What is vitamin D1 found in?

December 19, 2025 •

3 min read

Over 40% of Americans are deficient in vitamin D, often called the 'sunshine vitamin'. Many mistakenly search for specific dietary sources of 'vitamin D1,' unaware that this term is no longer used in modern nutritional science. Instead, the vitamin D family is primarily comprised of D2 and D3, both of which are crucial for human health.

Quick Summary

The term vitamin D1 is an outdated reference to a specific mixture of calciferol, not a distinct vitamin. The nutritionally relevant forms are D2 (ergocalciferol) and D3 (cholecalciferol), found in sunlight, fortified foods, fatty fish, and supplements.

Key Points

Vitamin D1 is not a distinct vitamin: The term is an outdated designation for a mixture of compounds, not a single, pure nutrient found in foods.
Focus on D2 and D3 instead: The two primary, active forms of vitamin D relevant for human health are D2 (ergocalciferol) and D3 (cholecalciferol).
D3 comes from sunlight and animal products: Your skin produces vitamin D3 from sunlight, and it's also found in fatty fish, egg yolks, and fortified dairy.
D2 is found in plants and fortified foods: UV-exposed mushrooms naturally contain D2, while many plant-based milks and cereals are fortified with it.
D3 may be more effective than D2: Some evidence suggests that vitamin D3 is better at raising and maintaining blood vitamin D levels compared to D2.
Supplements are a viable option: For those with limited sun exposure or dietary sources, supplements containing either D2 or D3 can help ensure adequate intake.

The term "vitamin D1" is a historical classification and does not represent a pure, individual vitamin that can be found in a specific food source. It was an early designation for a mixture containing lumisterol and calciferol, which is created by irradiating ergosterol with ultraviolet light. Therefore, the central question, "What is vitamin D1 found in?" is based on a misconception. Modern nutritional science focuses on vitamin D2 and vitamin D3, the primary forms absorbed and utilized by the body.

The True Forms of Vitamin D: D2 and D3

Understanding the actual forms of vitamin D is key to identifying reliable sources. Both D2 (ergocalciferol) and D3 (cholecalciferol) are essential for health, playing crucial roles in calcium absorption, bone health, immune function, and mood regulation. The body can synthesize vitamin D3 from sunlight, while D2 is produced by exposing plant matter to UV light.

Vitamin D2 (Ergocalciferol) Sources

UV-Exposed Mushrooms: This is one of the few natural plant-based sources of vitamin D. Mushrooms, such as portabella and white varieties, produce D2 when exposed to ultraviolet light, much like humans produce D3 from sunlight. The vitamin content can vary significantly based on growing conditions.
Fortified Foods: Many plant-based products, including soy milk, almond milk, and certain cereals, are fortified with vitamin D2. These are excellent options for vegans or those who do not consume animal products.

Vitamin D3 (Cholecalciferol) Sources

Sunlight Exposure: The most direct way to obtain vitamin D3 is through sunlight. When ultraviolet B (UVB) rays hit the skin, a type of cholesterol is converted into vitamin D3. A few minutes of sun exposure several times a week is often sufficient, although this varies depending on skin tone, latitude, and season.
Fatty Fish: Oily fish are some of the best natural food sources of D3. Examples include:
- Salmon
- Sardines
- Mackerel
- Tuna
Fortified Dairy: Many conventional dairy products, such as milk, yogurt, and some cheeses, are fortified with vitamin D3.
Cod Liver Oil: This traditional supplement is a very rich source of vitamin D3.
Egg Yolks: While containing smaller amounts, egg yolks contribute to daily vitamin D intake.

Comparison of Vitamin D2 vs. D3

While both forms are crucial, there are slight differences in how the body processes them. Studies suggest that D3 may be more effective at raising and maintaining overall vitamin D levels in the blood compared to D2. This difference is primarily a matter of efficacy, as both are ultimately converted into the active form of the vitamin by the liver and kidneys.


Feature	Vitamin D2 (Ergocalciferol)	Vitamin D3 (Cholecalciferol)
Primary Source	Plants (e.g., UV-exposed mushrooms), fortified foods	Sunlight exposure, animal products (fatty fish, eggs)
Effectiveness	Effective, but potentially less potent for raising blood levels than D3 over time.	More effective at raising and sustaining blood vitamin D levels in many cases.
Origin	Created via irradiation of ergosterol from yeast or fungi.	Synthesized in skin from sunlight; found naturally in animal fats.
Common In	Vegan supplements, fortified plant-based milk and cereals.	Fish, egg yolks, most multivitamins, animal-derived supplements.
Absorption	Well-absorbed by the body.	Well-absorbed by the body.

Why We Don't Use the Term Vitamin D1 Anymore

The abandonment of the term "vitamin D1" is a testament to scientific advancement. Early research identified calciferol as a substance that cured rickets, but it was later found to be an unpurified mixture rather than a single compound. As researchers refined their understanding, they isolated and named the specific, biologically active forms: D2 and D3. For practical purposes, focusing on getting adequate intake of D2 and D3 from food, sun, or supplements is the correct approach to maintaining healthy vitamin D levels.

Conclusion

In summary, the search for "vitamin D1" sources is a dead end based on outdated terminology. The focus should be on ensuring sufficient intake of either vitamin D2 or D3, which are readily available through several dietary sources and natural sunlight. Whether through sun exposure, fatty fish, fortified cereals, or supplements, maintaining adequate vitamin D is a crucial part of a healthy lifestyle for supporting strong bones, a robust immune system, and overall well-being.

For more detailed nutritional information and daily recommendations, a trusted source like the National Institutes of Health (NIH) is a great resource. NIH Vitamin D Fact Sheet

Frequently Asked Questions

Vitamin D1 is an outdated name for an unpurified mixture, not a true vitamin. The body primarily uses vitamin D2 (from plants and fungi) and vitamin D3 (from sunlight and animal products).

The term is no longer used in contemporary nutritional or medical contexts. It was based on an early, incomplete understanding of vitamin D chemistry.

You can get vitamin D from fatty fish (salmon, tuna), egg yolks, and fortified foods like milk, orange juice, and cereals. UV-exposed mushrooms are a plant-based source.

Both are effective, but studies suggest that vitamin D3 might be more potent at raising blood vitamin D levels and maintaining them for a longer period. The right choice depends on dietary needs and other health factors.

Sunlight is an excellent source of vitamin D3, but factors like skin color, latitude, time of year, and use of sunscreen can limit production. It's recommended to combine sensible sun exposure with dietary sources and, if necessary, supplements.

A deficiency can cause a variety of health issues, including fatigue, bone pain, muscle weakness, and, in severe cases, conditions like rickets in children or osteomalacia in adults.

It depends on the product. Fortified dairy and certain cereals often use D3, while fortified plant-based alternatives like soy milk and almond milk typically use D2.