Cadmium Exposure in Pregnancy and Lactation in Relation to Iron Status

Abstract

Evidence is mounting that dietary cadmium may lead to renal tubular damage and progress to end-stage kidney disease. Because more cadmium is absorbed when iron stores are depleted and iron absorption is elevated in late pregnancy, this prospective study estimated blood and urinary cadmium concentrations and related them to iron status in 254 women 20 to 45 years of age who were followed from early in their pregnancies; 15% were current smokers. In addition, estimates were made in 106 placental and 32 cord blood samples collected at the time of delivery. Cadmium levels were determined by atomic absorption spectrophotometry. Nonsmoking women had a medium cadmium level of 0.16 μg/liter. Smokers, with levels 4 to 5 times higher, were excluded from further analyses. Both blood and urinary cadmium levels correlated negatively with the serum ferritin level and positively with the level of soluble transferrin receptor as well as the receptor/serum ferritin ratio. Age was not a confounding factor. More than half the women had exhausted their iron stores by late gestation, and 15% of them had tissue iron deficiency. The latter women had blood and urinary cadmium levels 40% to 50% higher than those without tissue iron deficiency during the period of lactation. The blood cadmium level increased approximately 20% from early gestation to lactation and the postlactation period. Only iron-depleted women had increased urine levels at the time of lactation, and they exhibited a further increase after lactation. Urinary cadmium increased with both advancing age and parity, which themselves interacted. Total placental cadmium content (but not concentration) correlated with the soluble transferrin receptor/serum ferritin ratio in late gestation and with the receptor concentration in cord blood serum. These findings suggest that the increased cadmium burden in women compared with men is a result of pregnancy and low iron status. Those with low iron stores, particularly women having multiple pregnancies, may be at increased risk for developing osteoporosis. Cereals and vegetables, which frequently are recommended for health-related reasons, are the major dietary sources of cadmium.