How much vitamin D2 equals D3? Unpacking the Potency and Equivalence

October 30, 2025 •

4 min read

Contrary to past assumptions, studies indicate that vitamin D3 is significantly more effective than vitamin D2 at raising and maintaining vitamin D levels in the blood. This raises a critical question for many supplement users: How much vitamin D2 equals D3 when considering biological potency and effectiveness?

Quick Summary

Comparing vitamin D2 and D3 reveals significant potency differences, with D3 proving more effective for raising serum levels. Factors like metabolism influence this disparity, making a simple 1:1 conversion inaccurate for achieving equivalent biological effects.

Key Points

Superior Potency: Vitamin D3 is significantly more potent than vitamin D2, with studies suggesting it can be nearly twice as effective at raising serum vitamin D levels.
Metabolic Differences: The body metabolizes vitamin D2 less efficiently than D3, and its active metabolite is cleared from the bloodstream more quickly.
Source Variation: Vitamin D2 is derived from plants and fungi, while D3 comes from animals and is produced by the skin upon sun exposure.
Inaccurate 1:1 Conversion: Do not assume a 1:1 equivalence between D2 and D3 for the same biological effect, especially when addressing a deficiency, as D3 provides a higher, more sustained increase.
Factors Influencing Potency: The difference in effectiveness can be influenced by factors like baseline vitamin D levels, dosing frequency, and body mass index.
Clinical Preference: Vitamin D3 is generally the preferred form for supplementation due to its higher and longer-lasting effect, although D2 is a suitable option for vegans when potency differences are considered.

Disclaimer

Information provided in this article is for general knowledge purposes only and does not constitute medical advice. Always consult with a healthcare professional before starting any new supplement regimen or making changes to your current one.

What Are Vitamin D2 and D3?

Vitamin D is a crucial fat-soluble vitamin necessary for bone health, immune function, and calcium absorption. It exists in two main forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). These forms have similar functions but differ in sources, metabolism, and potency.

Vitamin D2 (Ergocalciferol): Found in fungi and fortified foods like cereals and plant-based milks. It's also available in supplements.
Vitamin D3 (Cholecalciferol): Produced in the skin upon sun exposure and present in animal products like fatty fish and egg yolks. This form is commonly used in supplements.

The Unequal Efficacy: Why D3 is More Potent

Both D2 and D3 are converted to the active form, calcitriol, in the liver and kidneys. However, D3 consistently demonstrates greater efficacy in raising and sustaining total serum 25-hydroxyvitamin D [25(OH)D] levels. A study in The Journal of Clinical Endocrinology & Metabolism indicated D3 was about 87% more potent than D2. A meta-analysis also supported D3's superiority, especially with large, infrequent doses. The reasons for this difference are rooted in metabolism:

Metabolite Differences: D2 is converted to 25-hydroxyvitamin D2 and D3 to 25-hydroxyvitamin D3.
Faster D2 Clearance: Evidence suggests that 25(OH)D2 is cleared from the bloodstream faster than 25(OH)D3 due to lower binding affinity to the vitamin D binding protein. This leads to a shorter effect for D2.
Potential Suppressive Effect: Some research indicates high-dose D2 might even suppress the body's natural 25(OH)D3 production.

Is There a Simple Conversion Formula for How much vitamin D2 equals D3?

Due to the potency difference, a simple 1:1 conversion based on international units (IU) is not clinically accurate for achieving the same biological effect. Direct comparisons from studies provide a clearer picture. For instance, achieving a similar effect as a certain amount of D3 may require a higher amount of D2. Conversely, a specific amount of D2 may be roughly equivalent to a lower amount of D3 in terms of increasing serum levels. The precise equivalence can vary based on individual factors like vitamin D status, dosing frequency, and BMI. For correcting a diagnosed deficiency, healthcare providers often recommend D3 due to its greater efficacy, with a specific regimen tailored to the individual.

Comparison Table: Vitamin D2 vs. Vitamin D3


Factor	Vitamin D2 (Ergocalciferol)	Vitamin D3 (Cholecalciferol)
Primary Source	Plants, fungi (mushrooms), and fortified foods like some cereals and plant-based milks.	Sunlight exposure, animal products (fatty fish, egg yolks), and most supplements.
Biological Potency	Less potent in raising and maintaining total serum 25(OH)D levels in the blood.	More potent and effective, especially for raising and sustaining vitamin D status.
Metabolism	Metabolized into 25(OH)D2, which is cleared from the blood more quickly than its D3 counterpart.	Metabolized into 25(OH)D3, which binds more effectively to the transport protein and lasts longer in circulation.
Best For	Vegans or those with plant-based diets who want a supplement from a non-animal source.	Correcting and preventing deficiencies in most populations, and is often the preferred choice by clinicians.
Effectiveness	Lower efficacy, particularly with bolus (infrequent, high-dose) regimens compared to daily dosing.	Higher and more sustained increase in vitamin D levels, regardless of daily or intermittent dosing strategy.

What This Means for Your Diet and Supplements

For most individuals aiming to optimize their vitamin D status, including those with a deficiency, vitamin D3 is often the preferred option due to its higher potency and sustained effects. However, D2 serves as a suitable alternative for vegans or vegetarians seeking a plant-based supplement. It's crucial for individuals using D2 to be aware of the potency differences and work with a healthcare provider to determine appropriate intake amounts.

When selecting a supplement, check the label for the form of vitamin D. Include fatty fish and other animal products for D3 or UV-exposed mushrooms for D2 in your diet. Sensible sun exposure also effectively promotes natural D3 production. For further information, the NIH Office of Dietary Supplements is a valuable resource.

Conclusion

While a precise, universal answer to 'how much vitamin D2 equals D3' is not feasible due to metabolic and individual variances, scientific evidence indicates that vitamin D3 is generally the more potent form for increasing blood vitamin D levels. For addressing a deficiency, D3 supplementation is often preferred for faster, more lasting results. Nevertheless, both D2 and D3 contribute to vitamin D status and can be used effectively with appropriate medical guidance and consideration of potency differences, particularly for individuals following a plant-based diet.

Frequently Asked Questions

For most people, vitamin D3 is considered more effective. Research shows it is more potent at raising and maintaining serum vitamin D levels in the blood compared to D2, particularly with intermittent intake.

Yes, you can. Since vitamin D3 is generally more potent, achieving the same or a better result may require a different intake amount. Consult with a healthcare provider to determine the appropriate form and amount for your needs.

Yes, vitamin D2 is a viable option for vegans and vegetarians as it is plant-derived. While less potent than D3, it can contribute to vitamin D status with appropriate monitoring and potentially a different intake amount, as advised by a healthcare professional.

While both are absorbed effectively, the difference lies in metabolism and binding protein affinity. The metabolite of D2 is cleared from the bloodstream more rapidly than D3's, resulting in a less sustained effect on serum levels.

Food sources naturally contain either D2 (like UV-exposed mushrooms) or D3 (like fatty fish and eggs). The same potency differences apply, but dietary intake is typically lower than therapeutic amounts from supplements, so the effect is more gradual.

Some studies suggest that the potency difference between D2 and D3 may be less pronounced in individuals with a higher body mass index (BMI). This is because excess body fat can potentially affect the advantage of D3 over D2 in these individuals.

The best approach is to consult a healthcare provider, especially for higher intake amounts or to address a deficiency. Based on clinical studies, achieving a similar effect as D3 may require a higher intake of D2.