conspectus of researchon copper metabolism and requirements

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1998 KARL E. MASON The richest sources in human dietaries are liver (especially calf, lamb and beef), crustaceans and shell fish (especially oysters). Of somewhat lesser content, and roughly in descending order, are nuts and seeds, high-protein cereals, dried fruits, poultry, fish, meats, legumes, root vege tables, leafy vegetables, fresh fruits and non-leafy vegetables. One of the lowest of commonly used foods is cow's milk. The exceptionally high copper content of the Atlantic coast oyster, which may vary widely with the season and with degrees of contamination of environmental waters, is not true of the Pacific or the Australian oyster (290). Throughout the literature one repeatedly finds the statement that the average North American diet provides 3 to 5 mg of copper per day. Because of the widespread pres ence of copper in foods and in drinking wa ter, especially that obtained via copper pipes, it is difficult to devise a balanced diet composed of natural foodstuffs that contains less than 1 mg per day (50 /Â¿g/cal/day), according to Schroeder et al. (691) who give extensive data on copper in foods, beverages and water of many types. They also state that to provide such a diet the following foods must be avoided; most meats, shellfish, vegetables, phospholipids, legumes, fruits, nuts, some grains, gelatin, tea, coffee, soft drinks, beer and distilled liquors. Such a diet would be low in pro tein, monotonous and marginally deficient in several essential trace metals. In con trast, they estimate that a diet of only 1,200 calories, with 100 calories from each of the high copper foods (oysters, clams, pork, margarine, turnips, carrots, mushrooms, rhubarb, papaya, nuts, grapenuts and orange juice) would contain approximately 34 mg of copper. There have been many other published lists giving the copper content of com monly used foods. A rather extensive list of copper and other inorganic elements in foods used in hospital menus has been presented by Gormican (273). A recent and complete compilation of data pertain ing to the copper content of foods, as re corded by investigators worldwide, is that of Pennington and Galloway (595). Of the 222 references used in their literature sur vey only 104 specified the methods used, many of which represented individual modification of other methods. Methods of expressing values obtained were indeed numerous and often difficult to reduce to a common denominator. Aside from vari able contamination of water, reagents and glassware in analytical procedures, factors such as copper content of soil, water source, season, and use of fertilizers, insecticides, pesticides and fungicides raised serious questions concerning the validity of values reported for the copper content of the vast list of food items recorded. Hughes et al. (366) give analyses for copper in a great variety of commercially prepared baby foods. Highest levels were found in those containing beef liver and high protein cereals (2.64 and 1.85 mg/100 g, respectively). Next in order were other precooked cereal foods (range 0.78-0.26 mg/100 g), as compared to 0.04 to 0.30 mg/100 ml in human milk (pp. 2025-2026). Vegetables, fruits and desserts were vari ably lower. Cooked cereals, which fre quently are the first non-milk foods offered to infants, if they are of high protein quality, will provide a large part of their require ment. It was their opinion that by the time infants reach 6 months of age the variety of supplementary foods normally offered should, in most cases, meet or exceed the generally accepted requirement of 0.05 mg/kg/day. From what has been said, it is apparent that most populations appear to have an adequate dietary intake of copper, which well justifies previous opinions that a recog nizable state of copper deficiency in adult man is not likely to be recognized. But this does not imply that some diets may not be decidedly marginal, as discussed in the following section. Such matters are con stantly of concern in any review of reports on dietary intake and on balance studies which represent the basic information necessary for the determination of human copper requirements. Dietary intake of copper Before progressing to a discussion of human dietary needs of copper for adult man it may be pertinent to review what has been recorded concerning the usual Downloaded from jn.nutrition.org by guest on February 27, 2013
