QS Study

Iodine Metabolism

Iodine is a fundamental micronutrient essential at all stages of life; fetal life and early childhood being the most significant phases of the condition. Iodine enters the body primarily as iodide in food and in drinking water. Iodine is metabolized in the human body through a series of stages involving the hypothalamus, pituitary, thyroid gland, and blood. A fit mature body contains 15-20 mg of iodine, 70-80% of which is stored in the thyroid gland.

Fig: Iodine Metabolism

 (1) Ingestion of iodine and absorption as iodide:

It is the raw material essential for thyroid hormone. Ingested iodine is converted to iodide and absorbed.

(2) Requirement: The minimum daily iodine intake that will maintain normal thyroid function is 150 μgm in adults.

(3) Plasma I level: The normal plasma iodine level is about 0.3 μg/dl.

(4) The fate of absorbed iodide:

(a) About 120 μgm/dl enter the thyroid at normal rates of TH synthesis and secretion. The thyroid secretes 80 μgm /di as iodine in T3 and T4. 40 μgm of I per day diffuses into ECF.

The secreted T3 and T4 are metabolized into liver and other tissue, with the release of 60 μgm of I per day into ECF.

Some thyroid hormones are secreted through bile. So iodine is reabsorbed (enterohepatic circulation). Net loss of I in the stool is approximately 20 μgm/day.

About 480 μgm of I per day is taken up by the kidney is excreted in the urine.

(5) The total amount of I entering ECT

Total amount of I entering to the ECT as thus 500 + 40 + 60 = 600 μgm/dl. 20 % of this is used for Thyroid, whereas 80% is excreted in the urine.