Vitamin A

Question 1

Vitamin A

Answer 1

• Vitamin A was the first vitamin to be discovered (hence ‘A’).
• The active forms (vitamers) which execute the functions of vitamin A are: Retinol, Retinal and Retinoic Acid
• Depending upon what the body requires, retinol will be oxidised to the different forms (retinol ->, retinal -> retinoic acid) acid). If the body
doesn’t need it, it will remain as retinol and be stored in the liver.

Question 2

Vitamin A: Forms

Answer 2

Pro-vitamin A

Pre-formed vitamin A

Question 3

Pro-vitamin A

Answer 3

Converted into the active (usable) form of vitamin A (retinol) in the small intestinal epithelium and liver.
- Carotenes (or carotenoids) are examples of pro vitamin A. The most active pro vitamin carotenes are: α –(alpha), β –(beta) and
γ –(gamma) carotenes and cryptoxanthin
- Found in non-animal foods

Question 4

Pre-formed vitamin A

Answer 4

This is active vitamin A the body can use as it is.

- Only found in animal foods.

Question 5

Vitamin A: Food Sources

Answer 5

Pro-vitamin A are produced by plants, algae, fungi and bacteria. Rich Food sources: Dark green, yellow/orange vegetables and fruit, e.g. carrots, squash, mango, spinach, sweet potatoes

Pre-formed vitamin A is only found in animal foods e.g. liver, fish, liver oils, egg yolk, mackerel, salmon

Question 6

Pro-vitamin A Absorption

Answer 6

• Dietary carotenes are converted to vitamin A only as needed, so do not have toxicity concerns.
• The absorption of carotenoids in the small intestine varies between 5% and 60%.
• Ensure that there are adequate healthy fats in the diet as carotenoids are fat soluble. Drizzle with coconut oil or olive oil to optimise absorption.
• Another way to increase the bioavailability of carotenoids is to cook (slightly steam) these foods, e.g. carrots. This cooking method is
thought to most effectively liberate carotenoids from cells.

Question 7

Carotenoids and Conversion

Answer 7

• The enzyme which converts carotenoids to retinol (in the intestinal epithelium and liver) is encoded by the BCO1 gene. This enzyme activity is subject to much genetic variation.
• Carotene conversion is reduced by: hyperlipidaemia, liver disorders, diabetes and hypothyroidism
• Excessive intake of carotenoids can lead to a non dangerous yellowing on the skin . However, yellowing of the skin might also be associated with disorders of the liver, gallbladder, etc.
• A sallow yellow complexion (i.e. pale or pasty), especially in the face, can indicate a Spleen Qi deficiency . In TCM, this refers to ‘weakness’ in digestion function.

Question 8

Pre-formed Vitamin A abosorption

Answer 8

About 70-90% of dietary retinol is absorbed this is a key reason that animal food sources of vitamin A can lead to vitamin A toxicity (liver particularly).

Question 9

Pre-formed Vitamin A Dosage

Answer 9

• Supplemental Range: Adults maximum 3000mcg pre-formed A. Higher doses are appropriate in some situations but should only be used short term.
• It is recommended to avoid isolated beta carotene supplementation, as it was shown to worsen the progression of lung cancer patients in a research study ( recall that antioxidants do not work in isolation)
• Carotenes (provitamin A) don’t have the same vitamin A activity as pre-formed vitamin A. The amounts of vitamin A are expressed as mcg of Retinol Activity Equivalents (RAE).

Question 10

Vitamin A Effects

Answer 10

Vison and Eye Health
Immunity
Gene Expression and cell differentiation
Reproduction
Anti-oxidant properties

Question 11

Vitamin A: Vision & Eye Health - Functions

Answer 11

• Required for rhodopsin the light sensitive protein involved in converting light into an electrical signal that goes into the brain’s visual cortex, giving the message of sight.
• Also necessary for corneal health.

Question 12

Vitamin A: Vision and Eye Health - Therapeutic uses

Answer 12

• Photosensitivity
• Visual loss
• Night blindness
• Senile cataracts

Question 13

Vitamin A: Immunity - Functions

Answer 13

• Enhances T-cell proliferation and Interleukin 2 secretion.

