Breast Milk Iodine and Perchlorate Concentrations in Lactating Boston-Area Women

Context: Breastfed infants rely on adequate maternal dietary iodine intake. Objective: Our objective was to measure breast milk iodine and perchlorate, an inhibitor of iodide transport into the thyroid and potentially into breast milk, in Boston-area women. Participants: The study included 57 lactating healthy volunteers in the Boston area. Measurements: Breast milk iodine and perchlorate concentrations and urine iodine, perchlorate, and cotinine concentrations were measured. For comparison, iodine and perchlorate levels in infant formulae were also measured. Results: Median breast milk iodine content in 57 samples was 155 μg/liter (range, 2.7–1968 μg/liter). Median urine iodine was 114 μg/liter (range, 25–920 μg/liter). Perchlorate was detectable in all 49 breast milk samples (range, 1.3–411 μg/liter), all 56 urine samples (range, 0.37–127 μg/liter), and all 17 infant formula samples (range, 0.22–4.1 μg/liter) measured. Breast milk iodine content was significantly correlated with urinary iodine per gram creatinine and urinary cotinine but was not significantly correlated with breast milk or urinary perchlorate. Conclusions: Perchlorate exposure was not significantly correlated with breast milk iodine concentrations. Perchlorate was detectable in infant formula but at lower levels than in breast milk. Forty-seven percent of women sampled may have been providing breast milk with insufficient iodine to meet infants’ requirements.