Introduction:
Vitamin A is well known for the group of fat-soluble retinoids, retinols and retinyl esters. We merely know about vitamin A and its function but speaking of it, it is very important to build immune function, cellular communication (production of cytokines), growth development, reproductive health and vision. It also has antioxidant properties.
There are two forms of vitamin-
Provitamin A – Carotenoids are abundant in plant foods like fruits, vegetables and oils. Provitamin A carotenoids are plant pigments that the body converts into vitamin A in the intestine
Vitamin A – Provitamin A carotenoids in the human diet are beta-carotene, alpha-carotene, and beta-cryptoxanthin, retinol and retinyl esters take place entirely in animal products such as dairy, liver, and fish.
The various forms of vitamin A are solubilized into micelles in the intestinal lumen and absorbed by duodenal mucosal cells. Retinyl esters and provitamin A carotenoids are converted to retinol after uptake into the lumen (for retinyl esters) or absorption (for provitamin A carotenoids). Retinol is then oxidized to retinal and retinoic acid, the two main active vitamin A metabolites in the body
Functions:
How to take:
To take benefits of vitamin A, you should make a balanced diet of vitamin A-containing foods and take benefits of them.
Some vitamin A containing foods are-
Cheese
Eggs
Oily fish
Fortified low-fat spreads
Milk and yoghurt
Yellow, red and green(leafy) vegetables, such as spinach, carrots, sweet potatoes and red peppers contain vitamin A.
Yellow fruit, such as mango, papaya and apricots.
The amount of vitamin A adults aged 19 to 64 need is;
700 milligrams a day for men
600 milligrams a day for women
Storage conditions:
The medicine should be stored at a cool temperature
The duration between two doses:
As vitamin A is stored in the liver, it is suggested to give a high dose of vitamin A once every 4-6 months to prevent vitamin A deficiency. For precaution and safety, the minimum interval between doses should be one month.
If you take supplements of vitamin A, make sure your daily gain from food and supplements does not surpass 1.5mg (1500 milligrams)
Recommended Dietary Allowance (RDA): Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals; often used to plan nutritionally adequate diets for individuals.
Estimated Average Requirement (EAR): Average daily level of intake estimated to meet the requirements of 50% of healthy individuals; usually used to assess the nutrient intakes of groups of people and to plan nutritionally adequate diets for them; can also be used to assess the nutrient intakes of individuals.
Tolerable Upper Intake Level (UL): Maximum daily intake unlikely to cause adverse health effects.
Side effects:
The common symptoms when you take more concentrated supplements. Consult your physician or doctor when you get these symptoms.
bone thinning
liver damage
headache
diarrhea
nausea
skin irritation
pain in the joints and bones
birth defects
Drug mechanism:
Pharmacokinetic:
vitamin A is readily absorbed in the GIT tract.
About less than 5% of circulating vitamin A is bounded to lipoprotein in the blood. When liver stores are saturated because of too much intake. When released from the liver, vitamin A is bound to retinol-binding protein (RBF).
Vitamin A mostly circulate in the form of retinol bound to RBF.
Hepatic retinol is combined with glucuronic acid; the beta-glucuronide goes through enterohepatic circulation and oxidation to retinol and retinoic acid. Retinoic acid undertakes decarboxylation and conjugates with glucuronic acid.
Pharmacodynamics:
Vitamin A is effective for the cure of vitamin A deficiency. Vitamin A refers to a group of fat-soluble substances that are structurally related to and possess the biological activity of the parent substance of the group called all-trans retinol or retinol.
Vitamin A plays a vital role in vision, epithelial differentiation, growth, reproduction, pattern formation during embryogenesis, bone development, hematopoiesis and brain development. It is main important for the maintenance of accurate functioning of the immune system.
When to see a doctor:
Take vitamin A regularly to get the most benefit from it. To help you remember, take it at the same time each day.
Do not increase your dose or use this vitamin A more often than recommended. Your conditions will not improve any faster and your risk of side effects will increase.
For more details consult your physician.
Safety measures:
Allergic reaction:
Although symptoms of vitamin A toxicity may vary, headaches and rash usually develop during acute or chronic toxicity.
Acute toxicity causes increased intracranial pressure.
Drowsiness
irritability
abdominal pain
vomiting
These are some common symptoms sometimes the skin subsequently peels.
Chronic toxicity is sparsely distributed, coarse hair, alopecia of the eyebrows, dry, rough skin.
Because vitamin A is fat soluble, the body stores excess amounts, primarily in the liver, and these levels can accumulate.
Acute vitamin A toxicity, also referred to as hypervitaminosis A, occurs within days to weeks after someone ingests one or a few very high doses (typically more than 100 times the RDA)
Chronic hypervitaminosis A (regular consumption of high doses) can cause dry skin, painful muscles and joints, fatigue, depression, and abnormal liver test results
Available dosage form:
Take medicine as prescribed by your doctor
Tablet – 10,000mg, 15,000mg
Capsule – 7,500mg, 8,000mg, 10,000mg, 25,000mg
Injectable solution – 50,000Units/ml
RAE (retinol activity equivalent)
Males – 900 mcg/day (3000U/day)
Females – above 18 years pregnant 750-770 mcg/day (2500-2600 U/day)
Above 18 years breastfeeding 1300 mcg.
Vitamin A deficiency
Malabsorption or oral administration is not feasible at 100,000Units/day.
IM for 3 days; then 50,000 Units/day for 2 weeks.
Oral therapy – take an oral therapeutic multivitamin containing 10,000 – 20,000 Units/day for 2 months
Deficiency prophylaxis – 10,000 - 50,000Units
Xerophthalmia
Recommended dose except for females of reproductive age – 200,000 units.
Important note:
Vitamin A is also called as retinol
Vitamin A is available in dietary supplements.
Vitamin A supplements can interact with other medicines you take. Be cautious and tell your doctor while taking such medicines.
High intake of vitamin A can be harmful.
Vitamin A has antioxidant properties, and carotenoid-rich fruits and vegetables may protect against particular types of cancer.
Pregnant people need extra vitamin A for fetal growth and tissue maintenance and to support their own metabolism.
Up to 90% of people with cystic fibrosis have pancreatic insufficiency, which increases their risk of vitamin A deficiency due to difficulty absorbing fat.
Approximately one quarter of children with Crohn’s disease and ulcerative colitis have vitamin A deficiency; adults with these disorders, especially those who have had the disorder for several years, also have a higher risk of vitamin A deficiency.
Available brands:
Reference:
Medically reviewed by Jerlyn Jones, MS MPA RDN LD CLT, Nutrition — By Jillian Kubala, MS, RD — Updated on April 24, 2023
Blaner WS. Vitamin A and Provitamin A Carotenoids. In: Marriott BP, Birt DF, Stallings VA, Yates AA, eds. Present Knowledge in Nutrition. 11th ed. Cambridge, Massachusetts: Wiley-Blackwell; 2020:73-91.
Ross A. Vitamin A. In: Ross AC, Caballero B, Cousins RJ, Tucker KL, Ziegler TR, eds. Modern Nutrition in Health and Disease. 11th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2014:260-77.
Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids External link disclaimer. Washington, DC: National Academy Press; 2000.
Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zincexternal link disclaimer. Washington, DC: National Academy Press; 2001.
U.S. Food and Drug Administration. Food Labeling: Revision of the Nutrition and Supplement Facts Labels External link disclaimer. 2016.
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