Vitamin A is a fat-soluble nutrient that plays vital role in your body. It is an essential nutrient needed in small amounts by humans for the normal functioning of the visual system; growth and development; and maintenance of epithelial cellular integrity, immune function,and reproduction. It is a powerful antioxidant and acts as a hormone in the body, affecting the expression of genes and thereby influencing phenotype.
Types of Vitamin In general,
There are two types of vitamin A,depending on the type of food source it comes from. Vitamin A from animal-derived foods is called retinol. This "pre-formed" vitamin can be used directly by the body.
Good food sources of retinol vitamin include beef and chicken liver, whole milk and cheese. Vitamin A obtained from colorful fruits and vegetables is in the form of "pro vitamin A" carotenoids, which are converted to retinol by the body after the food is ingested.
Good food sources of pro vitamin A carotenoids include carrots, sweet potatoes, spinach, kale and cantaloupes. Beta-carotene Beta-carotene is one of the most prevalent and effective pro vitamin A carotenoids. The name beta carotene comes from the Greek"beta" and Latin "carota" (carrot).
It is the yellow/orange pigment that gives vegetables and fruits their rich colors. Beta carotene is an antioxidant that converts to vitamin A and plays a very important role in health. It’s responsible for the red, yellow, and orange coloration of some fruits and veggies.
Beta carotene may prevent skin damage and contribute to maintenance of skin health and appearance. Taking beta carotene may reduce sun sensitivity for certain people who photosensitive diseases. It may also reduce the effect of phototoxic drugs.
Beta carotene may slow cognitive decline and help older people retain their lung strength as they age. Age-related maculardegeneration (AMD) is a disease that affects vision. Taking high doses of betacarotene in combination with vitamin C, vitamin E, zinc, and copper may reduce the risk of advanced AMD by 25 percent.
The following foods are rich in beta carotene: apricots,asparagus, broccoli, carrots, grapefruit, oregano, parsley , onions, peas , peppers,plums, pumpkin, spinach and sweet potatoes. Leafy greens and orange-colored fruits, such as cantaloupes, papayas,and mangoes are rich sources of vitamin A.
Vision Vitamin A is required for the maintenance of normal vision. A deficiency in vitamin A can lead to visual disturbances. In the eyes, a form of vitamin A called retinal is combined with a protein called opsin to give rhodopsin, an essential light absorbing molecule needed for color vision and seeing in dim light.
Measles
Measles is a leading cause of childhood morbidity and mortality. Vitamin A deficiency is a recognized risk factor for severe measles. When children with vitamin A deficiency get measles, the disease tends to be more severe. In these children, taking supplements with high doses of vitamin A can shorten the fever and diarrhea caused by measles.
These supplements can also lower the risk of a reduced risk of overall mortality and pneumonia specific mortality in children with measles who live in developing countries where vitamin A deficiency is common. The effect is greater in children under the age of two years.
The World Health Organization recommends administration of an oral dose of 200,000 IU (or 100,000 IU in infants) of vitamin A per day for two days to children with measles in areas where vitamin A deficiency may be present.
Vitamin A Deficiency
As vitamin A affects a wide range of body functions, a deficiency can lead to a variety of problems. These include: night blindness ,a higher risk of infections, especially in the throat, chest, and abdomen , follicular hyperkeratosis, leading to dry, bumpy skin ,fertility issues and delayed growth in children.
Vitamin A deficiency is common in many developing countries, often because residents have limited access to foods containing preformed vitamin A from animal-based food sources and they do not commonly consume available foods containing beta-carotene due to poverty.
According to the World Health Organization, 190 million preschool-aged children and 19.1 million pregnant women around the world have vitamin A deficiency. Low vitamin A intake is most strongly associated with health consequences during periods of high nutritional demand,such as during infancy, childhood, pregnancy, and lactation.
In developing countries, vitamin A deficiency typically begins during infancy, when infants do not receive adequate supplies of colostrum or breast milk.Chronic diarrhea also leads to excessive loss of vitamin A in young children, and vitamin A deficiency increases the risk of diarrhea. Vitamin A deficiency is one of the top causes of preventable blindness in children.
