Department of Health, 1991) 4.6 Iron In spite of the fact that iron is the second most abundant metal in the earths c iron insufficiency is probably the most common nutritional deficiency in l, world. Even among the inhabitants of well-fed developed countries it continues to be common, especially in women(Looker et al, 1997) 4.6.1 Iron absorption The uptake of iron is a complex and highly regulated operation. Once the element is absorbed from the intestine into the blood, only small amounts are lost from the body, except when bleeding occurs. There is no physiological mechanism for secretion of iron, so iron homeostasis depends on its absorption. Thus the healthy individual with a good store of iron is able to maintain a balance between the small normal losses and the amounts of the element absorbed from food Normally only a very small amount of iron, about 1 mg/day, needs to be absorbed. The metal first enters the intestinal mucosal cells where it is bound into ferritin an iron-storage protein. This is a large molecule from which the iron can be readily mobilised when required. Some of the incoming iron may be transferred directly by a transport protein, transferrin, to bone marrow and other tissues to be used in the synthesis of haemoglobin and myoglobin. Iron absorption is apparently regulated by the existing iron status of the body this is low, the absorption mechanism can be stimulated to increased activity. When iron stores are high, absorption is slowed down. There is evidence that other mineral elements, such as zinc, can compete with iron for the active absorp- tion pathway. Several other dietary factors can affect absorption, including phytate and fibre, which inhibit absorption, and ascorbic acid and protein, which ncrease uptake. The pH of the gut also has an effect, with food iron mainly in the more readily absorbed ferrous state under acid conditions 4. 6.2 Functions of iron Iron is an essential nutrient for all living organisms, with the exception of certain bacteria. It has two major roles in human physiology. As a component of haemo-

4.5.6 High intakes of calcium The consumption of calcium supplements is widely practised, especially by the elderly as a precaution against the development of osteoporosis. Although there is little evidence that a high intake of calcium resulting from supplement consumption causes adverse health effects, in the US an Upper Intake Level (UL) has been set for the mineral at 2.5 g/day. A Safe Intake (SI) level has not been set in the UK on the grounds, according to the Department of Health, that calcium metabolism is under such close homeostatic control that an excessive accumulation in the blood (hypercalcaemia) or in tissues (calcification) from overconsumption is virtually unknown (Department of Health, 1991). 4.6 Iron In spite of the fact that iron is the second most abundant metal in the earth’s crust, iron insufficiency is probably the most common nutritional deficiency in the world. Even among the inhabitants of well-fed developed countries it continues to be common, especially in women (Looker et al, 1997). 4.6.1 Iron absorption The uptake of iron is a complex and highly regulated operation. Once the element is absorbed from the intestine into the blood, only small amounts are lost from the body, except when bleeding occurs. There is no physiological mechanism for secretion of iron, so iron homeostasis depends on its absorption. Thus the healthy individual with a good store of iron is able to maintain a balance between the small normal losses and the amounts of the element absorbed from food. Normally only a very small amount of iron, about 1 mg/day, needs to be absorbed. The metal first enters the intestinal mucosal cells where it is bound into ferritin, an iron-storage protein. This is a large molecule from which the iron can be readily mobilised when required. Some of the incoming iron may be transferred directly by a transport protein, transferrin, to bone marrow and other tissues to be used in the synthesis of haemoglobin and myoglobin. Iron absorption is apparently regulated by the existing iron status of the body. If this is low, the absorption mechanism can be stimulated to increased activity. When iron stores are high, absorption is slowed down. There is evidence that other mineral elements, such as zinc, can compete with iron for the active absorption pathway. Several other dietary factors can affect absorption, including phytate and fibre, which inhibit absorption, and ascorbic acid and protein, which increase uptake. The pH of the gut also has an effect, with food iron mainly in the more readily absorbed ferrous state under acid conditions. 4.6.2 Functions of iron Iron is an essential nutrient for all living organisms, with the exception of certain bacteria. It has two major roles in human physiology. As a component of haemoMinerals 105

