Organ meats, especially liver, are the richest copper sources, followed by seafood, nuts, seeds and potatoes. Milk contains only a low level of copper. The observed copper intake in humans is relatively low, 0.9-1.2 mg/day. Zinc, vitamin C, iron, calcium, protein and dietary fibre as well as a high fructose intake are known to reduce copper absorption and may thus affect copper status (4). The recommended/safe daily intake for copper is given in Table 7 (131).
Chromium acts principally in conjunction (as cofactor) with insulin. It is required for a normal insulin activity and consequently a normal regulation of the blood glucose level. Accordingly, experimental chromium deficiency
Table 7 Recommended/safe daily intakes for trace minerals
NRC = National Research Council, Recommended Dietary Allowances, 1989 (USA). DGE = Deutsche Gesellschaft fur Ernahrung, Empfehlungen fur die Nahrstoffzufuhr, 1991. f = female, m = male.
results in decreased insulin sensitivity, impaired blood glucose regulation and possibly diabetes. Because of its role in insulin-CHO-energy metabolism, chromium is thought to be of particular importance for people involved in heavy physical work and consuming CHO rich diets. Blood chromium does not appear to be a good marker of chromium status. Urinary chromium losses are a cumulative total of small transitory changes in the blood and appear to be a better indicator of changes in chromium metabolism (3, 5, 97, 131).
Different types of stress, including exercise, infection and physical trauma, are known to exacerbate the signs of marginal chromium deficiency. In the case of exercise this occurs most probably because exercise enhances chromium losses with urine. Additionally, CHO rich diets, especially high glycaemic CHO sources, such as sugars, are known to increase chromium losses with urine. This is most likely an effect of these CHOs on quantitative insulin secretion and subsequent degradation (5). On the other hand it has been shown that CHO loading reduces the rate of trace elements loss, notably chromium and zinc (405). The explanation for this observation is that the level of actual exercise stress influences urinary excretion of these trace elements. In this study, the CHO loading regimen reduced the level of exercise stress as measured by changes in serum cortisol. Losses of potassium, magnesium and calcium were not influenced. These opposite findings on the effects of CHO on chromium levels in the body make it difficult to draw any conclusion. The loss of chromium in sweat has not been quantified using acceptable collection and analytical techniques.
Animal studies have indicated that a poor chromium status is associated with reduced glycogen stores in liver and muscle and that chromium supplementation enhances glycogen storage in this situation. Since endurance performance as well as protein oxidation are influenced by the availability of CHO, it is suggested that sufficient dietary chromium optimizes endurance performance capacity. It has been suggested in various papers that the potentiating action of chromium on insulin is responsible for enhanced incorporation of amino acids in muscle tissue and that this will lead to an increased lean body mass and decreased fat mass (3-5, 35, 37, 96, 103).
Beneficial effects are claimed for chromium picolinate (Cr-pic), which is a fat-soluble compound that easily penetrates cells and enhances insulin internalization (396, 397). Enhanced insulin activity has been observed in adipose tissue samples (395,396) and glucose uptake was enhanced in yeast cells, due to the presence of Cr-pic. Based on such observations, it has been suggested that Cr-pic maximizes insulin action in skeletal muscle leading to increased muscle mass, reduced fat mass and improved glucose utilization. However, data obtained to support these actions in humans are all of an indirect nature (397, 398) and are criticized for the small number of subjects and experimental design (403). In one study (61) in strength athletes, chromium supplementation in the form of chromium picolinate increased lean body mass and decreased fat mass, as indicated by anthropometric measures only. However, care should be taken with the interpretation of these results, as the chromium status in the test subjects was not controlled and the anthropometric measures used are not a very precise way of determining true muscle mass. Moreover, the patent owners who will benefit from any positive outcome performed the study. In a well controlled study on the effects of Cr-pic supplementation on body composition (400) no effects were observed. Recently the effect of chromium supplementation was reviewed in various papers (400-404). The following conclusions were drawn:
Independent direct data that show increased protein synthesis as well as insulinic action in human subjects are required to substantiate any beneficial claim made in the current market. Today such data do not exist.
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