The most common symptom of vitamin A deficiency in young children and pregnant women is xerophthalmia. Vitamin A deficiency also increases the severity and mortality risk of infections(particularly diarrhea and measles) even before the onset of xerophthalmia.
Some groups are at risk of vitamin a inadequacy.In women with vitamin A deficiency, breast milk volume and vitamin A content are suboptimal and not sufficient to maintain adequate vitamin A stores in infants who are exclusively breastfed.
The prevalence of vitamin A deficiency in developing countries begins to increase in young children just after they stop breastfeeding. Pregnant women need extra vitamin A for fetal growth and tissue maintenance and for supporting their own metabolism.
Other effects of vitamin A deficiency in pregnant and lactating women include increased maternal and infant morbidity and mortality, increased anemia risk,and slower infant growth and development.
Premature Infants do not have adequate liver stores of vitamin A at birth and their plasma concentrations of vitamin A often remain low throughout the first year of life. Preterm infants with vitamin A deficiency have an increased risk of eye, chronic lung, and gastrointestinal diseases Lowering cancer risk
Adequate intakes of carotenoids from fruits and vegetables are associated with a lower risk of lung cancer and prostate cancer but the use of beta-carotene and vitamin supplements have not shown the same results. Studies in Japan have suggested that beta-carotene may help prevent colon cancer.
Role of Vitamin A in the Immune System Vitamin A was initially coined “the anti-infective vitamin” because of its importance in the normal functioning of the immune system. The skin and mucosal cells, lining the airways, digestive tract, and urinary tract function as a barrier and form the body's first line of defense against infection.
Vitamin A is essential for maintaining healthy immune function and deficiency can lead to an impaired response to infection.Vitamin A is involved in the development of the immune system and plays regulatory roles in cellular immune responses and humoral immune processes.
The epithelium lines all outer surface and most inner surfaces of organisms, and it functions as the “front line” of defense against pathogen invasion. Studies from recent years have shown that vitamin A plays a crucial role in the morphological formation of the epithelium and functional maturation of epithelial cells.
As a promoter for morphology and a cell differentiation enhancer, vitamin A is an integral part of the mucus layer of both the respiratory tract and the intestine. Since vitamin A promotes mucin secretion, it improves the immunity function of these tissues. Research has shown that vitamin A improves the mechanistic defense of the mucosa and increases the integrity of intestinal mucus.
The Overdose Risks of Vitamin A Supplements Hypervitaminosis A (vitamin A toxicity) is a condition that occurs when a person has too much vitamin A in their body. This can happen if a person takes too many supplements or uses certain creams foracne over a prolonged period.
A healthful, balanced diet should provide enough vitamin A without needing supplements. Vitamin A supplements are available for those who have difficulty absorbing the nutrient, but it is best to meet needs through food, not in isolation.
Over consumption of vitamin A can be toxic as it can lead to: skin changes( such as yellowing, cracking, itching, and heightened sensitivity to sunlight ), vision changes, brittle nails ,hair changes( like hairless and oily hair ), weak bones, bone pain, or swelling , vomiting, dizziness,headaches, and nausea , difficulty gaining weight , decreased appetite, mouth ulcers, gum disease, irritability, fatigue, drowsiness, changes in alertness , liver disease, in cases of extremely excessive intake.
For children, additional symptoms may include: soft skull, coma, bulging-eyeballs, double vision, and a bulging soft spot on a baby's head. Pregnant women should not consume more than the recommended levels of Vitamin A because retinol has been linked with fetal deformities. Beta-carotene and other carotenoids are not as toxic as retinol, as these are only converted into vitamin A when it is needed.
The highest risk is with supplements. Higher intakes of beta carotene have been linked to higher incidence of lung cancer for smokers, but food sources are always the safest source of beta carotene. Those who take Isotretinoin, for acne treatment should take care not to consume too much vitamin A, and to avoid vitamin A supplements, because this drug is a vitamin A derivative.
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