Vitamin A — Supplements
Fat-soluble vitamin essential for vision, immune function, and cellular differentiation.
Overview
Vitamin A encompasses retinoids (preformed vitamin A: retinol, retinal, retinoic acid) and provitamin A carotenoids (beta-carotene). Retinoids are essential for rhodopsin synthesis (night vision), immune cell differentiation, gene expression regulation, and epithelial barrier maintenance. Vitamin A deficiency is the leading cause of preventable childhood blindness worldwide. In developed countries, supplementation is primarily used for immune support, skin health, and preventing deficiency in at-risk populations (malabsorption, liver disease, strict vegan diets).
Indications
- Immune function support
- Vision health and night vision
- Skin and epithelial integrity
- Deficiency prevention in at-risk populations
Mechanism of Action
Retinoic acid binds to nuclear retinoic acid receptors (RAR/RXR) that regulate gene transcription for cell differentiation
Dosing
| Compound | Dose | Frequency | Notes |
|---|---|---|---|
| Vitamin A (as retinyl palmitate) | 5,000 IU (1,500 mcg RAE) | Once daily | Take with fat-containing meal; do not exceed 10,000 IU/day unless medically supervised |
Safety & Contraindications
- Teratogenic: absolute contraindication in pregnancy at doses >10,000 IU/day
- Hepatotoxic at chronic high doses (>25,000 IU/day)
- Hypervitaminosis A: headache, nausea, peeling skin, bone pain, liver damage
- Smokers should avoid high-dose beta-carotene supplements (increased lung cancer risk per ATBC trial)
- UL: 10,000 IU/day (3,000 mcg RAE) for adults