Vitamin A
Vitamin A
Snapshot
Vitamin A is a fatβsoluble micronutrient essential for vision, immune function, cellular growth, and skin health through its active forms retinol and retinal.
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What is Vitamin A?
Vitamin A refers to a group of compounds including retinol, retinaldehyde (retinal), and retinoic acid, along with provitamin A carotenoids such as betaβcarotene. These molecules play critical roles in phototransduction, gene expression, and epithelial maintenance.
Where It Comes From
Preformed vitamin A (retinol and retinyl esters) is sourced from animal foods like liver, dairy products, and fish oils. Provitamin A carotenoids are found in colorful fruits and vegetablesβcarrots, sweet potatoes, spinach, and kaleβwhere they are enzymatically converted to active forms in the body.
Key Nutrients & Compounds
Provides retinol (supports vision cycle), retinal (visual pigment precursor), retinoic acid (regulates gene transcription), and betaβcarotene (antioxidant carotenoid and provitamin A).
Health Benefits
Vitamin A maintains healthy vision by forming rhodopsin in retinal photoreceptors; supports innate and adaptive immunity by preserving mucosal barriers and lymphocyte function; promotes normal cellular differentiation in skin and epithelia; and contributes to reproductive health and embryonic development.
Recommended Dosage
The adult Recommended Dietary Allowance is 900β―Β΅gβ―RAE (retinol activity equivalents) per day for men and 700β―Β΅gβ―RAE/day for women. Upper intake level is 3,000β―Β΅gβ―RAE/day to avoid toxicity. One RAE = 1β―Β΅g retinol or 12β―Β΅g dietary betaβcarotene.
How to Use It
Obtain vitamin A from a balanced diet including animal sources and colorful produce. For supplementation, take with a meal containing dietary fat to enhance absorption. Monitor total intake from all sources to remain within safe limits.
Who Should Use It?
Individuals with limited animal food intake (e.g., strict vegans), those with fatβmalabsorption disorders, or in regions with vitamin Aβdeficient populations may benefit from targeted supplementation under healthcare guidance.
Possible Interactions or Cautions
Excessive preformed vitamin A can lead to hepatotoxicity, teratogenicity, and hypervitaminosis A (symptoms: headache, nausea, skin peeling). High-dose supplementation should be avoided during pregnancy. Betaβcarotene supplements may increase lung cancer risk in smokers.
Final Thoughts
Vitamin A is indispensable for vision, immune defense, and epithelial health. A varied diet typically meets requirements; supplementation should be personalized to avoid deficiency or toxicity.
Scientific Studies
McCollumβ―EV, Simmondsβ―NP. Studies on experimental scurvy. XLI. The necessity of the fatβsoluble A vitamin in the complete diet. J Biol Chem. 1915;22:297β310. PMID:19867818
Sommerβ―A, Westβ―KP Jr. Vitamin A deficiency: health, survival, and vision. Oxford University Press; 1996. https://global.oup.com/academic/product/vitamin-a-deficiency-9780195079979
Sembaβ―RD. Vitamin A and immunity to viral, bacterial and protozoan infections. Proceedings of the Nutrition Society. 1999;58(3):719β727. https://doi.org/10.1017/S0029665199001065