Mineral intake vital to prevent cadmium poisoning

Insufficient intake of minerals iron, zinc and calcium in the diet can lead to unhealthy increases in cadmium uptake in the kidney and liver, according to scientists from the USDA's Agricultural Research Service.

The researchers wanted to assess whether staple grains such as rice, wheat and maize could help prevent the bioavailability of cadmium when taken in association with the minerals.

Rats fed a rice-based diet were tested with low levels and combinations of iron, zinc and calcium, along with cadmium at levels that actually occur in foods. Rats fed higher amounts of the same mineral or minerals served as control groups.

The scientists discovered that the rats fed only low levels of iron or calcium had a threefold higher retention of cadmium than controls. But rats fed low levels of all three - zinc, iron and calcium together - retained eight times more cadmium than rats fed higher levels minerals.

The research suggests that populations exposed to only low 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, the ARS said.

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 have hinted at the importance of zinc, iron and calcium's preventative effects on the absorption of cadmium, but the ARS said that those studies had used unnaturally high quantities of the minerals and looked only at intestinal absorption.

The current study, which appears in the July issue of Environmental Science & Technology​, was conducted by research chemist Philip G. Reeves and research agronomist Rufus L. Chaney.