Vitamin A: Why It Matters, Why Plants Don’t Provide It, and Why Liver Still Reigns Supreme

Vitamin A is not optional biology

Vitamin A is an essential fat-soluble nutrient required for vision, immune regulation, hormone signaling, skin and gut integrity, and cellular differentiation. Unlike many nutrients that can be substituted or partially compensated for, vitamin A has specific biochemical roles that cannot be fulfilled by other compounds. When vitamin A is insufficient or poorly utilized, the body does not adapt gracefully — it degrades.

Vitamin A is not found in plants

This is one of the most misunderstood points in nutrition.

Plants do not contain vitamin A.They contain carotenoids (such as beta-carotene), which are vitamin A precursors that must be converted into retinol by the human body.

That conversion:

• Is genetically variable

• Requires adequate zinc, thyroid hormone, bile flow, and metabolic health

• Is down-regulated by inflammation and insulin resistance

In real humans, conversion efficiency ranges widely and can be poor or negligible in a large percentage of the population. This is why someone can eat plenty of vegetables, have high beta-carotene levels, and still show signs of functional vitamin A deficiency.

What vitamin A actually does in the body

Vitamin A (retinol and its active metabolites) is involved in:

• VisionRetinol is required to form rhodopsin, the light-sensitive pigment in the retina. Without it, night vision, dark adaptation, and visual clarity decline.

• Immune balanceVitamin A regulates immune responses, helping prevent both immune suppression and over-activation.

• Epithelial integrityIt maintains the lining of the gut, lungs, and skin — a key defense against chronic inflammation and endotoxin leakage.

• Hormonal and metabolic signalingVitamin A interacts with nuclear receptors that influence insulin sensitivity, fat cell behavior, and cellular differentiation.

This is not a “nice to have” vitamin — it is foundational.

Why the eyes are especially sensitive

The eyes are among the highest vitamin-A-demand tissues in the body. Early or subclinical deficiency often shows up as:

• Poor night vision

• Dry or irritated eyes

• Light sensitivity

• Slower dark adaptation

Importantly, these symptoms can appear long before standard blood tests flag a deficiency, especially in people with metabolic dysfunction.

Why liver is the single best source

Liver is unique because it provides:

• Pre-formed vitamin A (retinol) — no conversion required

• Zinc, needed to transport vitamin A to the retina

• B12, folate, and choline, supporting nerve function, methylation, and liver health

• Exceptional bioavailability

This combination is why liver works where plant sources often fail. It delivers vitamin A in the form the body actually uses, alongside the cofactors required for that vitamin to function properly.

You do not need large amounts:

• ~15–30 g once or twice per week is sufficient for most people
  

  

Useful alternative sources (supportive, not replacements)

While liver is unmatched, these foods can support vitamin A status:

• Egg yolks – provide small amounts of retinol plus lutein and zeaxanthin for macular protection

• Fish roe (caviar) – rich in DHA for retinal structure and modest retinol

• Grass-fed butter or ghee – low-dose retinol and fat to support absorption

• Full-fat dairy (from pastured animals) – minor retinol contribution

Leafy greens and colorful vegetables provide carotenoids, which are useful antioxidants, but they do not replace retinol, especially in people with insulin resistance or inflammation.

A critical modern problem: intake vs utilization

Many people today do not suffer from a lack of vitamin A intake — they suffer from poor utilization.

Insulin resistance, chronic inflammation, low bile flow, and gut dysfunction can all impair:

• Conversion of carotenoids

• Transport of retinol

• Delivery to high-demand tissues like the eyes

This is why vitamin A deficiency can exist despite a “healthy diet.” Vitamin A is a designed requirement of the human body, not a dietary trend. The human visual system, immune system, and epithelial tissues are built to function using pre-formed vitamin A (retinol), which is required for processes such as rhodopsin formation in the retina and proper immune regulation. Plant foods do not supply vitamin A itself, only precursor compounds that require multiple enzymatic steps and adequate metabolic health to convert. When these systems are compromised — as is common today — reliance on precursors alone becomes insufficient. Foods that provide vitamin A in its usable form, particularly liver, align with how the human body is structured to receive and utilize this nutrient.