Bioavailability as an issue in risk assessment and management of food cadmium: A review

Authors: Reeves, Phillip; Chaney, Rufus

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/7/2008
Publication Date: 7/15/2008
Citation: Reeves, P.G., Chaney, R.L. 2008. Bioavailability as an issue in risk assessment and management of food cadmium: A review. Science of the Total Environment. 398(1-3):13-19.

Interpretive Summary: Cadmium is a trace element found in most foods and the consumption of too much of this element might have negative effects on kidney function. Primarily, regulations restricting the amount of cadmium allowed in food are based on how much cadmium there is in the food and not on whether the cadmium can be absorbed into the body. Work in our laboratory shows that low intakes of natural mineral nutrients such as zinc, iron, and calcium increase the absorption of cadmium up to 10-fold. Some grains, such as polished rice do not contain high amounts of cadmium. People who consume this rice as a staple food absorb more cadmium unless they also consume adequate amount 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. We also 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 suggest that food cadmium would be less toxic if the food or the diet contained ample amounts of these required mineral nutrients. A more complete understanding of how cadmium absorption from foods is regulated would help resolve food safety questions and provide the support for badly needed international policies regarding allowable cadmium levels in crops and foods.

Technical Abstract: The bioavailability of cadmium (Cd) from food could be an important determinant of the risk potential of dietary Cd to the consumer. This review summarizes recent work that describes the effects of marginal deficiencies of the essential nutrients zinc (Zn), iron (Fe), and calcium (Ca) on the enhancement of absorption and organ accumulation and retention of dietary Cd in laboratory animals. These marginal deficiencies enhanced Cd absorption as much as ten-fold from diets containing low Cd concentrations similar to that consumed by some human populations. This implies that if these populations also were nutritionally marginal with respect to Zn, Fe, and Ca, their risk of Cd disease might be much higher than if they were nutritionally adequate. Results from these studies also suggest that the bioavailability of Cd is different for different food sources. This has implications for the design of food safety rules for Cd in that if the dietary source plays such a significant role in the risk of Cd, then different foods would require different Cd limits. Lastly, the importance of food-level exposures of Cd and other potentially toxic elements in the study of risk assessment are stressed. Most foods contain low concentrations of Cd that are poorly absorbed, and it is not relevant or practical to use toxic doses of Cd in experimental diets to study food-Cd risks. A more comprehensive understanding of the biochemistry involved in the bioavailability of Cd from foods would help resolve food safety questions and provide the support for a badly needed advance in international policies regarding Cd in crops and foods.