Widespread iodine deficiency in breast milk in the US ?
It is often suggested in material that iodine status in the US is better than the UK; I have not looked for data so have no data to back this up. The above figures from the Avon study would suggest levels of iodine in breast milk are also likely to be low in the UK
Temporal Patterns in Perchlorate, Thiocyanate, and Iodide Excretion in Human Milk
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1817678/
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Breast milk–iodine content is considered sufficient when levels are 150–180 μg/L (Delange 2004). Milk samples provided by most women in our previous study (Kirk et al. 2005) fell far short of this standard.
The median iodide level in human milk from 23 donors residing in 15 different states (Kirk et al. 2005) was 33.5 μg/L, and only 4 samples fell within the recommended level. We have therefore been concerned that lactating women in the United States may not be consuming sufficient iodine to meet the needs of their breast-fed infants."
The paper also expresses concerns about the effect of perchlorate on the iodine content of breast milk and the potential effect of perchlorate in breast milk. The paper observes that little is know about the issues.
It appears that perchlorate on a unit weight basis is a comparatively powerful competitive inhibitor of iodine uptake; the effect will depend on the amount taken up - so other blocking factors by be more important if and when present in much greater quantity eg food goitrogens - the effect will also depend on the amount of iodine in the diet; the lower the amount the great susceptibility to competitive blockers - fluoride appears to work by a different blocking mechanism (see above).
"Exposure to perchlorate and other iodide transport inhibitors may increase the risk of iodine deficiency among infants. The sodium–iodide symporter (NIS) is 30-fold more selective for perchlorate than for iodide and is reportedly 9–100 times as potent as thiocyanate in inhibiting iodide uptake (Dohan et al. 2003; Tonacchera et al. 2004). Perchlorate and other iodide transport inhibitors such as thiocyanate thus likely reduce transfer of iodide to breast milk at the mammary NIS."
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