Understanding Vitamin A Through a Root Cause Lens
Vitamin A has become one of the most misunderstood nutrients in modern nutrition. Most people know it supports vision and immune health, but far fewer understand that the form and context of vitamin A matter significantly.
From a Root Cause Protocol perspective, vitamin A is not simply a nutrient measured in international units. It functions within a broader metabolic system involving retinol-binding proteins, copper-dependent enzymes, iron recycling, and mitochondrial signaling.
One of the most important distinctions is between retinol naturally present in cod liver oil and isolated vitamin A compounds such as retinyl palmitate commonly used in fortified foods and supplements.
Understanding this difference helps explain why traditional diets relied heavily on foods like liver and cod liver oil rather than isolated vitamins.
Vitamin A in Nature: Retinol from Cod Liver Oil
Cod liver oil has long been recognized as one of the most concentrated whole-food sources of vitamin A. In fish liver oils, vitamin A occurs primarily as retinyl esters that are converted to retinol during digestion before absorption.¹
Unlike isolated vitamin A supplements, cod liver oil delivers vitamin A within a lipid matrix that also includes omega-3 fatty acids and naturally occurring fat-soluble nutrients. These lipids play a crucial role in the absorption and transport of vitamin A through chylomicrons following digestion.²
This nutritional context matters because fat-soluble vitamins are metabolically dependent on dietary lipids for efficient absorption and transport.
Once absorbed, retinol enters circulation bound to retinol-binding protein (RBP), which delivers vitamin A from the liver to tissues throughout the body.³
This transport system tightly regulates vitamin A availability so tissues receive what they need without large fluctuations in circulating retinoids.
Retinyl Palmitate: The Isolated Form of Vitamin A
Retinyl palmitate is a synthetic retinyl ester commonly used in:
• multivitamins
• fortified dairy products
• infant formula
• processed foods
Chemically, retinyl palmitate is simply retinol esterified with palmitic acid, which improves shelf stability and manufacturing consistency.⁴
From a metabolic standpoint, retinyl palmitate must undergo the same first step as naturally occurring retinyl esters: enzymatic hydrolysis in the intestine to release retinol prior to absorption.¹
In other words, the body ultimately handles both forms through similar biochemical pathways once absorbed.
However, the source and accompanying nutrient matrix may influence downstream retinoid metabolism.
Whole-Food Sources May Influence Retinoid Signaling
A controlled human study compared vitamin A metabolism after consuming liver paste (a whole-food vitamin A source) versus a retinyl palmitate supplement.
Researchers observed that although overall vitamin A absorption was comparable, plasma retinoic acid metabolites were significantly higher after consumption of liver compared with the supplement form.⁵
Retinoic acid is the active signaling molecule derived from retinol that regulates gene expression, immune signaling, and cellular differentiation.
These findings suggest that whole-food vitamin A sources may influence retinoid signaling differently than isolated vitamin A compounds, likely due to the broader nutrient matrix present in foods like liver and fish liver oils.
Vitamin A Transport and Retinol-Binding Protein
Vitamin A metabolism depends on a tightly regulated transport system centered around retinol-binding protein (RBP).
After vitamin A is absorbed and stored in the liver, retinol is released into circulation bound to RBP, which delivers it to tissues where it is required.³
This transport system is sensitive to metabolic conditions. Research shows that:
• inflammation and infection reduce circulating retinol by lowering RBP production
• liver health influences vitamin A storage and mobilization
• nutrient status affects retinoid transport dynamics⁶
From a Root Cause perspective, vitamin A metabolism intersects with mineral physiology, particularly copper-dependent proteins involved in oxidative balance and iron regulation.
Vitamin A and Iron Metabolism
Vitamin A plays an important role in iron metabolism and red blood cell production.
Research has shown that vitamin A status influences hemoglobin synthesis and the mobilization of stored iron from tissues.⁶
This interaction helps explain why nutrient-dense animal foods historically played a central role in traditional diets. Many of these foods contain vitamin A alongside minerals and fat-soluble cofactors that support metabolic balance.
From a physiological perspective, vitamin A contributes to a broader system involving:
• iron recycling
• immune signaling
• cellular energy metabolism
• oxidative stress regulation
Why Traditional Diets Used Cod Liver Oil
Long before vitamin A was identified as a nutrient, cod liver oil was widely used in traditional cultures.
This makes sense from a biochemical standpoint. Cod liver oil naturally provides:
• preformed vitamin A (retinol)
• vitamin D
• long-chain omega-3 fatty acids (EPA and DHA)
These nutrients support immune function, metabolic signaling, and tissue repair.
Unlike many modern supplements that isolate nutrients, cod liver oil provides these compounds in their naturally occurring balance.
Choosing a High-Quality Cod Liver Oil
Not all cod liver oils are produced the same way. Processing methods, sourcing, and vitamin fortification practices can significantly affect the final product.
Traditionally produced cod liver oil provides vitamin A in the form of naturally occurring retinyl esters alongside omega-3 fatty acids and vitamin D.
Because fat-soluble nutrients rely on lipid transport systems for absorption and metabolism, preserving this natural nutrient matrix is important.
For those looking for a carefully sourced option, Cod Liver IQ from Formula IQ is derived from wild-caught Icelandic cod and produced with the goal of maintaining vitamin A and vitamin D in their naturally occurring forms rather than relying on synthetic vitamin fortification.
You can learn more about it here:
https://formulaiq.com/products/cod-liver-iq
When evaluating cod liver oil products, important considerations include:
• sourcing and purity of the fish oil
• processing methods that protect fat-soluble nutrients
• avoiding synthetic vitamin fortification
• maintaining the natural balance of vitamins A and D
These factors help preserve the nutritional characteristics that historically made cod liver oil a staple food.
Final Thoughts
Vitamin A metabolism is more complex than simply measuring intake.
Both cod liver oil and retinyl palmitate ultimately provide vitamin A to the body, but the source and nutritional context can influence how vitamin A behaves metabolically.
Whole-food sources like cod liver oil deliver vitamin A within a broader nutrient matrix that includes lipids and complementary fat-soluble nutrients.
Isolated compounds such as retinyl palmitate provide the vitamin alone without that context.
From a traditional nutrition perspective, this helps explain why nutrient-dense foods such as liver and fish liver oils have remained foundational dietary sources of vitamin A for generations.
References
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Penniston KL, Tanumihardjo SA. The acute and chronic toxic effects of vitamin A. American Journal of Clinical Nutrition. 2006.
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Reboul E. Absorption of vitamin A and carotenoids by the enterocyte: focus on transport proteins. Nutrients. 2013.
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Bellovino D et al. Retinol-binding protein and vitamin A transport. Biochimica et Biophysica Acta. 2003.
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Carazo A et al. Vitamin A: Forms, sources, kinetics and detection. Nutrients. 2021.
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Van Vliet T et al. Plasma retinoic acid metabolites are higher after intake of liver paste compared with vitamin A supplements. Journal of Nutrition. 2001.
- Tanumihardjo SA et al. Biomarkers of nutrition for development: vitamin A review. Journal of Nutrition. 2016.
