Vitamin A

What It Is

“Vitamin A” is a fat-soluble essential nutrient that exists in two main forms:

1. Preformed vitamin A (retinoids) — found in animal-derived foods (liver, egg yolks, dairy, cod liver oil) and also used in supplements and medical formulations (retinol, retinal, retinoic acid).
2. Provitamin A carotenoids — plant-derived pigments (e.g. beta-carotene in carrots, sweet potatoes, dark leafy greens) that the body converts to active vitamin A.

Because it is fat-soluble, vitamin A is absorbed with dietary fat and stored mainly in the liver.

How It Works

Vitamin A is not just a “nutrient” — it functions like a hormone-like signaling molecule and gene-expression regulator.

• Vision — Retinal (a form of vitamin A) binds to opsins in the retina to form rhodopsin, which is essential for seeing in low light.

• Epithelial integrity — Retinoic acid regulates gene transcription in skin, gut lining, lungs, and urogenital tract to maintain barrier function against infections.

• Immune modulation — Retinoids influence differentiation of immune cells (T-cells, B-cells) and antibody production; they tune—not merely stimulate—immune response.

• Development and growth — In pregnancy and early childhood, vitamin A governs cellular differentiation and organ formation (especially eye, lung, and heart).

• Antioxidant defense (for carotenoids) — Carotenoids quench free radicals and reduce oxidative stress.

Why It’s Important

• Prevents night blindness and xerophthalmia — without sufficient vitamin A, eyes cannot adapt to darkness and the cornea can develop keratinization leading to irreversible blindness.

• Maintains skin and mucosal barrier — lowers risk of respiratory, gastrointestinal, and genitourinary infections by preserving epithelial defenses.

• Supports immune competence — deficiency is strongly associated with increased morbidity and mortality from infectious diseases, especially in children.

• Critical in pregnancy and early life — both deficiency and excess have profound developmental consequences.

• Supports skin health — topical and systemic retinoids are foundational in dermatology for acne, photo-aging, and dysplasia because of their regulatory effect on cell turnover and gene expression.

Considerations

• Deficiency — Common in low-resource settings, strict low-fat dieters, malabsorption (celiac, IBD, pancreatic insufficiency), chronic alcoholism, and those with liver disease. Signs progress from night blindness to xerosis, frequent infections, and in advanced cases corneal ulceration.

• Toxicity — Because it is stored, preformed vitamin A can accumulate. Excess causes liver injury, bone loss, intracranial hypertension, teratogenicity (in pregnancy), dry/peeling skin, headaches, and nausea. Carotenoids do not generally cause toxicity but may cause benign skin yellowing (carotenodermia).

• Pregnancy — Strict upper limits apply to preformed vitamin A; excess is teratogenic. Prenatal vitamins are formulated with safety margins for this reason.

• Liver health — Preformed vitamin A overload stresses the liver; caution with existing liver disease or chronic alcohol use.

• Form matters — Retinoids have pharmacologic potency; carotenoids depend on conversion capacity, which varies by genetics, zinc status, thyroid function, and gut health.

• Fat absorption dependency — Very low-fat diets or fat malabsorption impair uptake of both retinoids and carotenoids.

• Drug interactions — Retinoids interact with other hepatotoxic agents and are contraindicated with systemic retinoid prescriptions (e.g. isotretinoin) due to additive toxicity.