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iodine uptake in thyroid

I'm looking for some information on the uptake of iodine in the thyroid 
for adults (chronic exposures), more specifically, the relative or 
fractional uptake of iodine when compared to the normal amount of iodine 
ingested.  ICRP 56 uses the value of 0.3.  Dunning and Schwarz (Health 
Phys 40 (5) 1981) provide estimates of the distribution of iodine uptake 
which shows that the mean is 0.19, median 0.17, and the mode 0.15.  The 
value of 0.3 probably represents about the 95% upper bound.  I'm 
uncertain as to whether this value is appropriate for chronic exposures 
to radioactive iodine (I-129) that represent anywhere from 50% to 200% of 
the normal, daily requirements of iodine (roughly 150 ęg/d ingested -    
30 ęg used (Guyton and Hall - Textbook of Medical Physiology)).  Could 
the fractional uptake simply be estimated as the amount needed over the 
amount ingested, i.e., does the body maintain the iodine concentration in 
the body under homeostatic control?

Any insight, references, etc., would be appreciated.

Andrew H. Thatcher, MSHP, CHP
Washington Department of Health
360-236-3255 voice*
360-236-2255 fax*
*new number