Is There a Vitamin Called D2? Your Complete Guide to Ergocalciferol

According to the National Institutes of Health, vitamin D exists in two main forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Yes, there is a vitamin called D2, and it plays a crucial role in promoting bone health and supporting immune function, just like its more-commonly discussed counterpart.

Quick Summary

Vitamin D2, or ergocalciferol, is a form of vitamin D found in plants and fungi. Both D2 and D3 effectively raise overall vitamin D levels, though D3 may be more potent at increasing and sustaining levels over time. Key differences lie in their sources, potency, and metabolism.

Key Points

• D2 is Ergocalciferol: The plant-based form of vitamin D, found in fortified foods, mushrooms, and yeast.

• D3 is Cholecalciferol: The animal-based form, produced in the skin from sun exposure and found in fatty fish and eggs.

• D3 is more Potent: Studies show that vitamin D3 is more effective than D2 at increasing and maintaining blood vitamin D levels.

• Sources Differ: D2 is ideal for vegans, while D3 is common in animal products and requires sun exposure for natural production.

• Both Treat Deficiency: Both D2 and D3 are used clinically to treat vitamin D deficiency, though dosage and efficacy can vary.

• Supports Key Functions: Both forms aid in calcium absorption for bone health and support immune system function.

What Exactly is Vitamin D2 (Ergocalciferol)?

Yes, the vitamin D family includes two major forms: ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Vitamin D2 is a fat-soluble vitamin primarily sourced from plants and fungi, such as mushrooms and yeast, often when they are exposed to ultraviolet (UV) light. This makes it a key source of vitamin D for individuals on vegetarian or vegan diets. The other form, vitamin D3, is synthesized in animal skin upon sun exposure and is found in animal-based foods like fatty fish and egg yolks. For many years, both D2 and D3 were considered interchangeable for treating vitamin D deficiency, but more recent research has shed light on their subtle yet important differences.

Sources of Vitamin D2 vs. Vitamin D3

The primary difference between vitamin D2 and vitamin D3 lies in their origins and, subsequently, their primary food sources. Understanding where each comes from is essential for those with specific dietary needs, such as vegans or vegetarians who rely on plant-based nutrients. Here is a quick breakdown of their sources:

Vitamin D2 Sources

• Mushrooms: Exposing certain types of mushrooms (like portobello or maitake) to UV light significantly boosts their natural vitamin D2 content.
• Yeast: Some yeasts, after UV irradiation, produce vitamin D2.
• Fortified Foods: Many manufacturers use vitamin D2 to fortify plant-based milk alternatives (like oat, soy, and almond milk), cereals, and some orange juices.
• Supplements: Vitamin D2 supplements are widely available in various forms, including capsules, tablets, and liquids.

Vitamin D3 Sources

• Sun Exposure: The human body naturally produces vitamin D3 when the skin is exposed to UVB radiation from the sun.
• Fatty Fish: Excellent dietary sources include salmon, mackerel, and sardines.
• Egg Yolks: A modest source of vitamin D3.
• Fortified Milk and Dairy: Cow's milk is often fortified with vitamin D3, as are some yogurts.
• Supplements: Vitamin D3 supplements are commonly derived from lanolin (sheep's wool). Vegan-friendly D3 derived from lichen is also available.

Comparing Potency and Efficacy: D2 vs. D3

Early research suggested that vitamin D2 and D3 were equally effective in treating rickets, but modern studies using more precise measurement methods (like serum 25-hydroxyvitamin D levels) tell a different story. The consensus from a growing body of evidence indicates that vitamin D3 is more potent and effective at raising and maintaining vitamin D levels in the blood. This difference is largely due to how the body metabolizes each form.

What happens in the body?

Both D2 and D3 are converted in the liver to 25-hydroxyvitamin D (calcifediol), which is the main circulating form of the vitamin. However, the liver's enzymes appear to metabolize D3 more efficiently. Furthermore, vitamin D2 may bind less effectively to the vitamin D binding protein (DBP) in the blood, potentially contributing to its lower overall efficacy and shorter duration of action. Some studies have also pointed to potential stability issues with D2 supplements compared to D3.

