Vitamin A is a fat soluble vitamin which is very essential for our body. Vitamin A in animal foods (meat, milk and eggs) is mainly in the form of retinol combined with fatty acid. In the body retinol can be converted to retinal or retinoic acid, both of which have specific functions, retinal plays a central role in function of the retina, while retinoic acid helps regulate gene expression and cell development. All of these compound retinol, retinal, and retinoic acid are referred to collectively as vitamin A.
Functions of vitamin A
Vision – in the eye vitamin A plays a central role in the transformation of light energy in to the nerve impulse the brain perceives as vision. The rod and cone cells of the retinal epithelium are rich in retinal. When light enters the eye, a molecule of retinal absorbs the energy and changes shape, triggering a nerve impulse.
Skin and mucus membrane health – vitamin A promotes proper growth and development of the cells lining the skin and mucus membrane in the respiratory, gastrointestinal, and genitourinary tracts. It plays a central role in maintaining the health and integrity of the skin.
Reproduction – optimum vitamin A status maintains sperm count and motility in males. In females, deficiency is associated with infertility and spontaneous abortion.
Immune system – vitamin A increase resistance to infection by maintaining the integrity of the skin and mucus membrane barriers against bacteria, viruses, and parasites. In addition, vitamin A enhances antibody production by white blood cells and increases the number of activity of T cells.
Hormone synthesis – vitamin A is required for steroid hormone synthesis, including production of corticosteroids in the adrenal gland and androgens and estrogen in the testes and ovaries.
Growth and development – vitamin A controls cell growth and development. Children deficient in vitamin A fail to grow and develop normally.
Nervous system – vitamin A helps maintain the protective sheath (MYELIN) around nerves, both in peripheral nerves and in the brain.
Red blood cells – vitamin A plays an important role in mobilizing iron stores to build new red blood cells.
Skeleton – vitamin A participates in bone formation, particularly during childhood growth and during fracture healing.
Foods with Vitamin A
The common foods that are rich source or Vitamin A are:
Beef liver, fish liver oil, fortified cereal, egg yolk, animal livers, dairy products, butter and fortified margarine, cheddar cheese, and cream.
Vitamin A deficiency
Children and adolescents are particularly at risk or Vitamin A deficiency. If children’s diet are low in vitamin A, deficiency develops quickly.
Stress, infection, or surgery increases vitamin A requirements
Newborns particularly premature infants have very low stores of vitamin A and do not absorb vitamin A efficiently.
Fat Malabsorption due to liver or biliary disorders, Crohn’s disease, and chronic pancreatitis causes poor absorption of vitamin A.
In diabetes and hypothyroidism
Heavy alcohol consumption interferes with absorption, storage, and metabolism of vitamin A.
Cigarette smoking and air pollution increases requirements for vitamin A. toxic metals, such as cadmium, increases breakdown and loss of vitamin A from the body.
Repeated and lengthy exposure to bright sunlight, particularly in lighter skinned people, breaks down beta-carotene in the skin and retinal in the eyes.
Many drugs interfere with vitamin A metabolism. For example, cholesterol-lowering drugs and laxative decrease absorption.
Signs and symptoms of deficiency of vitamin A
- Dryness, itching and redness of the conjunctiva
- Inability to adapt to and see in dim light (night blindness)
- Dry, rough, itchy skin with rash
- Dry, brittle hair and nails
- Loss of sense of smell, taste, and appetite
- Poor growth
- Increased vulnerability to infections
- Increased risk of cancer of the throat, lung, bladder, cervix, prostate, esophagus, stomach, and colon
- Impaired reproduction and fertility
- Increased risk of kidney stones
Signs of excess of vitamin A
- Peeling of skin
- Enlarged spleen and kidney
- Bone thickening and joint pain
- Drying of the mucus membrane
- Liver damage
Vitamin A is known for its teratogenic affects; if pregnant women are using a supplement, they should consider taking it in the form of beta carotene. Caution should be given to supplement use in women of childbearing age because many women don’t know they are pregnant in the earlier stages. Supplements with retinol should be avoided during the first trimester if vitamin A deficiency is not present.
Use of vitamin A in prevention and therapy
Infectious diseases – infections of the skin (acne, fungal infection, impetigo, boils), influenza, conjunctivitis, ear infections, bronchitis and pneumonia, infectious diarrhoeal disease may benefit from vitamin A.
Skin and scalp/hair disorder – vitamin A helps maintain skin health and may be beneficial in cases of dry skin, dandruff, premature aging of skin, eczema, and psoriasis.
Traumatic injury – vitamin A plays a major role in the healing of wounds and bony fractures.
Gynecological disorders – vitamin A may be beneficial in reducing menstrual symptoms and benign fibrocystic breast disease.
Protection against carcinogens – vitamin A is one of nature’s primary anti cancer substances, particularly in the skin and mucus membrane.
Respiratory disorders – vitamin A may reduce symptoms and severity of chronic obstructive pulmonary disease and asthma, particularly in regular smokers.
Gastric ulcers – vitamin A helps maintain gastric mucus production and may reduce stress ulceration in traumatized or burned patients.
Cataract – ample intake of vitamin A and beta-carotene may reduce the risk of cataract.
Anemia – the combination of iron plus vitamin A may be more effective than iron alone in treating iron-deficiency anemia.