Is Vitamin D Made From Fish Oil? Separating Myth from Fact

December 8, 2025 •

4 min read

While fish oil is a well-known source of vitamin D, the vitamin itself is not created from the oil; rather, it is a fat-soluble compound naturally present in the fatty tissues and livers of fish.

Quick Summary

Fish do not produce vitamin D from their oil; instead, they naturally contain it in their fat and livers. Most commercial vitamin D supplements are derived from different sources.

Key Points

Natural Presence: Vitamin D is naturally present in the tissues and liver oil of fatty fish, not chemically manufactured from the oil itself.
Sunlight Activation: Fish, like humans, produce vitamin D3 in response to sunlight exposure, which is then stored in their fatty tissues.
Supplement Sources: Commercial vitamin D supplements often use different starting materials, such as lanolin (sheep's wool) for D3 or irradiated yeast for D2.
Source Variation: The amount of vitamin D in fish can vary widely, influenced by factors like diet and whether they are wild or farmed.
Oil Type Matters: Traditional cod liver oil contains vitamin D, whereas modern, highly refined fish oil supplements may have the vitamin removed during processing unless it is added back.
Different Nutrients: Fish oil primarily contains omega-3 fatty acids, which are distinct from the fat-soluble vitamin D, though both are important for health.

The Difference Between Naturally Occurring and Manufactured Vitamin D

It is a common misconception that fish oil is the source material for manufacturing vitamin D supplements. The truth is more nuanced. Fatty fish, such as salmon, tuna, and mackerel, are among the best natural dietary sources of vitamin D3. The vitamin is present in their fatty tissues and liver. When you consume these foods, or traditional cod liver oil derived directly from the fish's liver, you are getting the vitamin D that the fish naturally accumulated during its life. In contrast, a significant portion of commercial vitamin D supplements is manufactured using other starting materials.

For example, vitamin D2 (ergocalciferol) is produced by irradiating yeast with ultraviolet (UV) light. Vitamin D3 (cholecalciferol) supplements, which are more widely used, are often manufactured by irradiating lanolin, a wax obtained from sheep's wool, with UV light. There are also animal-free versions of vitamin D3, such as those derived from lichen. The key takeaway is that the vitamin D found in fish oil is a naturally occurring nutrient, while the vitamin D in many supplements is synthesized in a lab using non-fish sources.

The Role of Sunlight in Vitamin D Production

For both humans and fish, the primary mechanism for producing vitamin D3 is through exposure to ultraviolet B (UVB) radiation from sunlight. In humans, this process involves the conversion of a compound called 7-dehydrocholesterol in the skin into pre-vitamin D3. Fish and other marine organisms also possess this ability. The vitamin D3 that they produce is then stored in their fatty tissues and liver, which is why consuming fatty fish is an effective way for humans to obtain dietary vitamin D. This natural sunlight-based production system is fundamentally different from the industrial manufacturing process used for many supplements.

Fish Oil vs. Cod Liver Oil: An Important Distinction

To understand the different vitamin D content, it's essential to distinguish between standard fish oil and cod liver oil.

Cod Liver Oil: This oil is extracted specifically from the livers of cod. It is historically known for being a rich source of both omega-3 fatty acids and naturally occurring vitamins A and D. Traditional formulations of cod liver oil contain the natural vitamin D3 that was present in the fish's liver.
Modern Refined Fish Oil Supplements: Many contemporary fish oil supplements are highly processed and purified to concentrate the omega-3s and remove other compounds. During this process, the naturally occurring vitamin D might be filtered out or destroyed. If vitamin D is included, it is often added back into the final product as a separate ingredient, derived from sources like lanolin, not from the fish oil itself.

Beyond Fish: Other Sources of Vitamin D

While fish is a potent source, it is not the only way to get this vital nutrient. Here is a list of other sources:

Other Natural Food Sources:
- Beef liver
- Egg yolks
- Cheese
- Certain wild mushrooms that have been exposed to sunlight (providing D2)
Fortified Foods:
- Milk and some milk alternatives
- Certain breakfast cereals
- Some yogurts and orange juices

The Wild vs. Farmed Fish Debate

The vitamin D content in fish can vary widely depending on the species and its diet. A study showed that farmed salmon contained significantly less vitamin D than wild salmon. This is because wild fish have more exposure to natural sunlight and often consume a different diet than their farmed counterparts, which affects the amount of vitamin D they accumulate and store. Therefore, relying on food charts can be misleading, and understanding the source of your fish is crucial if you're counting on it for a reliable vitamin D intake.

A Comparison of Vitamin D Sources


Source Type	Vitamin D Form	Omega-3s	Manufacturing Process	Typical Concentration
Natural Fish (Fatty)	D3	Yes	Natural accumulation from diet/sunlight	Varies widely
Cod Liver Oil (Traditional)	D3	Yes	Extracted directly from fish liver	Contains natural D, but can vary
Fish Oil Supplement (Refined)	D3 (Added)	Yes (High)	Processed for omega-3s, D often added back	Standardized, but not naturally from oil
Vitamin D3 Supplement (Lanolin)	D3	No	UV irradiation of lanolin from sheep's wool	Standardized, high dose
Vitamin D2 Supplement (Yeast)	D2	No	UV irradiation of ergosterol in yeast	Standardized, but less potent than D3

Conclusion

In summary, the notion that vitamin D is chemically made from fish oil is inaccurate. Rather, fatty fish and their livers, including the oil extracted from them, are natural dietary sources because they have accumulated vitamin D3 in their bodies. The manufacturing processes for most dietary vitamin D supplements rely on entirely different source materials, such as lanolin or yeast. So, while fish oil can certainly contribute to your vitamin D intake, it is the fish itself that is the original source, not the manufacturing process of the oil. This distinction is crucial for understanding your nutritional intake, especially if you rely on supplements.

To learn more about vitamin D and its various forms, consult authoritative resources like the National Institutes of Health Fact Sheet.

Frequently Asked Questions

No, not all fish oil supplements contain vitamin D. Highly refined fish oil, which is processed to concentrate omega-3s, may have the natural vitamin D removed unless it is specifically added back during manufacturing.

The vitamin D in traditional cod liver oil is natural, meaning it is derived from the cod's liver itself. Cod liver oil is known to contain naturally occurring vitamins A and D.

Fish, particularly fatty species, produce vitamin D in their skin in response to sunlight exposure, similar to how humans do. This vitamin is then stored in their fat and liver.

The vitamin D in fish oil is naturally occurring within the fish's fat. A supplement from lanolin is manufactured by irradiating sheep's wool wax with UV light to create vitamin D3.

Yes, vegetarian sources include some mushrooms (which provide D2 when exposed to UV light) and fortified foods like milk alternatives and cereals. There are also vegan D3 supplements derived from lichen.

No, they are different. Fish oil is a general term, typically referring to oil from the flesh of various fish. Cod liver oil is specifically from the liver of cod and naturally contains both vitamin A and D.

You should check the product label for the source. Most supplements explicitly state their origin, whether from lanolin, lichen, or if it is from a fish oil base. Fish oil-based supplements will often list omega-3s as a primary ingredient.