* Supports first line of immune defence (skin and mucous membrane barrier)

Question 14

Vitamin A: Immunity - Therapeutic Uses

Answer 14

• Recurrent infections, e.g. respiratory tract infections

Question 15

Vitamin A: Gene Expression - Functions

Answer 15

• Control of cell differentiation and turnover. Regulating the expression of over 500 genes, affecting the synthesis of proteins that regulate cell functioning.
• Key as a preventive measure to support healthy gene expression
• Synthesis of glycoproteins which support normal development of bones, teeth and skin.

Question 16

Vitamin A: Gene Expression - Therapeutic Uses

Answer 16

• Acne
• Anaemia
• Cervical dysplasia
• Hair loss in women
• Fracture repair
• Lichen planus
• Osteoarthritis
• GIT ulceration
• Vaginitis
• Periodontal disease

Question 17

Vitamin A: Reproduction - Functions

Answer 17

• Reproductive & embryonic health.
• Required for spermatogenesis in men.
• Required for egg (ovum) development and implantation.

Question 18

Vitamin A: Reproduction - Therapeutic Uses

Answer 18

• Infertility (male & female)

* Fibrocystic breast disease

Question 19

Vitamin A: Anti-Oxidant Properties - Functions

Answer 19

• Pre-formed and pro-vitamin A have antioxidant properties.
• The foods rich in carotenoids are also rich in other antioxidants, again highlighting that they don’t work in isolation.

Question 20

Vitamin A: Anti-oxidant properties - Therapeutic Uses

Answer 20

• Used in various therapies, including carrot juicing for cancer (Gerson
therapy).
• Disease prevention

Question 21

Vitamin A Deficiency Signs and Symptoms

Answer 21

• Vision impairment at night is an early sign: Loss of sensitivity to green light, unable to adapt to dim light and night blindness. Prolonged deficiency can lead to blindness.
• Hyperkeratosis of skin of upper arms.
• Reduced skin integrity rough dry skin, acne, eczema, poor wound healing. Dry hair.
• Poor bone growth / development.
• Poor sense of taste and smell .
• Lowered immunity ( recurrent infections)

Question 22

Vitamin A - Factors Affecting Individual Requirements

Answer 22

• Diabetes mellitus, thyroid & liver disease ––↓carotene
• Alcoholism: accelerates the breakdown of liver stored retinol; absorption and carotene conversion is reduced. Increased vitamin A toxicity potential; do not supplement with preformed A.
• Poor gut health (lack of absorption in small intestine) and conditions that affect fat absorption, e.g. cystic fibrosis, statins, etc.
• Zinc deficiency and/or protein malnutrition: zinc and protein are required to make Retinol Binding Protein (RBP). RBP moves vitamin A from liver storage to tissues for utilisation. Without zinc, vitamin A is trapped. So optimise intake of zinc rich foods.

Question 23

Vitamin A Toxicity

Answer 23

Vitamin A Toxicity: long term and regular intake (roughly 5-10 times the recommended nutrient intake over many months):
• Can negatively affect gene regulation during embryological development leading to birth defects (e.g. cleft lip)
• May increase osteoclast activity and lead to bone fractures
• Can damage hepatocyte cell membranes (causing liver disease
• Can lead to hyperlipidaemia, amenorrhoea and anorexia.
• Can cause dry, red and scaling skin .

Question 24

Vitamin A Drug Interactions

Answer 24

Be wary of vitamin A supplementation with those taking warfarin,
as it decreases vitamin K absorption (increasing bleeding risk).

Question 25

The gene that encodes carotenoid conversion

Answer 25

BCO1

Question 26

RAE and Conversion

Answer 26

• 1 RAE = 1 mcg of retinol = 12 mcg of beta carotene = 24 mcg of alpha carotene or beta cryptoxanthin from dietary sources.
• Supplements conversion is: 2mcg beta carotene = 1mcg retinol.
• Vitamin A content using international units (IU) is being phased out of supplements by January 2021. 1 IU retinol = 0.3 mcg RAE.