Vitamin D

Question 1

What is 25 Hydroxyvitamin D, where is it found and what is it used as?

Answer 1

Inactive form of vitamin D
Found in excess in the liver
Used as a marker of nutritional status

Question 2

What is 1,25 Dihydroxyvitamin D? Where is it metabolised and describe its mechanism of action

Answer 2

Active form of vitamin D
Metabolised in the kidney

Binds to a vitamin D receptor and becomes a transcription factor that modulates gene expression of transport proteins which are involved in calcium absorption from the gut.

Question 3

List 3 other roles of vitamin D aside from acting as a transcription factor

Answer 3

Promotes calcium absorption from the intestine
Increases osteoclast numbers casing bone resorption
Maintains calcium homeostasis via PTH for bone formation

Question 4

What is osteomalacia caused by and what effect does that have on bones?

Answer 4

Vitamin D deficiency

Impaired mineralisation of bones

Question 5

List primary/nutritional causes of vitamin D deficiency

Answer 5

Asian immigrants: chapattis, lack of sunlights exposure
Elderly housebound
Bizarre diets

Low dietary intake

Question 6

List secondary causes of vitamin D deficiency

Answer 6

Vitamin D deficiency:

• • partial gastrectomy
• • small intestine malabsorption
• • Pancreatic disease

Chronic renal failure
Anticonvulsants
Hypophosphatemia