Hashis really isnt the result of Iodine deficiency, more selenium and other nutrients used in the breakdown of the toxic byproducts of thyroid hormone production which Iodine enables.
So while many people will blame adding Iodine as the cause, the problem isnt the iodine, its that adding the iodine ALLOWS the body to produce NEEDED levels of thyroid hormones. The problem isnt the body utilizing the iodine thats the real issue, its the body not having what it needs to deal with the byproducts OF the body using the iodine.
Adding iodine to the body when there isnt ample nutrients to deal with byproducts is like running a car in a closed garage. Sooner or later the exhaust will build up and cause damage to living beings in the garage and ultimately also reduce the engines ability to run as the oxygen is consumed and replaced with exhaust gases.
A body lacking iodine is like a car sitting in a garage that isnt running. No harm no foul but your never gonna get to the grocery store either.
Adding iodine is like starting the car but opening the garage door. You need to open the door so the toxic gases dont overcome you.
Adding iodine AND required nutrients is whats really needed and thats like pulling the car out of the garage and actually being able to use it.