Conversion of cholesterol into vitamin D MCQs With Answer

Conversion of cholesterol into vitamin D MCQs With Answer

Conversion of cholesterol into vitamin D is a fundamental biochemical and clinical topic for B.Pharm students. This SEO-focused introduction and question set covers the photochemical conversion of 7-dehydrocholesterol to previtamin D3, thermal isomerization to cholecalciferol (vitamin D3), hepatic and renal hydroxylations to 25‑hydroxyvitamin D and 1,25‑dihydroxyvitamin D, regulation by PTH, FGF23 and CYP enzymes, transport by vitamin D binding protein, pharmacokinetics, assays and clinical implications like deficiency, toxicity and drug interactions. These 50 MCQs with answers emphasize mechanisms, enzymes (CYP2R1, CYP27B1, CYP24A1), synthesis factors and therapeutic considerations for B.Pharm students. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which skin precursor is photochemically converted into previtamin D3 upon UVB exposure?

• Cholesteryl ester
• 7-dehydrocholesterol
• Lanosterol
• Desmosterol

Correct Answer: 7-dehydrocholesterol

Q2. What wavelength range of UV radiation is primarily responsible for the photoconversion of 7-dehydrocholesterol to previtamin D3?

• UVC (100–280 nm)
• UVB (290–315 nm)
• UVA (315–400 nm)
• Visible light (400–700 nm)

Correct Answer: UVB (290–315 nm)

Q3. After photochemical formation, previtamin D3 is converted to cholecalciferol by which process?

• Enzymatic hydroxylation
• Thermal isomerization
• Oxidative cleavage
• Conjugation with glucuronic acid

Correct Answer: Thermal isomerization

Q4. Cholecalciferol (vitamin D3) formed in skin is transported in blood primarily bound to which protein?

• Albumin
• Transferrin
• Vitamin D binding protein (DBP)
• Alpha-1 acid glycoprotein

Correct Answer: Vitamin D binding protein (DBP)

Q5. Which organ performs the primary 25-hydroxylation of cholecalciferol to form 25-hydroxyvitamin D?

• Kidney
• Liver
• Skin
• Intestine

Correct Answer: Liver

Q6. Which enzyme is considered the principal hepatic 25-hydroxylase for vitamin D metabolism?

• CYP27B1
• CYP2R1
• CYP24A1
• CYP3A4

Correct Answer: CYP2R1

Q7. The active hormonal form of vitamin D produced in the kidney is:

• 25-hydroxyvitamin D (25(OH)D)
• Cholecalciferol (vitamin D3)
• 1,25-dihydroxyvitamin D (1,25(OH)2D, calcitriol)
• Ergocalciferol (vitamin D2)

Correct Answer: 1,25-dihydroxyvitamin D (1,25(OH)2D, calcitriol)

Q8. Which renal enzyme catalyzes formation of calcitriol from 25-hydroxyvitamin D?

• CYP27B1 (1-alpha-hydroxylase)
• CYP24A1 (24-hydroxylase)
• CYP2R1 (25-hydroxylase)
• CYP11A1

Correct Answer: CYP27B1 (1-alpha-hydroxylase)

Q9. Parathyroid hormone (PTH) affects renal vitamin D metabolism by:

• Inhibiting CYP27B1 activity
• Stimulating CYP27B1 activity
• Stimulating CYP24A1 activity
• Blocking vitamin D binding protein

Correct Answer: Stimulating CYP27B1 activity

Q10. Which factor decreases renal 1-alpha-hydroxylase activity and lowers calcitriol production?

• Low phosphate levels
• Parathyroid hormone (PTH)
• Fibroblast growth factor 23 (FGF23)
• Hypocalcemia

Correct Answer: Fibroblast growth factor 23 (FGF23)

Q11. The major circulating indicator of vitamin D status measured clinically is:

• Cholecalciferol (vitamin D3)
• 1,25-dihydroxyvitamin D (calcitriol)
• 25-hydroxyvitamin D (25(OH)D, calcidiol)
• 7-dehydrocholesterol

Correct Answer: 25-hydroxyvitamin D (25(OH)D, calcidiol)

Q12. Which assay method is considered gold standard for measuring vitamin D metabolites due to specificity?

