Lecture 9: Micronutrients

Question 1

what are the essential vitamins

Answer 1

• A
• D
• E
• K
• vitamin C
• thiamine: B1
• riboflavin: B2
• niacin B3
• pantothenic acid B5
• vitamin B6
• folate B9
• vitamin B12

Question 2

what are micronutrient deficiencies seen in the population

Answer 2

• vitamin D
• riboflavin B2
• iron deficiency in women

Question 3

what micronutrient deficiencies are associated with alcohol liver disease

Answer 3

• thiamine B1

- vitamin D

Question 4

what micronutrient deficiencies are associated with IBS

Answer 4

• iron
• B1
• B6
• B12
• vitamin D
• vitamin K
• folic acid

Question 5

what micronutrient deficiences are associated with obesity

Answer 5

• vitamin D
• copper
• zinc

Question 6

where is vitamin C absorbed

Answer 6

• buccal mucosa
• stomach
• small intestine

Question 7

what is vitamin C’s mechanism of absorption

Answer 7

• buccal: passive diffusion

- GI: rapidly through carrier mediated transport system

Question 8

what is vitamin B1’s mechanism of absorption

Answer 8

• at low concentrations, by active sodium dependent processes
• at high concentrations, by passive diffusion

Question 9

what does vitamin B1 deficiency cause

Answer 9

Wernicke-Korsakoff syndrome

Question 10

what is vitamin B2’s mechanism of absorption

Answer 10

• released from proteins by proteolytic enzymes

- then hydrolysed by brush border enzymes

Question 11

what are dietary sources of B12

Answer 11

• is synthesised by microorganisms
• then concentrated through food chains
• on plants, contamination by soil bacteria

Question 12

how is vitamin B12 absorbed

Answer 12

1. B12 binds to R factor in presence of HCl
2. R complex degraded in jejunum and B12 binds to Intrinsic Factor (IF)
3. B12-IF complex binds to receptors at distal ileum
4. B12 is absorbed into plasma in presence of calcium

Question 13

what does vitamin B12 deficiency cause

Answer 13

pernicious anaemia

Question 14

what are dietary sources of vitamin A

Answer 14

• retinol is in long fatty acid chains in animals

- precursor carotenoids in red/orange plants

Question 15

what is vitamin A’s mechanism of absorption

Answer 15

• retinol hydrolysed by pepsin in stomach and proteolytic enzymes in small intestine
• carotenes packaged into micelles, absorbed through membrane and converted to retinol

Question 16

what are dietary sources of vitamin D

Answer 16

• animal foods: D2

- synthesised in body via UV light: D3

Question 17

what is vitamin D’s mechanism of absorption

Answer 17

• absorbed form micelle by passive diffusion
• liver 25-hydroxylase enzymes convert D2 and D3 to 25-hydroxy-vitamin D
• this is then converted to the active form 1,25-dihydroxyvitamin D by the kidney and other tissues

Question 18

what is calcium’s mechanism of absorption

Answer 18

• 20-30% is absorbed in acid medium
• when intake is low and requirement is high, via vitamin D dependent transport system in duodenum
• when intake is high, via passive processes in jejunum

Question 19

what are dietary sources of iron

Answer 19

• haem iron in animal products

- non-haem in plant foods

Question 20

what is iron’s mechanism of absorption

Answer 20

• very difficult to absorb as it is associated with proteins
• haem is easier to absorb than non-haem
• haem iron absorbed as intact porphyrin complex
• non-haem is oxidised from ferric to ferrous form
• this process is aided by vitamin C