106 The nutrition handbook for food processors globin, the red pigment of blood and myoglobin in muscle, iron atoms combine reversibly with oxygen to act as its carrier from the lungs to the tissues. In a variety of enzymes, such as the cytochromes, iron atoms, present in the ferrous and ferric states, interchange with gain or loss of an electron, as part of the elec tron chain responsible for the redox reactions necessary for release of energy in cellular catabolism and the synthesis of large molecules(Brock et al, 1994) In addition to its major functions in oxygen transport and as a cofactor in many A.ymes, iron also plays an important role in the immune system. Although the chanisms involved are complex, there is good evidence that an abnormal iron nutritional status can lead to impaired immune function, with serious conse- quences for health(Walter et al, 1997) 4.6.3 Iron deficiency anaemia Iron deficiency ultimately results in failure of the body to produce new blood cells to replace those that are constantly being destroyed at the end of their normal 120-day life span. Gradually the number of blood cells falls and, with this, the amount of haemoglobin in the blood. The cells become paler in colour and smaller in size. These undersized cells are unable to carry sufficient oxygen to meet the needs of tissues, so energy release is hindered. This is what is known technically as microcytic hypochromic anaemia, or, simply, as iron deficiency anaemia(IDA) Expert Scientific Working Group, 1985). Because the fall in red blood cells occurs gradually, IDA can exist for a considerable time before it is clearly detected. By then iron stores have suffered a critical fall and the person affected shows symptoms of chronic tiredness, persistent headache, and, in many cases, a rapid heart rate on exertion. There may also be other functional consequences of iron deficiency, including a decreased work capacity, a fall in intellectual per- formance, and a reduction in immune function( Brock and mulero, 2000). There is today growing concern at the possibility that iron deficiency in infancy and childhood can have serious consequences, such as morbidity in the newborn, defects in growth and development of infants and impaired educational perfor- mance in schoolchildren(Cook, 1999) 4.6.4 Recommended intakes The UK RNI is 1.7-8. 7 mg/day for both males and females from birth to 10 years of age. This rises to 14.8 mg/day for females from 1l to 50 years, when it is reduced to 8.7 for the post-child bearing years. Women with a high menstrual loss are recommended to increase their iron intake by taking a supplement. The RNI for males from 11 to 18 years is set at 11.3 mg/day, with a drop to 8.7 mg/day for later years(Department of Health, 1991). The UK recommendations are similar to those published in the US(National Research Council, 1989), but lower than those of WHO. They are also less than recommendations in many developing countries. In Indonesia, for instance, an intake of 14-26mg/day is recommended for women of child-bearing age, with

globin, the red pigment of blood and myoglobin in muscle, iron atoms combine reversibly with oxygen to act as its carrier from the lungs to the tissues. In a variety of enzymes, such as the cytochromes, iron atoms, present in the ferrous and ferric states, interchange with gain or loss of an electron, as part of the electron chain responsible for the redox reactions necessary for release of energy in cellular catabolism and the synthesis of large molecules (Brock et al, 1994). In addition to its major functions in oxygen transport and as a cofactor in many enzymes, iron also plays an important role in the immune system. Although the mechanisms involved are complex, there is good evidence that an abnormal iron nutritional status can lead to impaired immune function, with serious consequences for health (Walter et al, 1997). 4.6.3 Iron deficiency anaemia Iron deficiency ultimately results in failure of the body to produce new blood cells to replace those that are constantly being destroyed at the end of their normal 120-day life span. Gradually the number of blood cells falls and, with this, the amount of haemoglobin in the blood. The cells become paler in colour and smaller in size. These undersized cells are unable to carry sufficient oxygen to meet the needs of tissues, so energy release is hindered. This is what is known technically as microcytic hypochromic anaemia, or, simply, as iron deficiency anaemia (IDA) (Expert Scientific Working Group, 1985). Because the fall in red blood cells occurs gradually, IDA can exist for a considerable time before it is clearly detected. By then iron stores have suffered a critical fall and the person affected shows symptoms of chronic tiredness, persistent headache, and, in many cases, a rapid heart rate on exertion. There may also be other functional consequences of iron deficiency, including a decreased work capacity, a fall in intellectual performance, and a reduction in immune function (Brock and Mulero, 2000). There is today growing concern at the possibility that iron deficiency in infancy and childhood can have serious consequences, such as morbidity in the newborn, defects in growth and development of infants and impaired educational performance in schoolchildren (Cook, 1999). 4.6.4 Recommended intakes The UK RNI is 1.7–8.7 mg/day for both males and females from birth to 10 years of age. This rises to 14.8 mg/day for females from 11 to 50 years, when it is reduced to 8.7 for the post-child bearing years. Women with a high menstrual loss are recommended to increase their iron intake by taking a supplement. The RNI for males from 11 to 18 years is set at 11.3 mg/day, with a drop to 8.7 mg/day for later years (Department of Health, 1991). The UK recommendations are similar to those published in the US (National Research Council, 1989), but lower than those of WHO. They are also less than recommendations in many developing countries. In Indonesia, for instance, an intake of 14–26 mg/day is recommended for women of child-bearing age, with 106 The nutrition handbook for food processors

点击进入文档下载页（PDF格式）

共20页，试读已结束，阅读完整版请下载