Vitamin A

Introduction

Vitamin A is the name of a group of fat-soluble retinoids, including retinol, retinal, retinoic acid, and retinyl esters.

Vitamin A is involved in immune function, vision, reproduction, and cellular communication.

Eye sight

Vitamin A is critical for vision as an essential component of rhodopsin, a protein that absorbs light in the retinal receptors, and because it supports the normal differentiation and functioning of the conjunctival membranes and cornea.

Cell growth

Vitamin A also supports cell growth and differentiation, playing a critical role in the normal formation and maintenance of the heart, lungs, kidneys, and other organs.

Forms of vitamin A

There are essentially 3 forms of vitamin A: Retinols, Beta carotenes, Carotenoids. Retinol It is also known as preformed vitamin A, is the

most active form and is mostly found in animal sources of food.

Beta carotene

Beta carotene, also known as pro vitamin A, is the plant source of retinol from which mammals make two-thirds of their vitamin A.

Carotenoids, the largest group of the 3, contain multiple conjugated double bonds and exist in a free alcohol or in a fatty acyl-ester form.

Sources of Vitamin A

Animal source of Vit A

Vitamin A comes from animal sources such as eggs, meat and dairy products.

Vegetables source of Vit A

Beta carotene a precursor of Vit. A comes from Fruits and leafy vegetables.

These are not as useful for obtaining vitamin A as was thought; the IUs these foods contain are much less than the same number of IUs of fat-dissolved oils and (to some extent) supplements.

Vegetarians and Night blindness

This is important for vegetarians, as night blindness is prevalent in countries where little meat or vitamin A-fortified foods are available.

Vitamin A Functions

Vitamin A plays a role in : Vision Gene transcription Immune function Embryonic development and reproduction Bone metabolism Haematopoiesis Skin and cellular health Antioxidant activity

Vitamin A deficiency

It is a public health problem in more than half of all countries, especially in Africa and South-East Asia, hitting hardest young children and pregnant women in low-income countries.

Cont…

Between 100 and 140 million children are vitamin A deficient; 250,000-500,000 of these children become blind every year and half of these die within 12 months of losing their sight.

In pregnant women, vitamin A deficiency occurs especially in the last trimester (demand by fetus and mother is highest).

For children

The lack of vitamin A causes severe visual impairment and blindness, and significantly increases the risk of :

severe illness, and even death, from such common childhood infections as

diarrhoeal disease and measles.

For pregnant women

In high-risk areas, vitamin A deficiency occurs especially during the last trimester when demand by both the unborn child and the mother is highest.

The mother’s deficiency is demonstrated by the high prevalence of night blindness during this period.

Recommended Daily Allowance

Recommended Daily Allowance (RDA) for vitamin A is;

700 RE per day for women 900 RE per day for men. ( 1mcg of Retinol= 1mcg of Retinol) ( 1mcg of beta carotene= 0.167mcg of

Retinol)

How to prepare foods to retain vitamin A.

Vitamin A can be lost from foods during preparation, cooking, or storage. To prevent loss of vitamin A:

Use raw fruits and vegetables whenever possible.

Keep vegetables (except sweet potatoes and winter squash) and fruits covered and refrigerated during storage.

Steam vegetables and meats instead of frying. Some of the vitamin A is lost in the fat during frying.

Impacts

Animals and humans deficient in vitamin A grow poorly, suffered more persistent or severe infections, ocular problems termed "xerophthalmia" or

"dry eye".

Primary vitamin A deficiency

This is caused by prolonged dietary deficiency, particularly where rice is the staple food (doesn't contain carotene).

Vitamin A deficiency occurs with protein-energy malnutrition (marasmus or kwashiorkor) mainly because of dietary deficiency (but vitamin A storage and transport are also impaired).

Secondary vitamin A deficiency

This occurs where there are problems in converting carotene to vitamin A, or reduced absorption, storage, or transport of vitamin A.

This occurs in coeliac disease, tropical sprue, giardiasis, cystic fibrosis, other pancreatic disease, cirrhosis, duodenal bypass surgery, and bile duct obstruction.

Presentation

Mild forms of vitamin A deficiency may cause no symptoms. However, there may still be an increased risk of developing respiratory infections and gastroenteritis, and delayed growth and bone development.

Cont…

There is also a risk of infertility secondary to impaired spermatogenesis, and an increased risk of miscarriage.

Fatigue may present as a consequence of vitamin A deficiency anaemia.

Ocular manifestation

Night blindness Poor adaptation to darkness -. Keratomalacia (thinning and ultimately

ulceration of the cornea - colliquative necrosis). Xerophthalmia Conjunctival dryness, corneal

dryness,.

Cont...

Bitot's spots (areas of abnormal squamous cell proliferation and keratinisation of the conjunctiva, causing oval, triangular or irregular foamy patches on the white of the eye).

Corneal perforation. Blindness due to structural damage to the

retina.

Extra ocular

Skin and hair: Dry skin, dry hair, pruritis. Broken fingernails. Follicular hyperkeratosis secondary to

blockage of hair follicles, with plugs of keratin.

Less specific changes

Other less specific changes include: Keratinisation of mucous membranes. Increased susceptibility to infection (due to

impairment of the humoral and cell-mediated immunity).

Skin changes (follicular hyperkeratosis) are also common.

Prevention

Liver, beef, chicken, eggs, whole milk, fortified milk, carrots, mangoes, orange fruits, sweet potatoes, spinach and other green vegetables are among foods rich in vitamin A.

A variety of Vit A fortified foods, such as breakfast cereals, pastries, breads, crackers, and cereal

Vitamin A Overdose

Although vitamin A is important for health, getting too much vitamin A from supplements can be dangerous and cause

blurred vision, bone pain, dizziness, increased pressure in head and liver problems.

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