VITAMIN A AND ITS DERIVATIVES AND THEIR SOURCES
Vitamin A is fat-soluble vitamin which is available in different forms. These different forms are retinoids. These forms include retinol (alcohol), retinal (aldehyde), retinoic acid and retinyl esters. Retinoic acid is unstable one and can be converted into retinol or retinal through reversible reaction.
PRE-VITAMIN
Pre vitamin are those forms of vitamin A which are directly absorbed from small intestine and not required any conversion to act as vitamin A. Retinol and retinyl esters are pre vitamin. Dairy products like milk, butter, cheese, fish, organ meat like liver and eggs are pre vitamin sources of diet.
PRO VITAMIN
Pro vitamin is plants pigment which are inactive precursor and later on convert into vitamin A in small intestine. They are mostly carotenoids. It includes alpha carotene, beta carotene and beta cryptoxanthin.
NON PROVITAMIN
Non provitamin includes lycopene, lutein and zeaxanthin. Non provitamin are those carotenoids which are not involve in formation of vitamin A. Carotenoids present in the cell wall of fruits are easily absorb unlike the present in dark green leafy vegetables and carrots which are not readily released in the body.
VITAMIN A SUPPLEMENTS
Vitamin A supplements mostly contain pre vitamin and provitamin combination
VITAMIN A DEFICIENCY AND MALIGNANCY
Vitamin A is a very good antioxidant and has a critical role in cell differentiation so, it was supposed to be a very good preventive micronutrient against the cancer. How vitamin A deficiency causes cancer, the following role of vitamin A in the body support the above-mentioned statement.
VITAMIN A AND CELL DIFFERENTIATION
Vitamin A has a critical and important role in cell differentiation. It plays a vital role in controlling of cell differentiation processes. Loss of this control will result in abnormal growth of cell which is malignancy or in other words, it is formation of cancerous cell.
VITAMIN A AND OXIDATION
Vitamin A is very good antioxidant. Oxidation/ peroxidation/ auto oxidation cause gradual change in cell means it is initiative of process of cancer because now cell became cancerous. Vitamin A inhibits this oxidation process because it has high content of carbon with number of double bonds.
VITAMIN A AND KERATIN
As we already discussed, Vitamin A control the process of cell differentiation. Keratin is protein which is helpful in forming the tissues of the hairs, nails and the outer layer of the skin. It is also present on epithelial cell in the lining of organs and glands such as lungs, breast, colorectal, bladder and head and neck. Vitamin A deficiency induce specific keratin species and there are morphological changes on the epithelial cells which means there is abnormal growth of cell. Keratin is type of tumor marker. In different types of cancer, certain keratins may be found higher than normal amounts.
GLYCOSYLATED DERIVATIVES OF VITAMIN A
Due to pollution, genetic disorders, toxins and imbalance diet there are continuous changes in the cell without any interruption if a person is vitamin A deficient. Vitamin A is required in the formation of mucus (mucus polysaccharides) and glycoprotein which keep epithelial surface smooth. In other words, it keeps the cell membrane healthy. Retinol after receiving mannose became phosphorylated and form glycosylated derivatives of vitamin A which is Mannosyl retinyl phosphate which inhibit certain changes in cell and inhibit cancerous cell formation.
VITAMIN A AND NATURAL KILLER CELL
Natural killer cells are very important part of immune system. They are very effective against infection and cancer. If there is any abnormality then natural killer cell that abnormal cell or cancerous cell. Vitamin A is required for nasal natural killer cells number and activity.
HOW VITAMIN A DEFICIENCY INDUCE CANCER IN SMOKER
Cigarettes smoke decreased vitamin A in the body. Due to this deficiency, there will be neoplastic changes in the epithelium of trachea and bronchi. Vitamin A deficiency causes decrease expression of retinoic acid beta receptors which promote transcription of tumor suppressor gene and increased expression of retinoic acid alpha receptors. In this way, vitamin A deficiency in smokers increase the risk of lung cancer.
