Vitamin A found in foods includes members of two chemical families: retinoids and carotenoids. Retinoids include retinol, retinal and retinoic acid and carotenoids include β-carotene, α-carotene and other carotenes. Withal, carotenoid has Vitamin A activity which must be converted into retinoid in the body. So carotenoids are also referred as provitamin A. Though there are hundreds of carotenoids in nature, about fifty could be converted to Vitamin A. Moreover, half dozen of carotenoids are found in human diet in noticeable amounts.
Vitamin A is crucial micronutrient for humans which could not be biosynthesized in body and should be obtained from dietary sources. Moreover, fat soluble essential metabolite and its derivatives has imperative roles in regulation of many biological and metabolic functions including differentiation and growth of cells, reproduction and regulation of immune system. This nutrient is a vital antioxidant which performs corner process essential for protection against oxidative damage caused by free radicals formed in several metabolic processes in human body. Free radicals scavenging are integral for the body’s well-being and fecundity. The vitamin is required to be supplied by natural dietary sources loaded with these micronutrients. Typically retinol and carotenoid levels are measured in plasma and plasma retinol levels used to assess inadequate Vitamin A.
What Foods Provide Vitamin A?
Vitamin A in the retinoid form is found in animal products with the best sources being liver, fish oils, eggs, and vitamin A-fortified milk and milk products. Meanwhile, carotenoids are found in plant sources— mainly in orange and dark green vegetables and some fruits (squash, carrots, spinach, broccoli, papaya, sweet potatoes, pumpkin, cantaloupe, and apricots). In fact, the term carotenoid is derived from the species name for carrots. Nutrition supplements tend to provide vitamin A in the form of retinyl acetate or retinyl palmitate or as β-carotene.
| Food name | Weight (g) | Vitamin A (µg) | DV% |
| Turkey | 113 | 4451 | 635% |
| Margarine | 232 | 3127 | 446% |
| Sweet potato | 328 | 2581 | 368% |
| Carrots | 128 | 1069 | 152% |
| Spinach | 234 | 945 | 135% |
| Apricots | 119 | 753 | 107% |
| Mustard greens | 140 | 738 | 105% |
| Collards | 190 | 722 | 103% |
| Swiss chard | 175 | 536 | 76% |
| Pumpkin | 116 | 494 | 70% |
| Swiss cheese | 132 | 380 | 54% |
| Dandelion greens | 105 | 359 | 51% |
| Turnip greens | 55 | 318 | 45% |
| Parmesan cheese | 100 | 262 | 37% |
| Monterey cheese | 132 | 261 | 37% |
| Egg | 136 | 203 | 29% |
| Feta cheese | 150 | 188 | 26% |
| Garden cress | 50 | 173 | 24% |
| Kale | 118 | 172 | 24% |
| Plantains | 270 | 151 | 21% |
Health Benefits of Vitamin A
Vitamin A is essential for growth, health and maintenance for various reasons:
- Eyesight
Eyes are delicate which requires extra protection and care. Vitamin A is helpful for treating weak eyesight by keeping the eyes moist. Evidence have shown that daily intake of Vitamin A promotes night vision by preventing the chances of night blindness. Eye specialist says that retinol is the only nutrient which assists development of visual purple in eyes. Vitamin A helps to lower the chances of macular degeneration and cataracts which are age associated problems.
- Prevent urinary stones
Urinary stones are considered to be annoying health problem. Every possible precaution to avoid it. The effective way to clear health complication is to consume diet loaded with Vitamin A. It acts as a shield against factors forming urinary calculi by producing calcium phosphate in the body. Vitamin A helps to keep urinary tract in shape by lowering the chances of urinary stone reoccurrence.
- Stronger bones
Vitamin D and dairy products are considered to provide strong teeth and bones. Add dairy products to the diet and drink a glass of milk daily to avoid bone problems. With other nutrients, Vitamin A forms a solid layer known dentin below the surface of teeth. This layer helps to strengthen teeth against various oral health problems.
- Muscle growth
Muscle growth is required for children and growing teens. The proper diet assures proper muscle growth. Vitamin A has numerous health benefits to promote better muscle growth. For muscle growth of growing teens and children, it is essential to add food items to the diet which contains adequate Vitamin A that prevents development of muscular dystrophy in muscles.
- Tissue repair
Body naturally reproduce cells and tissues but requires nutrients for this process. With insufficient nutrients, this process could not take place and body becomes unable to produce new tissues. Moreover, Vitamin A helps to enable this natural process by replacing old tissues with new ones.
- Treatment for measles
Measles is indeed draining which is neither rare nor occurs frequently. Child specialists advise that children with deficiency of Vitamin A are prone to measles. The only solution is to add foods rich in Vitamin A. This vitamin in adequate amounts provides relief from diarrhea and fevers follow with measles.
