It’s important to understand the connection between TSH and iodine supplementation so that you are not surprised if your blood levels change when you start supplementing with iodine.
TSH may increase in the start of iodine supplementation because TSH stimulates the thyroid gland to produce thyroid hormones. TSH also stimulates the body’s production of iodine transport molecules called the sodium-iodide symporter (NIS) and NIS shuttles iodine from the bloodstream into the thyroid cell in order for the cell to use the iodine to make thyroid hormones. Increase in TSH without clinical signs of hypothyroidism (fatigue, hair loss, headaches) and normal T3 and T4 does not indicate hypothyroid condition. TSH usually increased for 6-9months.
Taking thyroid hormones with iodine deficiency present can worsen iodine deficiency.