Iodine and eggs (and dairy)
(Eggs are a great food; chickens may not agree, but it appear the eggs and likely the chickens too are not what they once were, so chickens too should be concerned 
)
Traditionally eggs have been considered a good source of iodine; maybe because chickens concentrate iodine into eggs because it is essential to the development of healthy chicks.
This paper cited previously suggested that eggs may be associated with iodine deficiency in adolescent females in the UK.
http://her2support.org/vbulletin/showthread.php?t=53928
This puzzelled me for a few moments; maybe we do not feed hens as much fish meal as we used to I pondered, and mentally set the issue to one side.
I had forgotten the obvious that chickens drink water and eat food too, 
and so like us will be exposed to perchlorate, fluoride, chlorinated water, etc.
Perchlorate is apparently preferred to iodine by the iodine transporter found in the thyroid, reproductive tissues, and lots of other places, and that it would appear may apply to chickens too as chickens that ingest perchlorate concentrate it in their eggs at the expense of iodine/iodide. Did the IQ of the chickens suffer ; maybe that issue was not high on the researchers' agenda 
.
Our friend nitrate makes a showing too.
Was soy (a potential goitrogen) included in chicken meal; we do not know.
The conclusion was that the perchlorate in eggs did not add to the load in 2280 human individuals, but could goitrogens in chicken feed, and consequent increase in perchlorate and decrease in iodine go some way to explain the finding above that egg intake was related to iodine deficiency ?
And it occurs to me cows eat and drink too, and mammary glands concentrate iodine in milk at least in cows and people. Does perchlorate reduce the iodine content of milk? It appears it has the potential too - Oh dear - and does perchclorate get into milk; it appears it does - The amount may depend on the iodine intake of the cow . . . but it increase with increased perchlorate intake . . . which may not exceed the recommended daily intake maximum on its own . . . but perchlorate is found in water etc etc . . . back to disease by a thousand cuts.
http://www.ncbi.nlm.nih.gov/pubmed/18959414
J Agric Food Chem. 2008 Nov 26;56(22):10709-15. doi: 10.1021/jf8018326.
Perchlorate, nitrate, thiocyanate, and iodide levels in chicken feed, water, and eggs from three farms.
Blount BC, Ozpinar A, Alwis KU, Caudill SP, Gillespie JR.
Source
Division of Laboratory Sciences, Centers for Disease Control and Prevention, Atlanta, Georgia 30341, USA.
bkb3@cdc.gov
Abstract
Perchlorate is an inhibitor of iodide uptake that is found widely in the environment. Given the potential for perchlorate accumulation during egg formation and the widespread consumption of eggs, it is important to examine eggs as a source of exposure to perchlorate and other potential inhibitors of iodide uptake (nitrate and thiocyanate). This study was conducted to determine potential human exposure to perchlorate from eggs produced by chicken flocks consuming differing amounts of perchlorate. The mean concentrations of perchlorate (7.16 ( 1.99 microg/kg of dry weight), nitrate (2820 ( 2100 microg/kg of dry weight), thiocyanate (574 +/- 433 microg/kg of dry weight), and iodide (2980 ( 1490 microg/kg of dry weight) in eggs (n = 180) from 15 chicken houses on 3 U.S. farms were determined.
Chickens secreted into eggs an average of 23% of the perchlorate ingested from feed and water. Perchlorate levels in eggs were positively correlated with perchlorate intake (p < 0.001).
Increased intake of perchlorate, nitrate, and thiocyanate was associated with decreased iodide levels in eggs, possibly indicating a competitive transport mechanism, such as sodium-iodide symporter. It was estimated that egg consumption contributes minimal perchlorate (approximately 0.040 microg) compared to the average total intake of approximately 10.5 microg for U.S. adults. Additionally, it was found that egg consumption was not associated with increased perchlorate exposure in 2820 individuals from the National Health and Nutrition Examination Survey (p value for the difference of least-squares means, pDiff = 0.225).
From these findings it was concluded that, although chickens secrete perchlorate in eggs, eggs do not appear to be a significant source of perchlorate exposure for adults in the United States.
http://www.sciencedirect.com/science...22030273852464
Abstract
These experiments quantitate the relation between amount of perchlorate ingested and radioiodine transferred to milk of the cow when radioiodine is fed daily or after radioiodine administration ceases.
When radioiodine was given daily, graded doses of perchlorate, from 10 to 4,000 mg/day, increased plasma iodine in accord with Y = 88.1 X.052 (Y = % of control value and X is the daily dose of perchlorate in milligrams.) Curves for iodine-125 in milk and ratio of milk to plasma iodine-125 between the limits of 50 and 1,000 mg perchlorate daily were fitted by Y = 794.8 X-.525 and Y = 1,046.5X-.601; these same curves between 10 and 50 mg perchlorate daily were fitted by Y = 85.6 + .37 X and Y = 82.3 + .28 X. Between 1,000 and 4,000 mg perchlorate, these curves had a slope of 0. These data indicate that perchlorate can inhibit the iodide-transfer mechanism of the mammary gland of the cow and that a ratio of milk to iodine of .2 indicates complete blockage of this transfer.
Administration of 1 g of perchlorate daily leads to 55% less radioiodine being transferred to milk after administration of iodine 125 has ceased.
Also see for cows with iodine in feed and on equipment to prevent matitis
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1275600/
Conclusion; Nerds (me et al), cows and chickens may too need more iodine than they used to because of exposure to dietary goitrogens.