Vitamin A can be very helpful in our life :
Maintenance of normal vision -
- Our eyes need vitamin A to function effectively as vitamin A is involved in the production of a chemical called visual purple, which helps us to see in dim light.
- Growth, repair and cell differentiation Vitamin A is necessary for the growth and repair of many body cells including those of bones, teeth, collagen and cartilage.
- It is also essential for a process known as cell differentiation in which un-specialised cells are modified so that they can perform specific functions.
- Thus vitamin A plays a central role in tissue development and maintenance.
Health of epithelial cells -
- Vitamin A is vital for the formation of healthy epithelial cells.
- These cells cover the internal and external surfaces of the body and are found in the skin, lungs, developing teeth, inner ear, cornea of the eye, sex organs, glands and their ducts, gums, nose, cervix and other areas.
- Many epithelial cells produce mucus which is necessary to lubricate body surfaces and protect against invading micro-organisms. For example, the good health of the digestive tract lining is important in protecting against ulcers, and maintenance of the lining of the vagina and uterus is important in fertility.
Pregnancy and fetal development -
Because of its vital role in cell development and differentiation, adequate vitamin A helps to ensure that the changes which occur in the cells and tissues during fetal development take place normally. It may be involved in cell to cell communication.
Protection against infection -
Known as 'the anti-infective vitamin', vitamin A plays an essential role in protecting your body from infection. It keeps body surfaces healthy so they can act as barriers to invading micro-organisms.
Vitamin A stimulates and enhances many immune functions including antibody response and the activity of various white blood cells such as T helper cells and phagocytes. This immune-enhancing function promotes healing of infected tissues and increases resistance to infection.
Other actions -
Laboratory experiments have shown vitamin A to have antiviral activity. Vitamin A also has antioxidant activity and has a role in protecting against free radical damage which contributes to many common diseases. Vitamin A is involved in iron metabolism and storage.
Absorption and metabolism -
The presence of fat and bile in the intestines is necessary for vitamin A absorption. Around 80 to 90 per cent of vitamin A in the diet is absorbed, although this is reduced in older people and those who have trouble absorbing fat, such as pancreatitis, celiac disease and cystic fibrosis sufferers, who may run the risk of vitamin A deficiency. Vitamin A is joined to fatty acids in the intestinal lining, combined with other substances and transported to the liver, which stores 90 per cent of the body's vitamin A.
Aspects of deficiency.
Eyes -
One of the first symptoms of deficiency is night blindness due to lack of visual purple. Prolonged deficiency leads to xerophthalmia, a condition in which eyes become dry, ulcers appear on the cornea, the eyelids become swollen and sticky, and which eventually leads to blindness. Vitamin A deficiency is the leading preventable cause of blindness in developing countries.
Skin -
Prolonged deficiency leads to thickened dry skin which is prone to infections. Small hardened bumps of a protein known as keratin may develop around the hair follicles.
Growth -
Deficiency causes growth retardation; weight loss; diarrhoea, thickening of bone shafts; congenital malformations; impaired hearing, taste and smell; wasting of testicles; and reduced sperm count. Inadequate vitamin A intake can lead to improper tooth formation in children and to gum disease.
Immune system -
Epithelial surfaces are adversely affected by vitamin A deficiency, causing increased susceptibility to skin and respiratory infections.
Immune cells and antibody functions are also affected which may lead to an increase in pre-cancerous cells in the epithelial tissues of the mouth, throat and lungs.
Many studies have shown that vitamin A deficiency is associated with increased risk of infection in developing countries.
HIV -
Vitamin A deficiency is often seen in HIV-positive people and this may be due to metabolic changes associated with HIV infection.
A 1995 study done on HIV-infected drug users in the US found that there was a higher risk of death in those with vitamin A deficiency.
Vitamin A deficiency is often seen in HIV-positive pregnant women and severe deficiency increases infant mortality and the risk of mother-to-child transmission of HIV.
Thyroid gland -
A deficiency of vitamin A can contribute to lower levels of active thyroid hormone with symptoms of low body temperature, depression, difficulty with weight loss, headaches and lethargy.
Cancer -
Many studies suggest that high blood levels of vitamin A can help prevent certain forms of cancer, particularly cancers of epithelial tissue. This may be due to the importance of vitamin A in maintaining healthy epithelial cells, strengthening the immune system and stimulating the response to abnormal cells. Vitamin A deficiency may also increase the risk of breast cancer.
Lung cancer -
Vitamin A-related compounds known as retinoids. Of the six different types of retinoid receptors, three were found at lower levels in cancer cells.
This studies have reflected the possibility that increasing dietary intake of vitamin A or taking supplements can be used to reduce the risk of lung cancer.
Lung function -
Vitamin A supplements may be useful in treating chronic obstructive pulmonary disease.
Heart Disease -
Low blood levels of vitamin A may be associated with the development of heart disease.
Arthritis -
Vitamin A levels have also been found to be low in rheumatoid arthritis and systemic lupus erythematosus sufferers.
Leukoplakia -
Vitamin A has also been shown to exert protective effects against leukoplakia, a pre-cancerous change in mucous membranes. It often occurs in the mouth and throat and is related to smoking.
Immunity -
Adequate vitamin A intake, either from diet or supplements, is very important in boosting immunity and preventing sickness and death in children.
Vitamin A eye drops have been used to treat eye problems including blurred vision, cataracts, glaucoma, conjunctivitis and dry eyes.
Other disorders for which vitamin A has been tried include asthma, sebaceous cysts, fibrocystic breast disease and premenstrual syndrome. Vitamin A may also be useful in the prevention of ulcers.
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