In patients with mild deficiencies of iodine and selenium, the levels of these elements in thyroid tissue change in ways that relate to the amount of thyroid-stimulating hormone present, suggesting that nutrient levels and thyroid activity are linked in diseased tissue.

In people with thyroid diseases, higher levels of TSH in the blood are linked to lower amounts of iodine, selenium, and zinc in the thyroid tissue, indicating that thyroid function may be related to the balance of these trace elements.

In people with thyroid disease, the levels of iodine, selenium, and zinc in thyroid tissue are typically within the range seen in earlier studies, even though the general population may have slightly low levels of iodine and selenium.

People with low selenium levels have lower amounts of free T3 hormone in their blood compared to those with normal thyroid function, but their free T4 and TSH levels do not consistently rise, suggesting the issue is not with the thyroid gland itself but with how the body converts thyroid hormones in peripheral tissues.

In people with low selenium levels, taking selenium supplements lowers free T4 and the ratio of free T4 to free T3 while raising free T3 levels, suggesting that selenium plays a role in how the body converts thyroid hormones and that this process can improve with supplementation.

In the thyroid gland, iodine levels differ greatly from one follicle to another, while selenium and zinc levels remain relatively consistent across follicles, suggesting iodine is actively regulated in a variable way, whereas selenium and zinc are distributed more evenly.