Which of the following is the 'Active form' of Vitamin D that acts as a hormone in the body?

RML Lucknow - 2021

Applied Nutrition & Dietetics

Easy

Appeared in: RML Lucknow - 2021

Explanation

1,25-dihydroxycholecalciferol, also known as Calcitriol, is the physiologically active hormone form of Vitamin D.
It is the final product of a two-step hydroxylation process that occurs first in the liver and then in the kidneys.
As a hormone, Calcitriol acts on target tissues—primarily the intestine, bones, and kidneys—to increase plasma calcium and phosphate levels.
Its synthesis is tightly regulated by parathyroid hormone (PTH), serum calcium, and phosphate levels, which is characteristic of a hormone.

Option A: Cholecalciferol (Vitamin D₃) is a prohormone, meaning it is an inactive precursor. It must be metabolized in the liver and kidneys to become active.
Option B: Ergocalciferol (Vitamin D₂) is also an inactive precursor. It is derived from plant sources and fortified foods and requires the same activation steps as Cholecalciferol.
Option D: 25-hydroxycholecalciferol (Calcidiol) is an intermediate metabolite. While it is the major circulating and storage form of Vitamin D, it is not the final, fully active hormone.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Metabolism and active form of Vitamin D as background academic context rather than a clinical decision trigger.
Nurses play a key role in identifying patients at risk for Vitamin D deficiency, such as those with chronic kidney disease, liver failure, malabsorption syndromes, or limited sun exposure.
Understanding the activation pathway is crucial because patients with chronic kidney disease cannot produce Calcitriol. They often require supplementation with the active form to prevent renal osteodystrophy and manage calcium levels.
Patient education includes advising on safe sun exposure, dietary sources of Vitamin D, and the importance of adherence to prescribed supplements.

How to Approach the Question

This is a factual recall question testing knowledge of biochemistry and physiology.
Identify the keywords in the question: 'Active form', 'Vitamin D', and 'hormone'.
Recall the metabolic pathway for Vitamin D activation. Remember that it is a two-step process involving two different organs.
Step 1 (Liver): The precursor (Cholecalciferol/Ergocalciferol) is converted to the storage form (25-hydroxycholecalciferol).
Step 2 (Kidney): The storage form is converted to the active hormone (1,25-dihydroxycholecalciferol).
Evaluate each option against this pathway. Eliminate the precursors and the intermediate storage form to find the final active hormone.

Concept Tested & Keywords

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