• Radioimmunoassay (RIA)
• ELISA
• LC-MS/MS (liquid chromatography-tandem mass spectrometry)
• Colorimetric assay

Correct Answer: LC-MS/MS (liquid chromatography-tandem mass spectrometry)

Q13. Which cytochrome P450 enzyme is responsible for catabolic 24-hydroxylation of vitamin D metabolites?

• CYP24A1
• CYP27A1
• CYP2R1
• CYP27B1

Correct Answer: CYP24A1

Q14. Ergocalciferol (vitamin D2) differs from cholecalciferol (vitamin D3) primarily by:

• Presence of an extra methyl group only
• Different side-chain double bond and methylation
• Different ability to bind DBP (no structural difference)
• Location of hydroxylation in liver

Correct Answer: Different side-chain double bond and methylation

Q15. Which statement about vitamin D3 versus D2 is correct?

• Vitamin D2 has a longer half-life and greater potency than D3
• Vitamin D3 is generally more potent and raises serum 25(OH)D more effectively
• Vitamin D2 cannot be converted to 25(OH)D
• Both are identical and interchangeable at molecular level

Correct Answer: Vitamin D3 is generally more potent and raises serum 25(OH)D more effectively

Q16. Excessive vitamin D intake leading to hypercalcemia is largely due to increases in which form?

• Cholecalciferol (vitamin D3)
• 25-hydroxyvitamin D
• 1,25-dihydroxyvitamin D (calcitriol)
• 7-dehydrocholesterol

Correct Answer: 1,25-dihydroxyvitamin D (calcitriol)

Q17. The intracellular receptor that mediates most genomic effects of calcitriol is:

• Estrogen receptor
• Vitamin D receptor (VDR)
• Thyroid hormone receptor
• Glucocorticoid receptor

Correct Answer: Vitamin D receptor (VDR)

Q18. Upon activation, VDR commonly heterodimerizes with which partner to regulate gene transcription?

• RXR (retinoid X receptor)
• GR (glucocorticoid receptor)
• NF-κB
• PPAR-gamma

Correct Answer: RXR (retinoid X receptor)

Q19. Which effect is a primary action of calcitriol on the intestine?

• Decrease passive calcium diffusion
• Increase active calcium absorption by upregulating TRPV6 and calbindin
• Inhibit phosphate transporters
• Reduce vitamin D binding protein synthesis

Correct Answer: Increase active calcium absorption by upregulating TRPV6 and calbindin

Q20. Older adults synthesize less vitamin D in skin mainly because of:

• Reduced sun exposure only
• Lower levels of 7-dehydrocholesterol in the epidermis
• Increased melanin production
• Higher vitamin D binding protein levels

Correct Answer: Lower levels of 7-dehydrocholesterol in the epidermis

Q21. Which drug class is known to increase vitamin D catabolism via induction of hepatic P450 enzymes?

• Beta-blockers
• Anticonvulsants like phenytoin and phenobarbital
• ACE inhibitors
• SSRIs

Correct Answer: Anticonvulsants like phenytoin and phenobarbital

Q22. A patient with granulomatous disease (e.g., sarcoidosis) may develop hypercalcemia due to:

• Excessive renal inactivation of vitamin D
• Macrophage-mediated extrarenal 1-alpha-hydroxylation producing calcitriol
• Decreased intestinal absorption of calcium
• Reduced PTH secretion with low calcitriol

Correct Answer: Macrophage-mediated extrarenal 1-alpha-hydroxylation producing calcitriol

Q23. The unit conversion between ng/mL and nmol/L for 25(OH)D is:

• 1 ng/mL = 1 nmol/L
• 1 ng/mL = 2.5 nmol/L
• 1 ng/mL = 0.5 nmol/L
• 1 ng/mL = 10 nmol/L

Correct Answer: 1 ng/mL = 2.5 nmol/L

Q24. Genetic deficiency of CYP27B1 manifests clinically as which type of rickets?

