7%. Rats fed the low-calcium diet, which contained only 12ppm lead, had blood and tissue concentrations of lead similar to those in rats receiving 200ppm lead on a normal-calcium diet. This study also showed that the increase in lead content of the kidneys was considerably greater than the increase in bone lead. The importance of this is that the toxic effects of lead are related to blood lead concentrations and that low dietary calcium increases the concentration of lead in critical organs. Many other experimental studies have shown that absorption of lead by the gastrointestinal tract is inversely related to calcium content of the diet. More recently, Bogden et al (9) showed an inverse relationship between brain lead and dietary calcium, confirming that nutritional deficiency of calcium not only elevates blood lead concentrations but also increases lead in the critical organ for toxicity in infants and young children.
Although it is not possible to mimic the animal studies in people, Zeigler et al (10) conducted multiple (three to eight) 72-hour metabolic balance studies on each of nine infants. Lead and calcium intakes from milk and other food items were measured and lead retention calculated as the difference between intake and excretion. The results of the study showed an inverse relationship between dietary calcium and lead absorption and retention. It has also been shown that milk alone may not be an effective source of calcium for this purpose because other dietary constituents of milk such as lactose and fat may actually enhance lead absorption. Mahaffey et al (12) reviewed the relationship between blood lead concentrations and dietary calcium intake in = 3000 children examined as part of the second National Health and Nutrition Examination Survey (NHANES 11). A significant and independent inverse association was observed between dietary calcium intake, estimated from dietary recall data, and blood lead concentrations in this large, stratified, national probability sample.