Author
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Reeves, Phillip |
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Submitted to: Proceedings Sunflower Research Workshop
Publication Type: Proceedings Publication Acceptance Date: 1/18/2000 Publication Date: 2/29/2000 Citation: Reeves, P.G. 2000. Mineral nutrient status affects cadmium bioavailability from sunflower kernels. Proceedings of the 22nd Sunflower Research Workshop, January 18-19, 2000. p.28-37. Interpretive Summary: Cadmium is a trace element found in small amounts in most foods. It is thought of as a toxin and not as a nutrient. If we eat too much cadmium over a long period of time, we might develop kidney problems. Most soils naturally contain a small amount of cadmium, and some plants grown in these soils tend to take up the cadmium and deposit it in their seeds. The sunflower is one of the plants that will do this. Regulatory agencies sometimes place restrictions on the amount of cadmium in the kernels. These restrictions are based primarily on the amount of cadmium in the kernels, and not on whether the cadmium can be absorbed from the kernels after they are eaten. Other natural factors in food, including iron, calcium, and zinc, may inhibit the absorption of cadmium. What we need to know is what effects these nutrients have on the absorption of sunflower kernel cadmium into the body. To determine this, we fed female rats 20% sunflower kernels in their diets, which also contained a low and a normal amount of each of calcium, iron, and zinc. After five weeks, we measured the amount of cadmium absorbed from the sunflower kernels. The rats fed low dietary iron or calcium absorbed more cadmium than those that were fed normal amounts of these minerals. Rats fed low zinc diets were not different from those fed normal zinc. The amount of cadmium in the body organs of the rat was larger when they were fed diets with low iron and calcium than when fed diet with normal amounts of these minerals. This work strongly suggests that the mineral composition of the diet can have a great effect on cadmium absorption, and that diet composition should be considered by regulatory agencies when determining the amount of cadmium to be allowed in food. Technical Abstract: The intake of food cadmium (Cd) in ug/day over time can increase the body burden of this element. Groups of humans who consume subsistence rice- based diets low in calcium (Ca), iron (Fe) and zinc (Zn) are more susceptible to Cd poisoning than those who consume more nutritious diets. The present study determined the effects of marginal deficiencies of these essential elements on the absorption and organ retention of Cd from a natural food that contains Cd, sunflower kernels (SFK). Weanling female rats were fed diets containing 20% SFK in a 2x2x2 factorial design with marginal and adequate amounts of Ca, Zn, and Fe. Marginal Zn (11 mg/kg) and Fe (13 mg/kg), and Cd (0.18 mg/kg) were derived solely from 20% SFK. These amounts of Fe and Zn represented 40 and 90% of the NRC requirement for the rat, respectively. The marginal Ca concentration (2.5 g/kg) was one-half the NRC requirement. After 5 wk on experiment, rats were fed 1 g of their respective diets containing SFK extrinsically labeled with 37 kBq 109**Cd, and absorption was determined by whole body counting techniques. Rats were then killed and organs collected for 109**Cd assay. Feeding 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. In contrast, the naturally occurring Zn in SFK that provided 90% of the rat's requirement was enough to deter excessive absorption of Cd. Organ content of 109**Cd and Cd followed the same general pattern as whole body absorption. These data show that marginal nutritional deficiencies of Ca and Fe can readily enhance the body burden of Cd that comes from the diet. Also, some natural competing elements for Cd contained in food, such as Zn,can by themselves minimize Cd absorption. |
