The synthesis of which vitamin is initiated in the skin upon exposure to ultraviolet light?

HSSC Staff Nurse - 2015

Applied Nutrition & Dietetics

Easy

Appeared in: HSSC Staff Nurse - 2015

Explanation

The skin synthesizes Vitamin D when exposed to ultraviolet B (UV-B) radiation from sunlight.
A precursor molecule in the skin, 7-dehydrocholesterol, is converted into cholecalciferol (Vitamin D₃) through a photochemical reaction.
This initial form of Vitamin D then travels to the liver and kidneys to be converted into its active form, which is essential for calcium and phosphorus absorption.
Deficiency in Vitamin D can lead to bone disorders such as rickets in children and osteomalacia in adults.

Option A: Vitamin A is a fat-soluble vitamin obtained from dietary sources (e.g., carrots, liver) and is not synthesized in the skin through UV light exposure.
Option B: Vitamin C is a water-soluble vitamin that must be obtained from the diet (e.g., citrus fruits). The human body cannot synthesize it.
Option D: Vitamin K is a fat-soluble vitamin obtained from dietary sources (e.g., leafy greens) and is also produced by bacteria in the gut. It is not synthesized in the skin.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Vitamin synthesis in the skin as background academic context rather than a clinical decision trigger.
Nurses play a key role in educating patients about the importance of safe sun exposure for adequate Vitamin D production, while also advising on the risks of excessive sun exposure, such as skin cancer.
Assessment for Vitamin D deficiency is crucial in high-risk groups, including the elderly, individuals with limited sun exposure (e.g., institutionalized patients), people with dark skin, and those with malabsorption disorders.
What if? If a patient has severe chronic kidney disease, their ability to convert Vitamin D to its active form (calcitriol) is impaired. In this case, simple sun exposure or standard Vitamin D supplements would be insufficient. The patient would require supplementation with an active form of Vitamin D, like calcitriol, to prevent renal osteodystrophy.

How to Approach the Question

Identify the key terms in the question: 'synthesis', 'vitamin', 'skin', and 'ultraviolet light'.
Recognize that this combination points to a specific and well-known physiological process.
Systematically review the options based on your knowledge of vitamin sources.
Recall that Vitamin A is from diet (carrots, liver), Vitamin C is from diet (citrus fruits), and Vitamin K is from diet (leafy greens) and gut bacteria.
Conclude that Vitamin D is the only vitamin among the choices whose synthesis is initiated in the skin by UV light.
This process makes Vitamin D unique, as it functions like a hormone that the body can produce itself under the right conditions.

Concept Tested & Keywords

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