Iodine and Estrogen metabolism

I've been thinking about how iodine is reported to convert estradiol and estrone into estriol and I'm a bit confused. The only pathway that estriol is metabolized from is 16-hydroxyestrone. Does this mean that iodine stimulates and encourages the production of 16-hydroxyestrone? Or does it just convert the existing 16-hydroxyestrone that the body naturally makes into estriol? If taking iodine lowers estradiol and estrone and increases estriol, it would seem that it would also cause a a rise in 16-hydroxyestrone since this is the only way estriol can be formed.

I just don't understand how estriol can increase without its precursor also increasing. If this is the case, wouldn't it be much safer to take DIM since it doesn't cause the levels of a carcinogenic estrogen to rise?

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Can anyone clear this up? CS?