Submitted to: The American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/16/1999
Publication Date: 3/1/2000
Citation: Davis, C.D., Milne, D.B., Nielsen, F.H. 2000. Changes in dietary zinc and copper affect zinc status indicators of postmenopausal women, notably, extracellular superoxide dismutase and amyloid precursor proteins. American Journal of Clinical Nutrition. 71:781-788.
Interpretive Summary: Zinc and copper are two essential trace elements for human health. Recently, abnormalities of both zinc and copper metabolism have been implicated in the development of Alzheimer's disease. Alzheimer's disease is a disease characterized by a gradual loss of memory, reasoning and judgement that affects 1% of the population of the United States. The purpose of the current study was to use laboratory rats as a model to determine whether changes in dietary zinc and/or copper concentrations might affect the amount of a substance that accumulates in the brain of Alzheimer's disease patients. Although neither changes in dietary zinc nor changes in dietary copper affected the amount of the substance studied, this study will be useful to research scientists and medical doctors in determining the cause of Alzheimer's disease.
Technical Abstract: Background: Zinc is an essential trace element for human health and well being; however, methods currently available for the assessment of zinc status in humans are unsatisfactory. Objective: To critically evaluate the use of various indicators of zinc status in humans in a controlled metabolic-unit study. Design: Indicators of zinc status were measured in 25 healthy postmenopausal women, aged 64.9 +/- 6.7 y. After a 10 d equilibration period, volunteers consumed a diet that contained either low (1 mg/8.4 MJ, n=12 women ) or high (3 mg/8.4 MJ, n=13 women) dietary copper. They received the same amount of copper throughout the study. Both groups were fed the basal diet (3 mg zinc/8.4 MJ) with no zinc supplement for one 90- day period, and the diet supplemented with 50 mg of zinc per day for another 90-day period. Results: Zinc supplementation significantly increased (p<0.0001) extracellular but not erythrocyte superoxide dismutase activity. This increase was more apparent when subjects were fed low dietary copper. Zinc supplementation in combination with low dietary copper significantly (p<0.01) decreased amyloid precursor protein (APP) expression in platelets. Other indicators of zinc status which were significantly elevated with zinc supplementation include: plasma zinc and free thyroxine concentrations and mononuclear 5'-nucleotidase activity. Conclusions: The measurement of serum extracellular superoxide dismutase activity may be useful as a marker for the functional assessment of zinc status in humans.