• Vitamin D–dependent rickets type I
• Vitamin D–dependent rickets type II
• Hypophosphatasia
• Vitamin D resistant rickets due to renal phosphate wasting

Correct Answer: Vitamin D–dependent rickets type I

Q25. Vitamin D receptor (VDR) mutations causing end-organ resistance to calcitriol are called:

• Vitamin D–dependent rickets type I
• Vitamin D–dependent rickets type II
• Familial hypocalciuric hypercalcemia
• Osteogenesis imperfecta

Correct Answer: Vitamin D–dependent rickets type II

Q26. Which tissue can perform 1-alpha-hydroxylation of 25(OH)D besides the kidney?

• Heart muscle
• Macrophages and placenta
• Pancreas
• Hair follicles

Correct Answer: Macrophages and placenta

Q27. The main physiological trigger for increased renal 1-alpha-hydroxylase activity is:

• Hypercalcemia
• Low PTH levels
• Hypocalcemia and elevated PTH
• High FGF23 levels

Correct Answer: Hypocalcemia and elevated PTH

Q28. Which clinical finding is most characteristic of vitamin D deficiency in adults?

• Hypercalcemia with bone pain
• Osteomalacia with bone pain and muscle weakness
• Increased bone density
• Hyperphosphatemia without symptoms

Correct Answer: Osteomalacia with bone pain and muscle weakness

Q29. Sunscreen with high SPF reduces vitamin D synthesis mainly by blocking:

• Infrared radiation
• UVA only
• UVB radiation
• Visible light

Correct Answer: UVB radiation

Q30. Which blood level cutoff of 25(OH)D is commonly considered deficient by many guidelines (< ... )?

• < 5 ng/mL
• < 12 ng/mL (30 nmol/L)
• < 50 ng/mL
• < 100 ng/mL

Correct Answer: < 12 ng/mL (30 nmol/L)

Q31. The half-life of 25-hydroxyvitamin D in circulation is approximately:

• 4–6 hours
• 24–48 hours
• 2–3 weeks
• 6 months

Correct Answer: 2–3 weeks

Q32. Vitamin D increases serum calcium by which combined mechanisms?

• Decrease intestinal calcium absorption and bone resorption
• Increase intestinal absorption and increase bone resorption
• Reduce PTH and inhibit intestinal calcium transport
• Stimulate renal calcium excretion only

Correct Answer: Increase intestinal absorption and increase bone resorption

Q33. Which enzyme defect leads to accumulation of vitamin D metabolites and risk of hypervitaminosis D due to impaired catabolism?

• CYP24A1 mutation
• CYP2R1 mutation
• CYP27B1 mutation
• CYP3A4 deficiency

Correct Answer: CYP24A1 mutation

Q34. Which of the following factors increases cutaneous vitamin D3 production?

• High latitude and winter season
• Use of sunscreen SPF 50
• Low melanin content (fair skin)
• Age over 70 years

Correct Answer: Low melanin content (fair skin)

Q35. Vitamin D binding protein (DBP) polymorphisms mainly influence:

• Renal 1-alpha-hydroxylase activity
• Serum total 25(OH)D concentrations and free fraction
• Skin synthesis of previtamin D3
• Intestinal absorption of dietary vitamin D

Correct Answer: Serum total 25(OH)D concentrations and free fraction

Q36. Non-genomic rapid actions of vitamin D are mediated by:

• Slow nuclear transcription only
• Membrane-associated receptors and signaling cascades
• Direct calcium binding in plasma
• Inhibition of cytochrome P450 enzymes

Correct Answer: Membrane-associated receptors and signaling cascades

Q37. Which medication commonly used in tuberculosis enhances vitamin D activation by increasing expression of 1-alpha-hydroxylase in macrophages and may cause hypercalcemia?

