http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=pubmed&dopt=AbstractPlus&list_uids=15142639

Med Hypotheses. 2004;62(6):871-5.
Nutrition, evolution and thyroid hormone levels - a link to iodine 
deficiency disorders?
Kopp W.
Source

Diagnostikzentrum Graz, Mariatrosterstrasse 41, 8043 Graz, Austria. 
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Abstract

An increased iodine requirement as a result of significant changes in 
human nutrition rather than a decreased environmental iodine supply is 
suggested to represent the main cause of the iodine deficiency disorders 
(IDD). The pathomechanism proposed is based on the fact that serum 
concentrations of thyroid hormones, especially of trijodothyronine (T3), 
are dependent on the amount of dietary carbohydrate. High-carbohydrate 
diets are associated with significantly higher serum T3 concentrations, 
compared with very low-carbohydrate diets. While our Paleolithic 
ancestors subsisted on a very low carbohydrate/high protein diet, the 
agricultural revolution about 10,000 years ago brought about a 
significant increase in dietary carbohydrate. These nutritional changes 
have increased T3 levels significantly. Higher T3 levels are associated 
with an enhanced T3 production and an increased iodine requirement. The 
higher iodine requirement exceeds the availability of iodine from 
environmental sources in many regions of the world, resulting in the 
development of IDD.

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So if we eat a true paleo diet we would not need to supplement, except 
that iodine chelates or somehow removes toxins in our environment, such 
as the other halogens and mercury.

William