Dietary Mineral Status Key to Cadmium Toxicity

A lack of dietary iron, zinc and calcium results in unhealthy increases in cadmium uptake into the kidney and liver, Agricultural Research Service scientists report. Staple grains such as rice, wheat and maize differ greatly in their levels of these three key minerals that counteract the absorption, or bioavailability, of cadmium.

The scientists examined test rats fed a rice-based diet with various marginal levels and combinations of iron, zinc and calcium, along with cadmium at levels that actually occur in foods. Rats fed adequate amounts of the same mineral or minerals served as control groups. Rats fed only marginal iron or calcium had a threefold higher retention of cadmium than controls. But rats fed marginal levels of all three--zinc, iron and calcium-- retained a whopping eight times more cadmium than rats fed adequate minerals.

The research suggests that populations exposed to marginal mineral intakes are at greater risk of absorbing increased amounts of cadmium than well-nourished populations exposed to similar amounts of cadmium. The study could have serious implications for people who eat subsistence rice diets too low in zinc, iron or calcium.

In areas of Japan and China where rice is grown on soils contaminated by mining wastes, people have suffered adverse health effects from cadmium intake. Yet people in other countries who consumed similar amounts of cadmium in foods grown on more highly contaminated soils did not experience adverse effects from cadmium intake; those foods contained adequate zinc, iron, and calcium to retard cadmium absorption into the body.

Previous studies only hinted at the importance of zinc, iron and calcium's preventative effects on the absorption of cadmium. Those studies employed unnaturally high quantities of the minerals and looked only at intestinal absorption.

The current study, which appears in July's Environmental Science & Technology, was conducted by research chemist Philip G. Reeves and research agronomist Rufus L. Chaney, both with ARS, the U.S. Department of Agriculture's chief scientific research agency.