- Slows aging
As person ages, wrinkles and fine lines become common. Though there are various products as well as treatments to lower the signs of aging but they could not do what a nutrient offers. This makes the beauty experts to trust Vitamin A. It helps to slow down fine lines as well as wrinkles. Naturally, it contains moisture which keeps skin moist. When this moisture is absorbed by skin, one becomes youthful.
- Treatment for acne
Acne is caused by excessive production of sebum and might take months to heal. Supplements of Vitamin A helps to treat acne by limiting the production of sebum on skin. Antioxidants offered by vitamin helps to rejuvenate dead skin cells by leaving smooth and baby soft skin.
- Enhance immunity
Vitamin A acts as an immunity booster. A strong immune system keeps infectious bacteria at bay but one should maintain its functionality. The daily consumption of Vitamin A helps to promote lymphocytic response which counteracts disease causing antigens. It also contains properties which are essential for keeping the mucus membranes moist. The moist mucus membrane promotes better immunity and enhances white blood cells activity. It also prevents reentrance of bacteria and germs in the body.
- Maintain cholesterol level
High level of cholesterol is the contributors to various cardiovascular problems. Various health problems are related with high cholesterol. So nutritionist suggests to intake the diet packed with Vitamin A as it reduces high level of cholesterol. It helps to widen arteries to assure proper blood flow. Vitamin A lowers the risk of blood clotting.
- Offers glowing skin
All vitamins are required to enhance the skin condition so does Vitamin A. Vitamin A is rich in antioxidants as well as healing properties which is must for skin. The diet rich in Vitamin A improve discoloration of skin by providing it a natural glow.
How Much Vitamin A Do We Need?
The RDA for vitamin A is 700 and 900 micrograms for women and men, respectively. During pregnancy and lactation the RDA increases to 770 and 1,300 micrograms respectively. Retinol Equivalents are used because we derive vitamin A from retinoids and carotenoids and REs and the level of activity is not the same for the various forms. For instance, carotenoids are absorbed from the digestive tract with about half the efficiency of the retinoids. Once inside the body, they must be converted to a retinoid, a process that varies in efficiency from one carotenoid to another. In order to account for the inherent differences in obtaining vitamin A activity from retinoids versus the carotenoids, vitamin A is listed in REs. One microgram of retinol equals 1 RE, whereas it takes 12 micrograms of β-carotene to equal 1 RE and 24 micrograms of other carotenes to equal 1 RE. In addition, International Units (IU) are an older method of expressing vitamin activity and are still used on some packaging. One IU is equal to 0.3 micrograms of retinol.
What Happens If Too Little Vitamin A Is Consumed?
When vitamin A is deficient from the diet for many months the body’s internal stores are decreased and deficiency is revealed in the form of:
Night blindness: Night blindness is an inability to adapt to dim lighting and is usually accompanied by a prolonged transition from dim to bright light.
Xerophthalmia: Occurs when the mucus-producing cells of the cornea deteriorate and no longer produce mucus; a hard protein called keratin is produced instead. Keratin in combination with a decreased presence of mucus will dry out and harden the cornea of the eye. Xerophthalmia means dry, hard eyes.
Drying of body linings: Inadequate mucus secretion of cells lining the respiratory, digestive, urinary, and reproductive tracts will greatly affect the function and health of these tissues as well. They are subject to drying and infection. Dry, hard skin is an observable sign of a vitamin A deficiency.
How Common Is Vitamin A Deficiency?
Vitamin A deficiency is one of the more recognized nutrient deficiencies worldwide, as roughly two million children in developing countries go blind each year as a result of vitamin A deficiency. International relief efforts to improve health conditions in these countries are attempting to correct this deficiency by giving children large amounts of vitamin A a couple of times per year. It is hoped that the doses are large enough to provide adequate vitamin A storage to last until the next treatment.
Can Vitamin A Become Toxic?
Toxicity of vitamin A is seemingly just as severe as a deficiency. If a person consumes as little as ten times the RDA for vitamin A for several months, signs and symptoms such as bone pain, hair loss, dryness of the skin, and liver complications may develop. If toxicity persists it can eventually result in death. The risk of vitamin A toxicity from eating a balanced diet is low. Even those of us eating very large amounts of carotenoid-containing fruits and vegetables are not at significant risk of toxicity. This is due to the much lower rate of digestive absorption and conversion of carotenoids to vitamin A. Most people who develop vitamin A toxicity seem to do so through use of supplements. Recently, research has revealed that retinol intakes exceeding 5,000 International Units daily might increase the risk of osteoporosis. Furthermore, vitamin A toxicity during pregnancy can result in birth defects.
References:
http://www.globalresearchonline.net/volume1issue1/Article%20014.pdf
https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/