VitaminWell-studiedVitamin

Vitamin A

Half-life

~19–48 days

What is Vitamin A?

Fat-soluble vitamin essential for vision, immune function, and skin health. Stored in the liver; deficiency causes night blindness.

How Vitamin A works

Binds retinoic acid receptors (RARs/RXRs) to regulate gene transcription for vision (rhodopsin synthesis), immune cell differentiation, and skin cell turnover.

Benefits & uses

Vision support
Immune function
Skin health

Common uses: Night vision, immune support, skin health, epithelial tissue maintenance.

Vitamin A dosage

Typical dose: RDA 900 mcg RAE/day (men). Upper limit 3000 mcg. Supplement: 2500–5000 IU/day with food.

Vitamin A half-life

~19–48 days (stored)

Vitamin A side effects

Excess causes hypervitaminosis A: headache, nausea, liver toxicity. Avoid mega-dosing.

Headache and nausea at high doses
Liver toxicity with chronic overdose
Teratogenic — avoid high doses in pregnancy
Bone loss with long-term high-dose use
Well tolerated at RDA

Warnings & monitoring

Fat-soluble — toxic in high chronic doses; avoid high-dose preformed A in pregnancy

Track Vitamin A in Protokol.

Log doses, model half-lives, check interactions, and line it all up against your bloodwork. Free on iPhone and Android.