Cadmium interacts with the transport of essential micronutrients in the mammary gland—A study in rural Bangladeshi women

Although the concentrations of the toxic metal cadmium in breast milk are generally low (<1 μg/L), experimental studies indicated neurobehavioral and endocrine effects in the suckling offspring. The aim of the present study was to elucidate how cadmium is transported to breast milk by assessing interactions with essential micronutrients. The study is nested into a food and micronutrient supplementation trial conducted among pregnant women in Matlab, a rural area in Bangladesh, where malnutrition is prevalent and the cadmium exposure is relatively high. We measured cadmium in breast milk (BM–Cd; median 0.14 μg/kg; range <0.050–1.0 μg/kg), in erythrocytes (Ery–Cd; median 1.5 μg/kg; range 0.46–4.8 μg/kg) and in urine (U–Cd; median 0.63 μg/L; range 0.050–4.5 μg/L), using inductively coupled plasma mass spectrometry (ICPMS). We found a significant positive association between Ery–Cd and BM–Cd and a breast milk-plasma ratio of ∼3–4, indicating no barrier against cadmium transport from plasma to breast milk. BM–Cd was positively associated with manganese (rs = 0.56; p < 0.01) and iron (rs = 0.55; p < 0.01) in breast milk, but not with plasma ferritin. On the other hand, BM–Cd was negatively associated with BM–Ca (rs = −0.17; p = 0.05), indicating that cadmium inhibits the transport of calcium to breast milk. In conclusion, the present study may indicate that cadmium shares common transporters with iron and manganese for transfer to breast milk, but inhibits secretion of calcium to breast milk.