COPPER METABOLISM AND REQUIREMENTS OF MAN 1999 dietary intake in various countries of the world. At the beginning it should be recog nized that in the vast majority of such analyses copper has often been only one of many trace elements under investigation and often has been secondary compared to iron, zinc, and other elements. Unfortu nately, there have been almost no studies in which copper has been the only, or even the primary, focus of attention. On the basis of studies conducted in England, New Zealand and the United States, Underwood (798) estimates that most western-style mixed diets provide adults with 2 to 4 mg/day. Guthrie and Robinson (292) think that the copper status of some New Zealanders may be inadequate. In India, in adults consuming rice and wheat diets, the copper intake may be as much as 4.5 to 5.8 mg/day (154). Estimated daily intakes for adults in other countries have been reported as: 2.26 to 7.3 mg (mean 4.10) in Kiev and 11 other cities of the Ukraine (239); 1.29 to 6.39 mg for inmates of old people's homes in Switzerland (688); about 2.0 mg for New Zealanders (511); 1.5 mg for inhabi tants of an isolated Polynesian island (510); 2 to 4 mg for Japanese (543) and about 2.0 mg for Taiwanese (793). In the latter study, a control subject maintained on a low copper diet for 2 weeks, providing a daily intake of 1.34 mg, maintained a posi tive copper balance of 0.12 mg. Unfortu nately, the methods employed for analysis of copper were not stated. On the other hand, it is estimated that in 20 USDA diets examined the mean copper intake would provide 1.05 mg/day (419). Recent and well planned studies based upon analyses of copper and zinc content of duplicate samples of daily diets of 22 subjects ( 14-64 years of age ) over a 14-day period, provide valuable information (344, 860). Considering a 6-day average (after 8 days of adjustment) for each subject, the mean daily intake of copper was 1.01 mg day Â±0.4. This is considerably below estimates of 1.62 mg/day given by Hartley et al. (314), and 1.34 mg/day by Tu et al. (793), but in good agreement with the estimates of 1.05 mg by Klevay et al. (419). There has also been an increasing aware ness of an inadequacy of not only copper but also other trace elements and certain vitamins in the usual hospital diets (67, 273, 419). It is true that most patients are hospitalized over a sufficiently short period such that they can rely on liver and other tissue storage to compensate for inade quate intake. The problem of long term parenteral nutrition is a separate issue which will be discussed later (pp. 2028, 2034). However, it may be noted that a recent study of regular, vegetarian and renal diets in a hospital situation, based on diets collected over 7 consecutive days, in dicate a mean daily copper intake of 0.90, 1.10 and 0.51 mg (67), respectively. For subjects with Wilson's disease such diets would be most desirable. For others, they may be marginal or inadequate. Analyses of school lunches have given but rather fragmentary evidence of the copper content of the American diet for children and adolescents. A survey of such lunches served 6th grade children in 300 schools in 19 states of the USA (544, 545) indicates an average content of 0.34 mg/ day (range 0.06-2.19 mg). Considering one-third of the daily intake represented, the average intake would amount to about 1.0 mg/day. These values are somewhat less than those reported in metabolic studies of 7 to 9 year-old children fed diets typical of low income groups in the south eastern USA, recording mean daily intakes of 1.67 mg/day (618). On the basis of mg/ kg/food consumed, values given for insti tutionalized children in Samarkand are 0.46 to 1.62 (620), and for the same in 28 USA cities are 0.44 to 0.87 (548). Waslein (830) reports that data col lected on the copper content of the diet of 377 babies from the USA indicated a wide range of from 7 to 170 /*g/kg body weight, or 0.18 to 0.92 mg/day. Total daily intakes of copper ranged from an average of 0.16 for 1-month old infants to 0.38 mg for 6-month old infants, 50 to 607o of the in take coming from milk. Furthermore, in takes of children participating in balance studies or living in institutions in the USA or USSR had mean copper intakes of 0.9 to 2.2 mg/day, and similar studies on adults in the United Kingdom and New Zealand gave values of 1.7 and 2.4 mg/day, respectively. However, the average copper Downloaded from jn.nutrition.org by guest on February 27, 2013
Page 1 and 2: A CONSPECTUS OF RESEARCH ON COPPER
Page 3 and 4: INTRODUCTION The discovery of coppe
Page 5 and 6: COPPER METABOLISM AND REQUIREMENTS
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Page 55 and 56: Ã®1co 1stW Â»aÂ«a3 COPPER MET
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COPPER METABOLISM AND REQUIREMENTS
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