Vitamin A

Vitamin A (retinol, retinal, retinoic acid) is a group of nutritionally unsaturated hydrocarbons, which include retinol, retinal, retinoic acid and several pro-vitamin A carotenoids. It is involved in the formation and maintenance of healthy skin, hair and mucous membranes. Vitamin A helps humans to see in dim light and is necessary for proper bone growth, tooth development and reproduction.

It assists the immune system, and its antioxidant properties protect against pollution, cancer formation and various diseases. It also assists with the sense of taste as well as helping the digestive and urinary tract and many believe that it helps slow aging. It is also required for development and maintenance of the epithelial cells, in the mucus membranes and the skin and is important in the storage of fat and the synthesis of protein and glycogen. Vitamin A and carotenoids are vital for eye health. Adequate levels of zinc are needed to transport vitamin A to the retina.

Two forms of vitamin A are available in the human diet:

1. Preformed vitamin A (retinol and its esterified form, retinyl ester)
2. Provitamin A (carotenoids)

Preformed vitamin A is found in foods from animal sources, including dairy products, fish, and meat (especially liver). The microbe in the guts metabolise dietary vitamin A and convert it into its active form, retinoic acid (RA),

By far the most important provitamin A carotenoid is beta-carotene; other pro-vitamin A carotenoids are alpha-carotene and beta-cryptoxanthin.

The body converts these plant pigments into vitamin A. Both pro-vitamin A and preformed vitamin A must be metabolised intracellularly to retinal and retinoic acid, the active forms of vitamin A, to support the vitamin’s important biological functions.

Other carotenoids found in food, such as lycopene, lutein and zeaxanthin, are not converted into vitamin A.

Vitamin A helps to move iron from storage in the body, without adequate amounts of vitamin A the body cannot regulate iron properly leading to an iron deficiency.

The body stores vitamin A as it is fat-soluble., mainly in fatty tissues, and mostly in the liver. This allows the body to utilise it over time, rather than needing a daily dose.

Deficiency of vitamin A

Deficiency can cause depression. It may also lead to eye problems with dryness of the conjunctiva and cornea, night blindness as well as poor growth. Dry itchy eyes that tire easily are normally a warning of too little vitamin A. If the deficiency becomes severe, the cornea can ulcerate, and permanent blindness can follow.

What are the signs of vitamin A deficiency?

• Abscesses forming in the ears
• Dry eyes
• Fatigue
• Frequent colds and infections
• Hair loss
• Infertility
• Insomnia
• Night blindness
• Respiratory infections
• Sinusitis
• Skin disorders (acne, boils and a bumpy skin)
• Weight loss

The hair and scalp can also become dry with vitamin A deficiency, especially if protein is also lacking. Prolonged deficiency leads to the rapid loss of vitamin C.

NOTE: A common carcinogen found in cigarettes called benzopyrene can cause vitamin A deficiency.

Vitamin A toxicity

High levels of vitamin A consumption can cause birth defects so the foods below are best limited during pregnancy and supplements containing vitamin A should be avoided completely. Vitamin A taken in excessive doses may cause liver damage and weaken bones. Too much vitamin A interferes with vitamin D in the body.

Natural sources of preformed vitamin A in alphabetical order

Highest sources of vitamin A in micrograms per 100 grams

• Pork liver 39 mg
• Cod liver oil 30 mg
• Calves liver 25,2 mg
• Eggs 15 mg
• Chicken liver, 10,5 mg
• Trout 10 mg
• Oysters 9.8 mg
• Cheese (goats) 8.2 mg
• Milk (whole) 7.8 mg
• Beef liver, lambs liver 7,7 mg
• Cheese (cheddar) 7.4 mg
• Turkey giblets 3,1 mg
• Eel, yellow, raw 1,2 mg

Carotenoids

Consuming foods rich in carotenoids helps the body to produce vitamin A. Supplements should be avoided as they have been known to worsen lung disorders and even cause cancer in smokers.

Most of the carotenoids in fruits and vegetables are in the skin, so it is wise best not to peel fruits and vegetables when possible. Lightly steaming some foods, such as carrots, spinach and tomatoes can actually improve the body’s ability to absorb them.

NOTE: Carotenoids are fat-soluble which means they must be consumed with a little oil in order for the body to absorb them. Add a tablespoon of a cold-pressed oil such as coconut, fish, nut, olive, rapeseed or other nut or seed oils.

Highest sources of alpha-carotene in micrograms per 100 grams

Highest sources of beta-carotene in micrograms per 100 grams

NOTE: One µg is one microgram.

NOTE: About 45% people carry a genetic mutation that significantly reduces their ability to convert carotenoids into vitamin A.

Related subjects

• A-Z of Natural Foods and Remedies
• A-Z of Nutrients
• Allergies
• Alpha-carotene
• Beta-carotene
• Bone and joint disorders
• Cancer
• Ear disorders
• Eye disorders
• Hair and nail disorders (poor condition and hair loss)
• Heart disorders
• Immune system disorders
• Infertility
• Insomnia
• Intestinal disorders
• Respiratory disorders
• Skin disorders (acne, boils)
• Urinary tract infection

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