BETA CAROTEEN SUPPLEMENTS AND CANCER
Increase intake of vitamin supplements can increase the risk of lungs cancers. Usually, people use these vitamins supplements to improve immunity and eye 👁 sights. What the experts say about it, have a look.
PEKING UNIVERSITY OF CHINA
However, the experts of PEKING UNIVERSITY OF CHINA warn the people that these vitamins supplements may be the causative factor of lungs cancer. In the last Research, it was found that excessive use of vitamin A supplements can increase the risk of uterus cancer but it is first time that some connections between vitamin A supplements and lungs cancer has been found.
FRONTIER IN NUTRITION
According to research that is published in FRONTIER IN NUTRITION increase intake of vitamin A supplements can increase the risk of squamous cells and adenocarcinoma lungs cancer. Lung cancer is the major factor of death in Britain besides the other types of cancer. Every year, approximately 47 thousand peoples in Britain diagnosed with lung cancer and around 34 thousand and 700 people died because of it. Squamous and adenocarcinoma are very common type of lung cancer.
INTERNATIONAL AGENCY FOR RESEARCH ON CANCER
In 1998, the IARC concluded that supplements of beta carotene at high doses (greater or equal to 15mg / day) loses it cancer preventive activity. High doses of beta carotene increased risk of LUNG CANCER among smokers and asbestos workers.
WORLD CANCER RESEARCH FUND
In 2007, the WCRF concluded that there is valid relation between beta carotene supplements and increased risk of LUNG CANCER in the light of studies which shows that there is noticeable relation between beta carotene, smoking and genotype. People who are smokers and lacking the carcinogen-detoxifying enzymes glutathione-S transferase 1 and 2 due to genetic variation have a great risk of lung cancer. Use of high dose supplements of vitamin A (greater than 20 mg / day of beta carotene) in smokers showed increased risk of LUNG CANCER than in smokers taking low doses of vitamin A. According to WCRF, beta carotene supplements were unexpectedly also showing a fundamental effect on other types of cancer such as prostrate and non-melanoma skin cancers.
A META-ANALYSIS OF 2010
A meta-analysis of 2010 also indicated the convincing relation between high dose of vitamin A supplements and increased lung cancer mortality. Other studies also show the strong relation between beta carotene supplements and various types of cancers like bladder cancer, stomach cancer and bowel adenoma. These effects become amplify in smokers and asbestos workers
WORLD HEALTH ORGANIZATION
According to WHO experts reports of 2003 there is insufficient evidence that carotenoids decreased the risk of cancer. WHO does not mention whether insufficient evidence is for vitamin A supplements or for dietary carotenoids.
DIETARY BETA CAROTEEN AND RISK OF CANCER
Dietary beta carotene reduces the risk of lung cancer or other types of cancer. There are some studies which support that dietary beta carotene decreased risk of cancer.
IN UNITED STATES OF AMERICA
In USA, raw fruits and vegetables (dietary beta carotene) reduces the risk of lungs cancer in non – smoking men and women.
WORLD CANCER RESEARCH FUND
According to WCRF, the dietary carotenoids were probably protective against various types of cancer such as lungs, mouth, pharynx, larynx and esophageal cancer and reduce the risk of cancer.
RECOMMENDATION OF CANCER COUNSIL
- Cancer council recommend to the get nutritional requirements from the food rather than from supplements
- Avoid taking high doses that is greater than 18mg/ day of beta carotene especially for smokers.
- People should take a wide variety of fruits and vegetables to obtain maximum benefits.
CONCLUSION
In last, I concluded that deficiency of Vitamin A can cause the cancer because of its critical role in cell differentiation and regulation. But vitamin A supplements increase the risk of lung cancer especially in smokers while dietary carotenoids reduce the risk of cancer especially lung cancer Vitamin A shows dose dependent effects on smokers. Extensive research is required to established the safe limit of beta carotene supplements use and to establish the fact that what difference is exist between natural and supplements beta carotene. What is the possible mechanism of action of natural and supplements beta carotene Many answers have been awaited about the role of VITAMIN A in cancer.