Q: Which fat-soluble vitamin acts as a hormone to regulate calcium and phosphorus homeostasis, and what is the equation for its activation?

Vitamin D; $$\text{Cholecalciferol} \xrightarrow{\text{Liver}} \text{25(OH)D} \xrightarrow{\text{Kidney}} \text{1,25(OH)}_2\text{D}$$

Question 1

A patient presents with night blindness and dry, keratinized epithelial tissue. Which vitamin deficiency is most likely responsible, and what is the underlying mechanism?

Accepted Answer

Vitamin A deficiency; impaired cell differentiation and rhodopsin synthesis

Question 2

Which of the following best explains why fat-soluble vitamins are more likely to cause toxicity than water-soluble vitamins?

Accepted Answer

They are stored in body fat and not easily excreted

Question 3

A newborn develops hemolytic anemia. Which vitamin deficiency is most likely, and why are newborns particularly at risk?

Accepted Answer

Vitamin E; due to limited stores and poor fat absorption

Question 4

Which of the following foods is the richest source of preformed vitamin A (retinol)?

Accepted Answer

Liver

Question 5

A patient taking warfarin is advised to maintain a consistent intake of which vitamin, and why?

Accepted Answer

Vitamin K; because it is required for synthesis of blood-clotting proteins

Question 6

Which fat-soluble vitamin acts as a hormone to regulate calcium and phosphorus homeostasis, and what is the equation for its activation?

Accepted Answer

Vitamin D; $$	ext{Cholecalciferol} \xrightarrow{	ext{Liver}} 	ext{25(OH)D} \xrightarrow{	ext{Kidney}} 	ext{1,25(OH)}_2	ext{D}$$

Question 7

A person consumes large amounts of carrots and develops orange-colored skin but no other symptoms. What is the condition and which vitamin is involved?

Accepted Answer

Hypercarotenemia; vitamin A (as beta-carotene)

Question 8

Which vitamin deficiency is associated with increased risk of osteoporosis due to its role in bone protein synthesis?

Accepted Answer

Vitamin K

Question 9

A patient presents with high blood calcium, kidney stones, and soft tissue calcification. Which vitamin toxicity is most likely?

Accepted Answer

Vitamin D

Question 10

Which of the following best describes the antioxidant function of vitamin E?

Accepted Answer

It protects polyunsaturated fatty acids in cell membranes from oxidative damage

Question 11

A child with a diet low in vitamin D develops bowed legs and pigeon breast. What is the diagnosis and the underlying biochemical mechanism?

Accepted Answer

Rickets; decreased calcium and phosphorus absorption

Question 12

Which fat-soluble vitamin is most likely to interfere with anticoagulant medications when taken in excess?

Accepted Answer

Vitamin E

Question 13

Which of the following statements about carotenoids is TRUE?

Accepted Answer

They can be converted to retinoids and may act as antioxidants

Question 14

Which vitamin is essential for the synthesis of prothrombin, and what is the consequence of its deficiency?

Accepted Answer

Vitamin K; hemorrhage

Question 15

A patient with a history of fat malabsorption is at risk for deficiencies in which group of vitamins, and why?

Accepted Answer

Vitamins A, D, E, and K; they require bile and dietary fat for absorption

Question 16

Which of the following best explains why vitamin D supplementation is recommended during winter months in northern latitudes?

Accepted Answer

Sunlight exposure is limited, reducing endogenous synthesis

Question 17

Which vitamin is directly involved in gene expression related to cell differentiation and immune function?

Accepted Answer

Vitamin A

Question 18

A patient presents with easy bruising and uncontrolled bleeding after a course of antibiotics. Which vitamin deficiency is most likely and why?

Accepted Answer

Vitamin K; reduced synthesis by intestinal bacteria

Question 19

Which of the following is a potential adverse effect of excessive preformed vitamin A intake during pregnancy?

Accepted Answer

Birth defects

Question 20

Which vitamin's deficiency is most likely to cause poor muscle coordination, weakness, and impaired vision in adults with poor fat absorption?

Accepted Answer

Vitamin E

Fat-Soluble Vitamins: Structure, Function, and Dietary Sources

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