Author
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Reeves, Phillip |
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Submitted to: Cadmium Workshop Proceedings
Publication Type: Proceedings Publication Acceptance Date: 9/13/2000 Publication Date: 7/1/2001 Citation: Reeves, P.G. 2000. Mineral nutrient status and the bioavailability of cadmium from natural food sources. In: Syers, J.K, Gochfeld, M., editors. Environmental Cadmium in the Food Chain: Sources, Pathways, and Risks. Proceedings of the SCOPE (Scientific Committee on Problems of the Environment) Workshop, Belgian Academy of Sciences, Brussels, Belgium, September 13-16, 2000. Interpretive Summary: Cadmium (Cd) is a trace element found in small amounts in most foods, and is most often thought of as a toxin. If we eat too much Cd, we might develop problems with kidney function. The growth media such as soil and water may contain excess Cd, and some plants, such as sunflowers and rice, tend to take up the Cd and deposit it in their seeds. As a result, this Cd might be absorbed into the body and cause harmful effects. There are factors in food, such as iron, calcium, and zinc, that tend to inhibit the absorption of Cd. Fortunately, sunflower kernels (SFK) also take up zinc that might help counter Cd absorption, but rice does not. We compared the effects of these other nutrients on the absorption of Cd from SFK and rice. We fed female rats diets containing 20% SFK or 40% cooked, dried rice that contained Cd. The diets also contained a low and a normal amount of each of calcium, iron, and zinc. After five weeks, we measured the amount of Cd absorbed from the SFK and rice. The rats fed rice absorbed more Cd than those fed SFK. Those fed low dietary iron or calcium absorbed much more Cd than those fed normal amounts of these minerals in their diets. Rats fed SFK with low zinc were not different from those fed normal zinc; however, those fed rice with low zinc had higher Cd absorption. The amounts of Cd found in the liver and kidney were larger when the rats ate diets with low iron and calcium than when they ate diets with normal amounts of these minerals. The results of this work strongly suggest that the ability of animals, and perhaps humans, to absorb Cd depends greatly upon the food source of Cd and on the mineral composition of the food, and not solely on the concentration of Cd in that food. Technical Abstract: The intake of small amounts of food cadmium (Cd) over time can increase the body burden of this potentially toxic element. The efficiency of Cd absorption might depend on the food source and its mineral composition. The present study determined the effects of different concentrations of essential dietary minerals on the absorption and organ retention of Cd from some natural foods that contain Cd. Weanling female rats were fed diets containing 20% sunflower kernels (SFK) or 40% cooked, dried rice in a 2x2x2 factorial design with marginal and adequate amounts of Ca, Zn, and Fe. After 5 wk on experiment, rats were fed 1.0 g of their respective diets containing SFK or rice extrinsically labeled with 37 kBq 109**Cd, and absorption was determined by whole body counting techniques. No effect of treatment on weight gain was observed; however, rats fed the rice diet absorbed more Cd than those fed SFK. Feeding SFK with marginal Ca elevated Cd absorption by 50% (p<0.05) over those fed adequate Ca. Feeding marginal Fe elevated Cd absorption >2.5-fold (p<0.001) over those fed adequate Fe, and a deficiency of Fe and Ca elevated absorption even more. Feeding rice with marginal Ca elevated Cd absorption 2-fold. Little effect was seen with marginal Fe unless Ca was also marginal, then Cd absorption was elevated. The naturally occurring Zn in SFK providing 90% of the rat's requirement was enough to deter excessive absorption of Cd. However, Zn in rice is naturally low, thus, Cd absorption was elevated in rats fed this diet. Data shows marginal nutritional deficiencies of Ca and Fe, and sometimes Zn, can enhance the body burden of Cd that comes from the diet. Some elements in foods that compete for Cd in foods, such as Zn, can independently affect the rate of Cd absorption. |
