Vitamin A
Critical for vision, immune function, and skin/mucous-membrane integrity. Easy to get from food; supplement only when there's a real reason.
Strong evidence for vision, immune, and skin in deficient individuals. Less benefit when already replete. Beta-carotene supplementation specifically has shown harm in smokers (CARET, ATBC trials — increased lung cancer risk). Effects on dry eye and skin: 4–8 weeks. Night vision: faster.
Vitamin A covers two related compounds: preformed retinol (from animal foods, directly usable) and provitamin-A carotenoids like beta-carotene (from plants, partially converted in the body). It regulates gene expression in nearly every tissue, supports rod-cell function in the retina, drives epithelial-cell turnover (skin, gut lining, airways), and is essential for T-cell function. Most omnivores get enough from food. Supplementation is for documented deficiency, very-low-fat diets, malabsorption conditions, or specific therapeutic use (acne, immune support).
- Form
- Retinyl palmitate or retinyl acetate for direct vitamin A. Beta-carotene if you prefer plant-derived, but conversion efficiency varies hugely (genetic — some people convert at 20%, others at 2%). Cod liver oil is a natural high-A source (also delivers D and omega-3).
- Dose
- 3,000–10,000 IU/day (900–3,000 mcg RAE). Don't exceed 10,000 IU/day chronically without monitoring — vitamin A is fat-soluble and accumulates.
- Timing
- With a fat-containing meal. AM typical.
- Schedule
- Daily if supplementing. Some protocols use cycled higher-dose pulses for acne or immune support — discuss with a provider.
- Side effects
- Hypervitaminosis A at high chronic doses — headache, dry skin, hair loss, bone pain, liver toxicity. Acute toxicity from single massive doses (e.g. polar bear liver). Beta-carotene at high doses turns skin orange (harmless, reversible).
- Interactions
- Acne-treatment retinoids (isotretinoin) — additive toxicity, do not supplement. Anticoagulants — high-dose vitamin A may potentiate. Methotrexate, tetracyclines — hepatotoxicity risk increases.
- Contraindications
- Pregnancy — preformed vitamin A above 10,000 IU/day is teratogenic. Smokers — avoid beta-carotene supplements (lung cancer risk). Active liver disease.
- Lab markers
- Serum retinol (limited utility — body keeps blood levels stable until severe deficiency). Retinol-binding protein (RBP). For most people, dietary history is more useful than testing.
- Food sources
- Preformed (retinol): liver (especially beef and chicken liver — extremely rich), cod liver oil, egg yolks, dairy fat, butter. Beta-carotene: sweet potato, carrots, pumpkin, butternut squash, dark leafy greens, mango. Eat with fat for absorption.
Pairs with
Vitamin D3 (synergistic nuclear-receptor signalling). Vitamin K2 (the fat-soluble vitamin trio). Zinc (required to mobilise A from liver stores). Dietary fat (absorption).
within Vitamins