According to this fascinating article, insulin resistance is behind degenerative disease including unrecognized hypothyroidism.

http://articles.mercola.com/sites/ar...-part-one.aspx

"The thyroid produces mostly T4. T4 goes to mostly to the liver and is converted to T3. We are getting the idea that insulin controls a lot of what goes on in the liver, and the liver is the primary organ that becomes insulin resistant.

When the liver can no longer listen to insulin, you can‘t convert T4 to T3 very well. In people who are hyperinsulinemic with a thyroid hormone that comes back totally normal, it is important to measure their T3. Just as often as not, their free T3 will be low, but get their insulin down and it comes back up."