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The Effect of Calcium and Phosphorus on the Metabolism of Lead

Division of Animal Nutrition, University of Illinois, Urbana

The effect of varying the concentration of calcium and phosphorus in diets containing low concentrations of lead (16 to 32 p.p.m.) on the retention of lead was investigated in a series of five experiments involving 128 growing or adult rats. In some of these experiments the retention of calcium and phosphorus was also measured. All mineral retentions were measured by carcass analysis. An essential feature of the experiments was the equalization of the food intakes of rats on comparable diets, thus permitting the interpretation of the results in terms solely of the relative compositions of the diets.

The results obtained appear to warrant the following conclusions:

1. A low content of calcium or of phosphorus or of both in the diet induces a high retention of lead in comparison with diets containing higher mineral levels. In fact, the only method of securing lead storage in adult rats on the moderate concentration of dietary lead used (32 p.p.m.) is to lower the calcium content of the diet to inadequate or borderline levels.

2. Excessive dietary levels of calcium and phosphorus are not appreciably more protective against the assimilation of lead by the body than are levels approximating the requirements. This statement applies only to the moderate levels of dietary lead employed.

3. Under the imposed conditions of variable dietary concentrations of calcium and phosphorus, the retention of calcium runs in a diametrically opposite direction to the retention of lead.

4. Under conditions of practical nutrition, an adequate intake of calcium and of phosphorus presumably protects the body against appreciable assimilation of the low levels of dietary lead involved in the usual lead hazard of modern life. This protection is more effective in the adult than in the adolescent for any given concentration of calcium and phosphorus, possibly because the mineral metabolism of the bone trabeculae is considerably less intense in the adult than in the growing organisms.