← Nutrients · Metabolic Health

Vitamin A (Retinol / Carotenoids)

VitaminFoundationalHormonal

Controls how cells specialize, and lets your eyes see in dim light.

At a glance

Essential
Strong human evidence

How to take it

  • 700–900 mcg a day
  • Liver is the richest source. Also eggs, dairy, carrots, sweet potato.

Watch out

  • Carotenoids in plants convert to vitamin A less reliably than retinol from animal foods

Signs you're low

  • Night blindness
  • Dry eyes and skin
  • More infections
The Research

Mechanisms, studies and evidence grades for each claim above.

Functions

Gene regulation (retinoic acid). Retinoic acid binds RAR/RXR receptors, regulating transcription of differentiation genes and controlling epithelial cell identity and tissue development.1

Vision (retinal cycle). 11-cis-retinal combines with opsin to form rhodopsin, the photoreceptor complex; light-induced isomerization initiates visual signal transduction.2

Epithelial integrity. Maintains differentiation of epithelial tissues (skin, gut, respiratory tract) and prevents keratinization and barrier dysfunction.3

Immune modulation. Regulates immune cell differentiation and mucosal immunity, supporting barrier-mediated immune defense.3

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Intake

Roughly 700–900 µg/day.

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Deficiency effects

Night blindness; impaired epithelial integrity (dry eyes/skin, barrier dysfunction); immune dysfunction and higher infection risk.

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Top foods

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Key insight

Vitamin A controls cell identity — through gene regulation and light sensing, it determines how tissues differentiate and respond to the environment.

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References

  1. Blomhoff R, Blomhoff HK. Overview of retinoid metabolism and function. J Neurobiol. 2006.
  2. Saari JC. The retinoid visual cycle. Prog Retin Eye Res. 2012.
  3. Sommer A. Vitamin A deficiency and clinical disease. J Nutr. 2008.