Vitamin A

Question 1

What was the first vitamin to be discovered?

Answer 1

Vitamin A

Question 2

What are the active forms (vitamers) of vitamin A?

Answer 2

• Retinol
• Retinal
• Retinoic acid

Question 3

What happens to retinol depending on the body’s needs?

Answer 3

It can be oxidised to retinal or retinoic acid, or remain as retinol and be stored in the liver.

Question 4

What is pro-vitamin A and where is it converted into active vitamin A?

Answer 4

Pro-vitamin A is converted into retinol in the small intestinal epithelium and liver.

Question 5

What are examples of pro-vitamin A?

Answer 5

• Carotenes
• Carotenoids

Question 6

What are the most active pro-vitamin carotenes?

Answer 6

• α-carotene
• β-carotene
• γ-carotene
• Cryptoxanthin

Question 7

Where is pre-formed vitamin A found?

Answer 7

Only in animal foods.

Question 8

What are rich food sources of pro-vitamin A?

Answer 8

• Dark green vegetables
• Yellow/orange vegetables
• Fruits (e.g., carrots, squash, mango, spinach, sweet potatoes)

Question 9

What is the absorption range of carotenoids in the small intestine?

Answer 9

5% to 60%

Question 10

What dietary component is necessary for carotenoid absorption?

Answer 10

Healthy fats

Question 11

What cooking method can increase the bioavailability of carotenoids?

Answer 11

Slightly steaming the foods.

Question 12

What gene encodes the enzyme that converts carotenoids to retinal?

Answer 12

BCO1 gene

Question 13

What can reduce carotene conversion?

Answer 13

• Hyperlipidaemia
• Liver disorders
• Diabetes
• Hypothyroidism

Question 14

What can excessive intake of carotenoids lead to?

Answer 14

A non-dangerous yellowing of the skin.

Question 15

What percentage of dietary retinol is absorbed?

Answer 15

70–90%

Question 16

What is the maximum supplemental dosage of pre-formed vitamin A for adults?

Answer 16

3000 mcg

Question 17

What is the conversion of vitamin A activity expressed as?

Answer 17

mcg of retinol activity equivalents (RAE)

Question 18

What does 1 RAE equal in terms of retinol and beta-carotene?

Answer 18

• 1 mcg of retinol
• 12 mcg of beta-carotene
• 24 mcg of alpha-carotene or beta-cryptoxanthin

Question 19

What is required for the synthesis of rhodopsin?

Answer 19

Vitamin A

Question 20

What are some therapeutic uses of vitamin A related to vision?

Answer 20

• Photosensitivity
• Visual loss
• Night-blindness
• Senile cataracts

Question 21

How does vitamin A support immunity?

Answer 21

Enhances T-cell proliferation and supports skin and mucous membrane barrier.

Question 22

What role does vitamin A play in gene expression?

Answer 22

Regulates the expression of over 500 genes affecting cell functioning.

Question 23

What are some therapeutic uses of vitamin A related to gene expression?

Answer 23

• Acne
• Anaemia
• Cervical dysplasia
• Hair loss in women
• Fracture repair

Question 24

What reproductive functions does vitamin A support?

Answer 24

Spermatogenesis and egg development.

Question 25

What are the antioxidant properties of vitamin A?

Answer 25

Both pre-formed and provitamin A have antioxidant properties.

Question 26

What are some signs and symptoms of vitamin A deficiency?

Answer 26

* Vision impairment at night * Hyperkeratosis of skin * Reduced skin integrity * Poor bone growth * Lowered immunity

Question 27

What can accelerate the breakdown of liver-stored retinol?

Answer 27

Alcoholism

Question 28

What can lead to vitamin A toxicity?

Answer 28

Long-term intake of 5–10 times the recommended nutrient intake.

Question 29

What are potential consequences of vitamin A toxicity?

Answer 29

* Birth defects * Increased bone fractures * Liver disease * Hyperlipidaemia

Question 30

What should be avoided when taking warfarin?

Answer 30

Vitamin A supplementation