Actions of Vitamin A in details
Vision:Vitamin A (all-trans Vitamin A) is converted in the retina to the 11-cis-isomer of retinaldehyde or 11-cis-retinal. 11-cis-retinal functions in the retina in the transduction of light into the neural signals necessary for vision. 11-cis-retinal, while attached to opsin in rhodopsin is isomerized to all-trans-retinal by light. This is the event that triggers the nerve impulse to the brain which allows for the perception of light. All-trans-retinal is then released from opsin and reduced to all-trans-Vitamin A. All-trans-Vitamin A is isomerized to 11-cis-Vitamin A in the dark, and then oxidized to 11-cis-retinal. 11-cis-retinal recombines with opsin to re-form rhodopsin. Night blindness or defective vision at low illumination results from a failure to re-synthesize 11-cis retinal rapidly. Epithelial differentiation: The role of Vitamin A in epithelial differentiation, as well as in other physiological processes, involves the binding of Vitamin A to two families of nuclear retinoid receptors (retinoic acid receptors, RARs; and retinoid-X receptors, RXRs). These receptors function as ligand-activated transcription factors that modulate gene transcription. When there is not enough Vitamin A to bind these receptors, natural cell differentiation and growth are interrupted.
How should I take Vitamin A?
Use exactly as directed on the label, or as prescribed by your doctor. Do not use in larger or smaller amounts or for longer than recommended.
Swallow the tablet or capsule whole.
Measure liquid medicine with a special dose-measuring spoon or medicine cup, not with a regular table spoon. If you do not have a dose-measuring device, ask your pharmacist for one.
Never take more than the recommended dose of Vitamin A. Avoid taking more than one vitamin product at the same time unless your doctor tells you to. Taking similar vitamin products together can result in a vitamin overdose or serious side effects.
Your healthcare provider may occasionally change your dose to make sure you get the best results from Vitamin A. The recommended dietary allowance of Vitamin A increases with age. Follow your healthcare provider's instructions. You may also consult the National Academy of Sciences "Dietary Reference Intake" or the U.S. Department of Agriculture's "Dietary Reference Intake" (formerly "Recommended Daily Allowances" or RDA) listings for more information.
Store at room temperature away from light, moisture, and heat.
Vitamin A administration
Use exactly as directed on the label, or as prescribed by your doctor. Do not use in larger or smaller amounts or for longer than recommended.
Swallow the tablet or capsule whole.
Measure liquid medicine with a special dose-measuring spoon or medicine cup, not with a regular table spoon. If you do not have a dose-measuring device, ask your pharmacist for one.
Never take more than the recommended dose of Vitamin A. Avoid taking more than one vitamin product at the same time unless your doctor tells you to. Taking similar vitamin products together can result in a vitamin overdose or serious side effects.
Your healthcare provider may occasionally change your dose to make sure you get the best results from Vitamin A. The recommended dietary allowance of Vitamin A increases with age. Follow your healthcare provider's instructions. You may also consult the National Academy of Sciences "Dietary Reference Intake" or the U.S. Department of Agriculture's "Dietary Reference Intake" (formerly "Recommended Daily Allowances" or RDA) listings for more information.
Store at room temperature away from light, moisture, and heat.
Vitamin A pharmacology
Beta-carotene, Vitamin A, and retinal have effective and reliable Vitamin A activity. Retinal and Vitamin A are in chemical equilibrium in the body and have equivalent antixerophthalmic activity. Retinal combines with the rod pigment, opsin, in the retina to form rhodopsin, necessary for visual dark adaptation. Vitamin A prevents retardation of growth and preserves the epithelial cells’ integrity. Normal adult liver storage is sufficient to satisfy two years’ requirements of Vitamin A.
Vitamin A is readily absorbed from the gastrointestinal tract, where the biosynthesis of Vitamin A from beta-carotene takes place. Vitamin A absorption requires bile salts, pancreatic lipase, and dietary fat. It is transported in the blood to the liver by the chylomicron fraction of the lymph. Vitamin A is stored in Kupffer cells of the liver mainly as the palmitate. Normal serum Vitamin A is 80–300 Units per 100 mL (plasma range is 30–70 mcg per dl) and for carotenoids 270–753 Units per 100 mL. The normal adult liver contains approximately 100 to 300 micrograms per gram, mostly as Vitamin A palmitate.
*Oil-soluble Vitamin A water solubilized with polysorbate 80.
References
- DailyMed. "ASCORBIC ACID; BIOTIN; CYANOCOBALAMIN; DEXPANTHENOL; ERGOCALCIFEROL; FOLIC ACID; NIACINAMIDE; PHYTONADIONE; PYRIDOXINE HYDROCHLORIDE; RIBOFLAVIN 5'-PHOSPHATE SODIUM; THIAMINE HYDROCHLORIDE; VITAMIN A; VITAMIN E: DailyMed provides trustworthy information about marketed drugs in the United States. DailyMed is the official provider of FDA label information (package inserts).". https://dailymed.nlm.nih.gov/dailyme... (accessed September 17, 2018).
- NCIt. "Retinol: NCI Thesaurus (NCIt) provides reference terminology for many systems. It covers vocabulary for clinical care, translational and basic research, and public information and administrative activities.". https://ncit.nci.nih.gov/ncitbrowser... (accessed September 17, 2018).
- EPA DSStox. "Retinol: DSSTox provides a high quality public chemistry resource for supporting improved predictive toxicology.". https://comptox.epa.gov/dashboard/ds... (accessed September 17, 2018).
Reviews
The results of a survey conducted on ndrugs.com for Vitamin A are given in detail below. The results of the survey conducted are based on the impressions and views of the website users and consumers taking Vitamin A. We implore you to kindly base your medical condition or therapeutic choices on the result or test conducted by a physician or licensed medical practitioners.User reports
1 consumer reported administration
When best can I take Vitamin A, on an empty stomach, before or after food?ndrugs.com website users have also released a report stating that Vitamin A should be taken After food. In any case, this may not be the right description on how you ought to take this Vitamin A. Kindly visit your doctor for more medical advice in this regard. Click here to see other users view on when best the Vitamin A can be taken.
| Users | % | ||
|---|---|---|---|
| After food | 1 | 100.0% | |
Consumer reviews
There are no reviews yet. Be the first to write one! |
Information checked by Dr. Sachin Kumar, MD Pharmacology