Understanding Clinical Use and Recommendations

Despite the differences in potency, both vitamin D2 and vitamin D3 are used clinically to prevent and treat vitamin D deficiency. The choice between them can depend on a variety of factors, including dietary restrictions and availability. High-dose prescriptions, for example, are often available only as vitamin D2, but a healthcare provider will determine the appropriate dosage to effectively raise a patient's levels, regardless of the form. The ultimate goal is to restore adequate vitamin D status, which is crucial for a wide range of bodily functions.

Key Functions of Vitamin D (Both D2 and D3)

• Calcium Absorption: Both forms play a critical role in helping the body absorb calcium, which is essential for strong bones and teeth.
• Immune Function: Vitamin D supports a healthy immune system and helps modulate the body's immune responses.
• Muscle Function: Adequate vitamin D levels are important for proper muscle function.
• Cell Growth and Metabolism: It helps regulate cell growth, neuromuscular function, and glucose metabolism.

Comparison Table: Vitamin D2 vs. Vitamin D3

Feature	Vitamin D2 (Ergocalciferol)	Vitamin D3 (Cholecalciferol)
Primary Source	Plants and fungi (e.g., mushrooms and yeast).	Animals (e.g., fatty fish, egg yolks, liver), and produced by skin exposed to sunlight.
Effectiveness	Considered less potent and effective at raising serum vitamin D levels.	More potent and effective at raising and sustaining serum vitamin D levels.
Stability	May be more sensitive to temperature and humidity, potentially leading to a shorter shelf life.	Generally more stable, making it a reliable option for supplements and fortification.
Dietary Suitability	Excellent for vegans and vegetarians.	Primary sources are animal-based; vegan versions derived from lichen are available.
Metabolism	Less efficiently converted by the liver and may bind less effectively to transport proteins.	More efficiently processed by the body into its active form.
Fortified Foods	Commonly used to fortify plant-based milks and cereals.	Often used to fortify dairy milk and some other products.

Conclusion

In conclusion, there is indeed a vitamin called D2, also known as ergocalciferol. While it functions similarly to vitamin D3 in the body, primarily by aiding in calcium absorption for bone health, research consistently shows that vitamin D3 is more effective at raising and maintaining vitamin D levels. This difference is tied to their respective sources—D2 from plants and D3 from animals or sunlight—and how the body metabolizes them. Both forms are used therapeutically for vitamin D deficiency, and the best choice often depends on an individual's dietary preferences, specific health needs, and a doctor's recommendation. Understanding these distinctions allows for more informed decisions about supplementation and dietary sources to ensure optimal vitamin D status. For those with plant-based diets, vitamin D2 from fortified foods and mushrooms remains a vital option, but awareness of its potential lower potency compared to D3 is beneficial. You can find more comprehensive details on nutrient functions on the official website of the National Institutes of Health.

Frequently Asked Questions

Is vitamin D2 an actual vitamin?

Yes, vitamin D2 is a legitimate and recognized form of vitamin D, also known as ergocalciferol. It plays the same fundamental role in the body as vitamin D3, helping with calcium absorption and bone health.

What is the primary source of vitamin D2?

The primary sources of vitamin D2 are plants and fungi. It is produced when ergosterol in these organisms is exposed to ultraviolet (UV) light. It is also commonly used to fortify foods like cereals and plant-based milks.

Is vitamin D2 or D3 better for you?

While both vitamins raise blood vitamin D levels, research generally suggests that vitamin D3 is more effective at doing so and maintaining those levels for a longer period. However, both can be used to treat deficiency.

Can vegans get enough vitamin D2?

Yes, vegans can get enough vitamin D by consuming foods fortified with vitamin D2, such as some plant-based milks and cereals, and by eating UV-light-exposed mushrooms. Vegan-sourced D3 from lichen is also available in supplements.

How is vitamin D2 different from D3 structurally?

Structurally, vitamin D2 differs from D3 in its side chain. D2 has an additional double bond and a methyl group, which is a key reason for the difference in how the body metabolizes them.

Do you need a prescription for vitamin D2?

Prescription-strength doses of vitamin D2 (often 50,000 IU) are available, while lower-dose vitamin D2 and many forms of vitamin D3 are available over the counter. A doctor can determine if a prescription is necessary for your specific needs.

Why do some fortified foods contain D2 instead of D3?

Vitamin D2 is generally less expensive to produce than D3. Additionally, using D2 derived from plant-based sources allows manufacturers to label products as vegan-friendly.