Vitamin D2 vs D3: What’s the Difference and Which Is Better?

Understanding the Two Forms of Vitamin D

Vitamin D is a fat-soluble nutrient that exists in several forms. The two most common in supplements and fortified foods are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). While both can help you maintain adequate vitamin D status, they are not identical. Vitamin D2 and D3 differ primarily in their chemical structure, how they are produced, and their natural dietary sources. These differences can influence how each form behaves in the body, especially when it comes to raising and maintaining blood levels of 25-hydroxyvitamin D [25(OH)D], the form doctors typically measure to assess vitamin D status.

Sources: National Institutes of Health Office of Dietary Supplements (NIH ODS)

How Vitamin D2 and D3 Are Made

Vitamin D2 is manufactured by irradiating ergosterol, a compound found in yeast, with ultraviolet (UV) light. Vitamin D3, on the other hand, is typically produced by irradiating 7-dehydrocholesterol, a substance derived from lanolin, which is the oil extracted from sheep's wool. An animal-free version of vitamin D3, sourced from lichen, is also available for those who prefer a vegan option.

Sources: National Institutes of Health Office of Dietary Supplements (NIH ODS)

Dietary Sources of Vitamin D2 vs D3

In nature, vitamin D2 is found in certain mushrooms and yeast that have been exposed to ultraviolet light. Foods like UV-treated portobello mushrooms can provide vitamin D2. Vitamin D3, however, is found in animal-based foods such as fatty fish (salmon, mackerel, tuna), fish liver oils, egg yolks, and beef liver. Moreover, vitamin D3 is the form your skin produces when exposed to sunlight's ultraviolet B (UVB) rays.

• Food sources of vitamin D2: UV-exposed mushrooms, other UV-exposed fungi.
• Food sources of vitamin D3: fatty fish, fish liver oil, egg yolks, beef liver.

Sources: National Institutes of Health Office of Dietary Supplements (NIH ODS)

Absorption and Metabolism: How Each Form Works in the Body

Both vitamin D2 and D3 are well absorbed in the small intestine. After absorption, they are transported to the liver, where they undergo hydroxylation. Vitamin D2 is converted to 25-hydroxyvitamin D2, while vitamin D3 becomes 25-hydroxyvitamin D3. These forms are then further processed in the kidneys to the active hormone, calcitriol. Despite sharing these steps, subtle differences in their metabolism and binding can lead to different effects on blood levels.

Sources: National Institutes of Health Office of Dietary Supplements (NIH ODS)

Effectiveness in Raising and Maintaining Blood Levels

Multiple studies and meta-analyses have compared the efficacy of D2 and D3. A 2021 systematic review and meta-analysis of 24 studies concluded that vitamin D3 was more effective than vitamin D2 in raising total 25(OH)D levels, with a mean difference of 15.69 nmol/L. The same review also found that vitamin D3 was more effective in reducing parathyroid hormone (PTH) levels, a marker of vitamin D adequacy. However, not all studies show a clear advantage. A 2013 study in healthy adults found that taking 1000 IU of either D2 or D3 daily for 11 weeks produced similar increases in total 25(OH)D. Additionally, a 2022 retrospective study using injectable forms found that a D3 injection raised serum vitamin D by a mean of 6.1 ng/ml compared to 3.2 ng/ml for a D2 injection, even when the D2 dose was twice the amount (600,000 U vs 300,000 U). This suggests that D3 may be more potent when given in large doses. The National Institutes of Health (NIH) notes that most evidence indicates vitamin D3 raises serum 25(OH)D to a greater extent and maintains those higher levels longer than vitamin D2.

Sources: Nutrients (MDPI), The Journal of Clinical Endocrinology & Metabolism (Endocrine Society), National Institutes of Health Office of Dietary Supplements (NIH ODS), Qatar Medical Journal

Considerations for Vegans and Vegetarians

Since conventional vitamin D3 is derived from lanolin (sheep's wool), many vegans and vegetarians prefer vitamin D2, which is always animal-free. However, lichen-derived vitamin D3 offers a vegan-friendly alternative. Lichen is a composite organism that is not an animal, and it can produce vitamin D3. Thus, you can find vitamin D3 supplements that are suitable for vegan diets. If you follow a plant-based diet, you may have a higher risk of low vitamin D levels because the best natural sources (fatty fish, egg yolks) are animal-based. Be sure to check supplement labels for the source of vitamin D3.

Sources: National Institutes of Health Office of Dietary Supplements (NIH ODS), Cleveland Clinic

recommendations on form preference

Professional organizations and health experts generally recommend vitamin D3 over D2 for supplementation. For instance, Cleveland Clinic physicians state that vitamin D3 is generally more effective and longer-acting than D2. An endocrinologist at Columbia University Irving Medical Center notes that most doctors recommend D3 because it is slightly more active and effective. However, this does not mean D2 is ineffective. In the United States, vitamin D2 is the form traditionally available as a high-dose prescription (e.g., 50,000 IU capsules), while D3 is more common in over-the-counter supplements. If a healthcare provider prescribes high-dose vitamin D, they may choose D2 due to insurance or availability, but this does not imply D3 is inferior.

Sources: Cleveland Clinic, Qatar Medical Journal, Columbia University Irving Medical Center

Side-by-Side Comparison: D2 vs D3

The table below summarizes the key similarities and differences between vitamin D2 and D3 based on the evidence from this guide.

Sources: National Institutes of Health Office of Dietary Supplements (NIH ODS), Nutrients (MDPI), Cleveland Clinic, The Journal of Clinical Endocrinology & Metabolism (Endocrine Society)

How to Choose Between D2 and D3

For most people, vitamin D3 appears to be the more effective choice based on current evidence. It tends to raise blood levels of 25(OH)D higher and sustain them longer. If you follow a vegan or vegetarian diet, look for lichen-derived vitamin D3 to align with your preferences while still getting the potentially more beneficial form. Vitamin D2 is still an adequate form, especially when used at the high prescription doses. The choice also depends on availability and cost. Over-the-counter vitamin D2 is less common but exists; check labels. Always consult your healthcare provider before starting a supplement, especially at high doses, to avoid overdose and ensure you address any underlying deficiency.

Sources: National Institutes of Health Office of Dietary Supplements (NIH ODS), Nutrients (MDPI), Cleveland Clinic