Which Fat soluble vitamin is functioning like a “Hormone”:
**Core Concept**
The question is testing the student's knowledge of fat-soluble vitamins and their functions, specifically which one acts like a hormone. **Vitamin D** is a fat-soluble vitamin that plays a crucial role in the body.
**Why the Correct Answer is Right**
**Vitamin D** acts like a hormone because it is synthesized in the skin upon sunlight exposure and then undergoes hydroxylation in the liver and kidney to form its active form, **1,25-dihydroxyvitamin D**. This active form then binds to the **vitamin D receptor**, a nuclear receptor, to regulate gene expression.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while **Vitamin A** is a fat-soluble vitamin, it does not function like a hormone in the same way **Vitamin D** does.
**Option B:** Incorrect as **Vitamin E** is primarily an antioxidant.
**Option C:** Incorrect because **Vitamin K** is mainly involved in blood clotting.
**Clinical Pearl / High-Yield Fact**
Remember, **Vitamin D** deficiency can lead to **rickets** in children and **osteomalacia** in adults, highlighting its importance in bone health.
**Correct Answer:** D. Vitamin D