|Nielsen, Forrest - Frosty|
Submitted to: European Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2003
Publication Date: 5/1/2004
Citation: Nielsen, F.H., Milne, D.B. 2004. A moderately high intake compared to a low intake of zinc depresses magnesium balance and alters indices of bone turnover in postmenopausal women. European Journal of Clinical Nutrition. 58:703-710. Interpretive Summary: Both copper and zinc have biochemical roles important for normal bone formation and turnover. Thus, deficiency of either element can have adverse effects on bone maintenance. Although zinc supplementation has been shown to be beneficial to bone growth, development and maintenance, if fed in high amounts, zinc can adversely affect calcium metabolism and bone health. When a moderately high intake of zinc has detrimental effects, it is often attributed to the result of high zinc causing a copper deficiency or altered utilization. Thus, an experiment was performed on postmenopausal women to ascertain whether moderately deficient or high dietary zinc adversely affects mineral (calcium and magnesium) metabolism important for maintaining healthy bone and induces changes in indices indicating undesirable changes in bone, and if effects were found, whether they were more marked when dietary copper was relatively low. Findings were obtained that indicated a moderately high intake of zinc does not induce changes in copper metabolism that result in a detrimental effect on bone mineral metabolism. Instead, the findings indicate that low dietary zinc might be a nutritional stressor of bone maintenance in postmenopausal women. Moreover, instead of affecting copper, a moderately high intake of zinc had an apparent unfavorable effect on magnesium balance. Because magnesium is involved in bone formation and turnover, high intakes of zinc possibly could adversely affect bone health by altering magnesium metabolism. However, further study is needed to ascertain whether high dietary zinc would be of concern for individuals consuming a relatively low amount of magnesium.
Technical Abstract: An experiment was performed to determine whether moderately high or low intakes of zinc adversely affect the copper status of postmenopausal women to result in unfavorable changes in calcium and magnesium metabolism and other indicators of bone turnover. Twenty-eight postmenopausal women were recruited and 21 completed the study of the following design while living on a metabolic unit under 24-hour supervision. After a 10-day equilibration period in which the diet provided 2 mg of copper and 9 mg of zinc per 2000 kcal, the subjects were randomly divided into two groups with one fed the basal diet supplemented to provide 1 mg of copper per 2000 kcal, and the other group fed the same diet supplemented to provide 3 mg of copper per 2000 kcal. After equilibration, both groups were fed the basal diet with no zinc supplemented (provided 3 mg zinc per 2000 kcal) for 90 days; this was followed by another 10-day equilibration period before the basal diet was supplemented with zinc to provide 53 mg of zinc per 2000 kcal for 90 days. The moderately high intake compared to the low intake of zinc increased the excretion of magnesium in the feces and urine, which resulted in a decreased magnesium balance. In the women fed the low dietary copper, plasma osteocalcin was higher during the low zinc than high zinc dietary period. The urinary excretion of N-telopeptides was increased and the serum calcitonin concentration was decreased by high dietary zinc regardless of dietary copper. The findings show that low dietary zinc induced undesirable changes in bone status indicators, and that a moderately high intake of zinc (53 mg per day) did not induce changes in copper metabolism that resulted in unfavorable changes in bone or mineral metabolism. However, because a moderately high intake of zinc decreased magnesium balance, further study of the possibility that a high intake of zinc is a health concern for individuals consuming less than the recommended amounts of magnesium is warranted.