• Isoniazid
• Rifampicin
• Pyrazinamide
• Ethambutol

Correct Answer: Rifampicin

Q38. In pharmacotherapy, the preferred supplement for replacement of severe deficiency is often:

• High-dose oral cholecalciferol (vitamin D3)
• Topical vitamin D analogs
• Intravenous calcidiol
• Inhaled vitamin D

Correct Answer: High-dose oral cholecalciferol (vitamin D3)

Q39. Which laboratory value would you expect in a patient with 1-alpha-hydroxylase deficiency (vitamin D‑dependent rickets type I)?

• Low 25(OH)D, high 1,25(OH)2D
• Normal 25(OH)D, low 1,25(OH)2D
• High 25(OH)D, high 1,25(OH)2D
• Low PTH with hypercalcemia

Correct Answer: Normal 25(OH)D, low 1,25(OH)2D

Q40. Which transport route helps distribute vitamin D produced in the skin to the liver?

• Portal vein direct transport
• Lymphatic system via chylomicrons
• Binding to DBP and systemic circulation
• Exocytosis by keratinocytes directly to kidney

Correct Answer: Binding to DBP and systemic circulation

Q41. Which clinical condition decreases cutaneous synthesis of vitamin D the most?

• Use of broad-spectrum sunscreen with high SPF
• Regular moderate sun exposure
• Daily intake of fortified milk
• Topical application of vitamin D cream

Correct Answer: Use of broad-spectrum sunscreen with high SPF

Q42. Which of the following is a direct pharmacological use of calcitriol?

• First-line therapy for acute hypocalcemia in all patients
• Treatment of secondary hyperparathyroidism in chronic kidney disease
• Primary prevention of skin cancer
• Treatment of vitamin B12 deficiency

Correct Answer: Treatment of secondary hyperparathyroidism in chronic kidney disease

Q43. The main reason 1,25(OH)2D levels are not used to determine vitamin D nutritional status is:

• They are too stable and do not reflect current changes
• 1,25(OH)2D has a short half-life and is regulated by PTH and calcium, not stores
• Assays for 1,25(OH)2D are universally unreliable
• 1,25(OH)2D is not biologically active

Correct Answer: 1,25(OH)2D has a short half-life and is regulated by PTH and calcium, not stores

Q44. Which population factor most reduces cutaneous vitamin D production?

• Living near equator
• Dark skin pigmentation
• Outdoor occupations without clothing
• Young age

Correct Answer: Dark skin pigmentation

Q45. Which dietary form of vitamin D is plant-derived and often used in fortified foods and supplements?

• Cholecalciferol (vitamin D3)
• Calcitriol
• Ergocalciferol (vitamin D2)
• 25-hydroxyvitamin D

Correct Answer: Ergocalciferol (vitamin D2)

Q46. Which statement about storage of vitamin D in the body is correct?

• Vitamin D is water-soluble and stored in plasma
• Vitamin D is fat-soluble and stored in adipose tissue
• Vitamin D cannot be stored and must be synthesized daily
• Vitamin D is stored exclusively in bone matrix

Correct Answer: Vitamin D is fat-soluble and stored in adipose tissue

Q47. In drug interactions, which oral medication can reduce vitamin D activation by inducing hepatic enzymes?

• Simvastatin
• Rifampicin
• Metformin
• Levothyroxine

Correct Answer: Rifampicin

Q48. An important biochemical action of calcitriol on bone is to:

• Directly mineralize osteoid without affecting osteoclasts
• Decrease RANKL expression on osteoblasts
• Increase RANKL expression promoting osteoclast differentiation and bone resorption
• Block parathyroid hormone release completely

Correct Answer: Increase RANKL expression promoting osteoclast differentiation and bone resorption

Q49. Which food source is naturally richest in cholecalciferol (vitamin D3)?

• Beef liver
• Fatty fish like salmon and mackerel
• Oranges
• Whole grains

Correct Answer: Fatty fish like salmon and mackerel

Q50. For B.Pharm students, which enzyme target would be most relevant when designing a drug to reduce active vitamin D levels in hypervitaminosis D?

• Activator of CYP27B1
• Inhibitor of CYP24A1
• Activator of CYP24A1 (24-hydroxylase)
• Inhibitor of vitamin D binding protein

Correct Answer: Activator of CYP24A1 (24-hydroxylase)

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

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