**Core Concept**
Iodine is an essential trace element that plays a critical role in the synthesis of thyroid hormones (T3 and T4) in the thyroid gland. Iodine deficiency can lead to hypothyroidism and cretinism in severe cases.

**Why the Correct Answer is Right**
Iodine is primarily absorbed from the gastrointestinal tract, particularly in the small intestine. It is then transported to the thyroid gland, where it is oxidized and incorporated into thyroglobulin, a protein that serves as a substrate for thyroid hormone synthesis. Iodide ions (I-) are essential for the production of monoiodotyrosine (MIT) and diiodotyrosine (DIT), which are subsequently coupled to form triiodothyronine (T3) and thyroxine (T4). The thyroid hormones are then released into the bloodstream and distributed to peripheral tissues.

**Why Each Wrong Option is Incorrect**
**Option A:** Iodine supplementation is a common practice in regions with iodine deficiency, which is a public health concern worldwide. This statement is true.
**Option B:** Iodine is primarily excreted in the urine, with a small amount being excreted in the feces. This statement is true.
**Option C:** Iodine deficiency can lead to hypothyroidism, goiter, and cretinism in severe cases. Iodine supplementation is essential to prevent these conditions. This statement is true.

**Clinical Pearl / High-Yield Fact**
Iodine deficiency is a significant public health concern worldwide, particularly in regions where iodized salt is not widely available. Iodine supplementation can prevent hypothyroidism, goiter, and cretinism, and is essential for the production of thyroid hormones.

**Correct Answer:** D.