Submitted to: Environmental Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 24, 2004
Publication Date: September 1, 2004
Citation: Reeves, P.G., Chaney, R.L. 2004. Marginal nutritional status of zinc, iron, and calcium increases cadmium retention in the duodenum and other organs of rats fed a rice-based diet. Environmental Research. 96:311-322. Interpretive Summary: Cadmium is a trace element found in most foods and the consumption of too much of this element might cause problems with kidney function. Primarily, restrictions on the amount of cadmium allowed in food are based on how much is there and not on whether the cadmium can be absorbed into the body from the ingested food. Work in our laboratory shows that low intakes of natural mineral nutrients such as zinc, iron, and calcium can increase the absorption of cadmium up to 10-fold. Some grains, such as polished rice do not contain high amounts of these mineral nutrients, but if grown in polluted paddies, it can have high amounts of cadmium. People who consume this rice as a staple food would absorb more cadmium unless they also consume adequate amounts of the other minerals. In earlier studies, we found that low intakes of zinc, iron, and calcium tended to delay the fecal excretion of cadmium. The current study was designed to determine the time course of cadmium accumulation and movement in the intestine and liver and kidneys. The results showed that rats consuming a marginal dietary amount of zinc, iron, and calcium had 7 times more cadmium in the upper part of the intestine than rats fed an adequate supply of these minerals. In addition, the rate at which cadmium moved out of the intestine was much slower in rats fed marginal zinc, iron, and calcium than those fed adequate amounts. The amounts of cadmium found in the liver and kidney were much higher when the rats ate diets with low compared with normal amounts of zinc, iron, and calcium. The results of this work show that marginal intakes of the zinc, iron, and calcium cause accumulation of cadmium in the upper GI tract and greater absorption into the body. The results suggest that food cadmium would be less toxic if the food or the diet contained ample amounts of the required mineral nutrients.
Technical Abstract: Dietary minerals Zn, Fe, and Ca are antagonistic to Cd absorption. We showed earlier that rats fed a rice-based diet with a marginal content of these nutrients absorbed more Cd than rats fed adequate Zn-Fe-Ca (Environ. Sci. & Technol. 36:2684-2692, 2002). The present experiment was designed to determine the effects of marginal dietary Zn, Fe, and Ca on the uptake and turnover of Cd in the GI tract. Two groups of weanling female rats (6/trt) were fed a diet containing 40% cooked, dried rice containing 0.6 mg Cd/kg. The diet of one group contained adequate Zn (35 mg/kg), Fe (30 mg/kg), and Ca (5,000 mg/kg), while the other group contained marginal Zn (6 mg/kg), Fe (9 mg/kg), and Ca (2,500 mg/kg). Rats were fed for 5 weeks and then orally dosed with 1 g of diet containing rice extrinsically labeled with 109**Cd. From 0.25 to 64 days after dosing, 109**Cd and non-labeled Cd concentrations were determined in intestinal segments. Shortly after dosing, the percent dose of 109**Cd was about 4 times higher in the duodenum of marginally fed rats than in control rats (10 vs. 40%, respectively). Sixty-four days after dosing, 109**Cd was 10 times higher in marginally fed rats than controls; however, of the amount at day-1, <0.1% remained at day-64. After 5 wks, the amount of non-labeled Cd in the duodenum of the marginally fed rats was 8 times higher than in control rats (2.9 vs. 24 ug/g dry wt., respectively). Cd concentrations in liver and kidney were 5 times higher in the marginally fed rats than controls (liver, 0.14 vs. 0.81 ug/g dry wt.; kidney, 0.92 vs. 4.7 ug/g dry wt., respectively). These data suggest that marginal intakes of Zn, Fe, and Ca cause hyper-accumulation of Cd in the duodenum, which results in a greater rate of Cd absorption, and a greater accumulation in the internal organs. Results are discussed in relation to mineral nutrient status and risk assessment of Cd in natural food sources.