There is regular mention in literature on iodine of endemic coastal goitre in areas of high seaweed consumption.
I have finally found a paper, as against mentions of the issue. The paper is titled
ENDEMIC COAST GOITRE IN HOKKAIDO, JAPAN
By
Hoji Suzuki, Tadashi Higuchi, Kunio Sawa,
Sachiya Ohtaki and Yoshihiko Horiuchi.
The full version of the paper includes a photo of a patient with an 'enormous' goitre; this was a real and serious issue. Urinary excretion of over 20mg a day of iodine was seen in five patients. Kelp collection was a local industry, and it formed a significant part of the diet. As discussed kelp often contains large amounts of iodine.
Interestingly when they were taken into hospital and put on a low thyroid diet some patients had a regression of their goitre.
The paper seems to suggest that iodine was actively being taken up by the thyroid, so uptake by the transporters was not the issue.
But 74.5% responded to thyroid treatment - so it looks as if something was blocking the activity of the thyroid; the thought occurred was that too much iodine as is generally suggested or something else . . .
All of which raises some important questions as to high iodine supplementation protocols, especially when reports of negative effects of high intake of iodine are limited in number. Are the negative effects of high iodine under reported or was the goitre in this instance due to to other factors? Does high iodine lead to serious thyroid dysfunction and goitre. These are very fundamental questions.
The answer to this question may lie in the unexamined issue that Hokkaido is an island with active 'volcanic' activity, and it is reported that the fumaroles are a source of both significant fluoride emissions, and fluoride deposits. Were the local water supplies, or supplies / wells / springs of individual patients high in fluorine, whereas in contrast was the hospital on a different supply?
A paper cited earlier in this thread suggests that relatively modest amounts of fouride even in the presence of iodine at 1mg/l in the water can cause fluorosis and goitre.
The Island of Hokkaido is listed as a high fluoride area (viz over 1.5mg/l), in a report called;
Fluoride in groundwater:
Probability of occurrence of excessive concentration on global scale
which cites this paper looking at volcanic fumerole activity on Hokkaido (one the most active regions in Japan) which says interalia
Acid alteration in the fumarolic environment of Usu volcano,
Hokkaido, Japan
F. Africano*, A. Bernard
The fumarolic environment studied is very rich in
fluorine. Whole rock fluorine contents range from 1 to
5 wt%. Aluminum fluorides, which are rare in nature,
are commonly observed in this fumarolic environment.
In the presence of fluorine and in acidic conditions,
the dominant aqueous Al species are fluoride
complexes, even in the presence of significant
amounts of sulfates in solution. Fluorine enrichment
in the altered silicates and in silica incrustations indicates
that fluorine plays an important role in the alteration
of the primary minerals and in the mobilization of
silica into the aqueous phase.
I surmise this could lead to high amounts of fluoride in water, which might be localised. Interestingly I could not find anything on flourosis and Hokkaido. Is or was fluorosis a problem in Hokkaido?
A combination of a diet high in marine products and volcanic activity would suggest a better than average mineral intake. I wonder if high mineral availability is protective against fluorosis.
There is no information about selenium, and apparently kelp whilst containing some selenium is not a good source, but apparently volcanoes are a significant source of selenium
It appears that goitre is not seen in all coastal Japanese communities, which would add further weight to the possibility the high fluoride rather than iodine was responsible for the goitre.
This appears to be a community that ate marine foods, seaweed, was in area that was likely to be well mineralised, probably had adequate selenium intake, and yet there was a high level of goitre. Volcanic areas are often associated with goitre so could fluoride be the cause even in a generally well nourished community. Might there be other possible contributory factors.
Might mercury have had a contributory role in the goitre incidence? Mercury poisoning in cattle in 1955 from seed treated with mercury fungicide. http://ci.nii.ac.jp/naid/110001075913 The goitre paper was written in 1965. Cranes local to Hokkaido were severely mercury contaminated. http://www.ncbi.nlm.nih.gov/pubmed/17713219Mercury Mercury deposits are found under northeastern Hokkaido.http://www.japantimes.co.jp/news/200.../#.UnV7t1N2FPI http://www.ncbi.nlm.nih.gov/pubmed/17713219 Mercury contamination of seafood in Japan reported as being at worrying levels.http://www.opsociety.org/issues/mercury-in-seafood Fumaroles may be a source of some mercury. Mercury contamination has been linked with thyroid dysfunction.
All of which raises very many questions, and most worrying of all, is fluoride sufficiently active in certain as yet unquantified circumstances to override even the effects of relatively high intakes of iodine ?