Abstract
Breast-fed infants may depend solely on an adequate supply of iodine in breast milk for the synthesis of thyroid hormones which are essential for optimal growth and cognitive development. This is the first study to measure breast milk iodine concentration (BMIC) among lactating women in Western Australian (n = 55). Breast milk samples were collected between 2014 and 2015 at a mean (±SD) of 38.5 (±5.5) days post-partum. The samples were analysed to determine median BMIC and the percentage of samples with a BMIC < 100 µg/L, a level considered adequate for breast-fed infants. The influence of (a) iodine-containing supplements and iodised salt use and (b) consumption of key iodine-containing foods on BMIC was also examined. The median (p25, p75) BMIC was 167 (99, 248) µg/L and 26% of samples had a BMIC < 100 µg/L. Overall, BMIC tended to be higher with iodine-containing supplement usage (ratio 1.33, 95% confidence interval (CI) (1.04, 1.70), p = 0.030), cow’s milk consumption (ratio 1.66, 95% CI (1.23, 2.23), p = 0.002) and lower for Caucasians (ratio 0.61, 95% CI (0.45, 0.83), p = 0.002), and those with secondary school only education (ratio 0.66, 95% CI (0.46, 0.96), p = 0.030). For most women, BMIC was adequate to meet the iodine requirements of their breast-fed infants. However, some women may require the use of iodine-containing supplements or iodised salt to increase BMIC to adequate levels for optimal infant nutrition.
Highlights
Iodine, an essential nutrient, is required by humans for the synthesis of thyroid hormones which are vital for normal growth and development [1,2]
Two initiatives introduced in response to the re-emergence of this public health issue are the mandatory fortification of all bread with iodised salt in 2009 [16] and the 2010 National Health and Medical Research Council recommendation that all pregnant and breastfeeding women take a daily supplement containing 150 μg of iodine [17]
breast milk iodine concentration (BMIC) levels were below the suggested adequate cut-off (100 μg/L) for 26% of women, indicating some infants may be at risk for iodine deficiency, especially if exclusively breast-fed as is recommended
Summary
An essential nutrient, is required by humans for the synthesis of thyroid hormones which are vital for normal growth and development [1,2]. Intake (AI) of 90 μg/day for infants aged 0–6 months [7] This is achieved by a physiological response during breastfeeding whereby iodine is strongly concentrated by the lactating mammary gland due to the increased expression of the sodium iodide symporter, the main iodine transporter in lactating breast cells [8]. Two initiatives introduced in response to the re-emergence of this public health issue are the mandatory fortification of all bread (except organic) with iodised salt in 2009 [16] and the 2010 National Health and Medical Research Council recommendation that all pregnant and breastfeeding women take a daily supplement containing 150 μg of iodine [17] Despite this recommendation, only two studies have examined the iodine content of breast milk in Australia to assess either iodine provision to breastfed infants or maternal iodine status. We investigated the influence of iodine-containing supplements and iodised salt use, as well as the consumption of key iodine-containing foods, on this biomarker of iodine status
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