Effects of cadmium intake on bone metabolism of mothers during pregnancy and lactation.

Cadmium (Cd) is a heavy metal that exists ubiquitously in the environment, and it interacts with essential elements such as zinc, copper, iron, and calcium (Ca). Particularly, Cd interferes with Ca and vitamin D metabolism in bone kidney and intestine. The interaction between Cd and Ca in bone, intestine, and kidney may result in the disorder of bone metabolism. On the other hand, pregnancy and lactation are also important physiological factors affecting bone metabolism in the mother. Ca absorption is decreased by competition with Cd in the intestine, and more Ca is released from maternal bone and transferred to neonate by lactation. In the intestine, Cd uptake competes with Ca uptake. Cd causes a marked decrease in bone density compared to the normal decrease in bone mineral density during lactation. Lactation is an important factor contributing to the decrease in bone mineral density and Cd has an additive effect of decreasing bone metabolism of mother animal, although the Cd intake level is relatively low (approximately 3-14 microgCd/kg/day). The relationship among maternal Cd intake, renal function and bone metabolism and the interaction between Cd and Ca during lactation are reviewed herein, together with additional data obtained recently in our laboratory.