Submitted to: Environmental Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2000
Publication Date: 3/1/2001
Citation: Reeves, P.G., Chaney, R.L. 2001. Mineral status of female rats affects the absorption and organ distribution of dietary cadmium derived from confectionery sunflower kernels (Helianthusannuus L.). Environmental Research 85:215-225. Interpretive Summary: Cadmium (Cd) is a trace element found in most foods, and it is most often thought of as a toxin. If we eat too much Cd, we might develop kidney dysfunction. Most soils naturally contain a small amount of Cd, and some plants, such as sunflowers, take up the Cd and deposit it in their seeds. As a result, the kernels contain more Cd than most other grains. Some regulatory agencies place restrictions on the amount of Cd allowed in the kernels, and these restrictions are based primarily on the amount of Cd in the kernels, and not on whether the Cd can be absorbed into the body from the ingested kernels. There are other factors in food, such as iron, calcium, and zinc, that might inhibit the absorption of Cd. So, what we need to know is what effects the other nutrients have on the absorption of Cd from sunflower kernels. To determine this, we fed female rats diets containing 20% sunflower kernels. 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 sunflower kernels. The rats fed low dietary iron or calcium absorbed much more Cd than those fed normal amounts of these minerals in their diets. Rats fed low zinc diets were not different from those that were fed normal zinc. Cd found in the small intestine, serum, liver, and kidney was higher when the rats ate diets with low iron and calcium than when they ate diets with normal amounts of these minerals. This research strongly suggests that regulatory agencies should not only consider the amount of Cd in food but also the amount of calcium and iron in that food when placing restrictions on the Cd content. Normal calcium and iron in the diet with which the Cd is eaten will lower the amount of Cd absorbed into the body.
Technical Abstract: Some human populations consuming subsistence rice-based diets low in calcium (Ca), iron (Fe) and zinc (Zn) are more susceptible to Cd poisoning than populations consuming 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, confectionery sunflower kernels (Helianthus annuus L.; CSFK). Weanling female rats were fed diets containing 20% CSFK 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% CSFK. These amounts of Fe and Zn represented 40 and 90% of the NRC requirement for the rat, respectively. The marginal dietary Ca concentration (2.5 g/kg) was one-half the NRC requirement. After 5 wk on experiment, rats were fed one 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 assays. 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, but not enough to elevate organ Cd. Organ content of 109^Cd and Cd followed the same general pattern as whole body absorption. The data show that marginal nutritional deficiencies of Ca and Fe readily enhance the body burden of Cd that comes from the diet. Also, some natural competing element, such as Zn, for Cd contained in foods can independently minimize Cd absorption.