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Can Vitamin-A Prevent Cancer?

by G.S. Mudur
VITAMIN A which h« helped the world com bat night blindness ml ght soon figure on doctor*' list* a* a cancer preventive agent Thia follow* medical studies linking the high con sumption of vitamin A compound* with reduced cancer risk
Studies on the effect of vitamin A deficiency on laboratory animal* have now given way to detailed investigations on how the two classes of vitamin A compound*, the retinoid* and the carotenoid*, might have a protective effect against cancer
Studies on laboratory animal* decades ago showed that vitamin A deficiency could lead to premallgnant changes In the respiratory, gastrointestinal and genitourinary tracts Such studies also indicated that the administration of retinoids could lead to the regression of induced tumours and delay the appearance of transplanted tumours
Evidence of the chemopre-venttve effect of retinoids in
human* has come from several clinical trial* of tooicgl retinoid* which have been shown to be effective in reversing malignant and ptemallgnant change* tn the skin A report tn the medical
Journal cancer said oral administration of retinoids seemed to produce a beneficial effect on several cancerous and precancerous conditions.
The Inverse link between carotenoids and retinoid* and the risk of cancer was also evident from a study conducted in the Philippines by a team of Canadian scientists who stud led chromosomal changes in a population of regular chewer* of betel quid, made up of the areca nut and the betel leaf.
The scientists examined structures called micronuclei tn the cells scraped from the Inner cheeks of the betel quid chewers who were presumed to be at a high risk of developing oral cancer because of their chewing habit These ml
cronuclel are indicators of damage to the DNA and appear long before any cancerous changes become evident
In the study, the scientists supplemented the diet of a group of regular beta quid chewer* for three month* with sealed capsule* of retinol and beta carotene. This resulted tn a three fold decrease in the average proportion of cell* with micronuctet. The study was repeated to test with retinol and carotene separately and a similar reduction tn chromosomal breakage was "found for both these com pound* The sciejit'*1* found that these vitamin A compounds, appeared to be effec ttve as an inhibitors of micronuclei cell formation.
Researchers are now exploring theories on the possible mechanisms of action by which the retinoid* and the carotenoid* produce a protective effect againist cancer.
Retinol and other retinoid* play a rote tn cell growth and
cell differentiation which might affect carcinogenesis. Such a rote for retinoid ha* been supported through labo ratory tests In which retinoids Inhibit malignant transformations induced In cultured cell*
Carotenoid*, the biological precursor* of vitamin A are found tn vegetables and fruit*, and they are converted into retinol in the body. Researchers believe thia increase tn retinol level In the body could be one Indirect way by which they reduce the risk of cancer.
But beta carotenoid has the ability to trap some organic free radicals and to deactivate excited oxygen molecules which are generated as a byproduct of many normal metabolic processes So. •dentist* believe that free carotene tn the body might also have a direct protective effect against the onset of cancer by deactivating these molecules or pre venting damage by oxidation.
Most of the data on preven-
tive action of beta carotene comes from epidcmloiotglcal studies of dietary vitamin A which could be regarded a* a measure of the Intake of beta carotene. According to the report in the Journal Cancer, the strongest and most consistent evidence of a protective effect of high Intake of carotene rich foods come* from studies of lung cancer and cancer of the esophagus.
But doctors are not making any conclusion* yet. The re searchers who studied the inverse relationship between serum carotenoid and subsequent lung cancer three year* ago speculated that the protective effect* of beta carotene against lung cancer could be due to other micronutrients tn green or yellow vegetables that are highly correlated to beta carotene. Trial* involving thou •and* of people are now under way and a final answer to whether vegetables rich In vitamin A like carrots can indeed keep cancer away might itself be year* away