Vitamin D2 (Ergocalciferol)
Also known as: Ergocalciferol, Calciferol, Viosterol
Ergocalciferol (Vitamin D2) is a secosteroid that plays a crucial role in calcium homeostasis, bone metabolism, and immune function. While both D2 and D3 forms effectively raise serum 25-hydroxyvitamin D levels, research indicates that D3 may be more potent and maintain levels for a longer duration. However, D2 is widely used in supplements and fortified foods, particularly for vegetarians and vegans, and is effective in treating vitamin D deficiency. Its primary mechanism involves binding to the vitamin D receptor (VDR) after metabolic activation, influencing gene expression related to calcium absorption and immune response.
Last reviewed: 2026-04-22 · 4 indexed studies
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Overview
Vitamin D2, or ergocalciferol, is one of the two major forms of vitamin D, the other being vitamin D3 (cholecalciferol). It is produced in plants and fungi upon exposure to ultraviolet (UV) B radiation. Ergocalciferol can be obtained through the diet from fortified foods or supplements. Like vitamin D3, vitamin D2 must undergo hydroxylation in the liver and kidneys to become its biologically active form, calcitriol (1,25-dihydroxyvitamin D).
Mechanism & Function
Ergocalciferol (D2) · C₂₈H₄₄O — source: PubChem CID 5280793
Pale yellow plant-derived vitamin D oil. Less potent per IU than D3.
- Softgel
- Capsule
- Liquid
- Tablet
Softgel is generally preferred for bioavailability or efficacy.
Mechanism of Action
Ergocalciferol is metabolised in the liver to 25-hydroxyvitamin D2 (25(OH)D2) and subsequently in the kidneys to 1,25-dihydroxyvitamin D2 (1,25(OH)2D2), which is the active form. This active form binds to the vitamin D receptor (VDR) in target cells, leading to altered gene transcription that regulates calcium and phosphate metabolism, cell proliferation, differentiation, and immune function.
Physiological Role
Vitamin D2 contributes to maintaining serum calcium and phosphate concentrations within a normal range by promoting their absorption in the gut, reabsorption in the kidneys, and mobilisation from bone. It is critical for bone mineralisation, regulation of parathyroid hormone secretion, and modulating innate and adaptive immune responses. It also influences cell growth and differentiation.
Primary Pathways
Performance / Health Relevance
While not directly enhancing athletic performance, adequate vitamin D (including D2) is crucial for athletes due to its role in bone health, muscle function, and immune system support. Deficiency can lead to increased risk of stress fractures, muscle weakness, and impaired immune function, potentially impacting training and recovery.
Evidence Review
Compare Vitamin D Forms
Full comparison2 vitamin d forms are indexed. Bioavailability, clinical evidence, and best-use cases differ meaningfully between them.
| Form | Evidence |
|---|---|
Vitamin D2 (Ergocalciferol)This page Fat-soluble vitamin; absorption is enhanced when consumed with dietary fat. Requires hydroxylation in liver and kidney for activation. | 65/100 |
| Vitamin D3 D3 is 87% more potent than D2 at raising serum 25(OH)D. Oil-based delivery enhances absorption. | 91/100 |
Practical Use & Dosage
- Minimum Effective Dose
- 600 IU (15 mcg) daily for general health; higher doses for deficiency treatment.
- Optimal Range
- 600-2,000 IU (15-50 mcg) daily for maintenance; 10,000-50,000 IU daily or weekly for acute deficiency, under medical supervision.
- Upper / Caution Level
- 4,000 IU (100 mcg) daily for adults is the UL for total vitamin D intake. Doses up to 10,000 IU/day have been used safely under medical guidance for deficiency.
- Timing
- Can be taken at any time of day, preferably with a meal containing fat to enhance absorption.
- Best Format
- Tablets, capsules, or liquid drops. Should be formulated for stability against light and oxygen.
- Bioavailability
- Fat-soluble vitamin; absorption is enhanced when consumed with dietary fat. Requires hydroxylation in liver and kidney for activation.
- Absorption Considerations
- Absorption can be impaired in individuals with malabsorption syndromes (e.g., Crohn's disease, cystic fibrosis, celiac disease), obesity, or after gastric bypass surgery. Bioavailability may be slightly lower than vitamin D3.
Safety & Interactions
Side Effects
- •Hypercalcaemia (at very high doses)
- •Nausea
- •Vomiting
- •Weakness
- •Polyuria
- •Constipation
- •Kidney stones (rare, at very high doses long-term)
Contraindications
- Hypercalcaemia
- Hypervitaminosis D
- Severe renal impairment (use with caution and monitor)
- Sarcoidosis (use with caution due to increased sensitivity)
Drug Interactions
- •Corticosteroids (may reduce vitamin D effects)
- •Orlistat (may reduce vitamin D absorption)
- •Cholestyramine and colestipol (may reduce vitamin D absorption)
- •Phenytoin and barbiturates (may increase vitamin D metabolism)
- •Thiazide diuretics (may increase risk of hypercalcaemia)
- •Digoxin (hypercalcaemia may exacerbate digoxin toxicity)
Who Should Avoid
- •Individuals with pre-existing hypercalcaemia or hypervitaminosis D. Those with certain medical conditions should consult a doctor.
Monitoring
Serum 25-hydroxyvitamin D levels should be monitored, especially when initiating high-dose therapy or in individuals with conditions affecting vitamin D metabolism. Serum calcium and phosphate levels should also be monitored.
Frequently Asked Questions
Auto-generated from indexed evidence — dosage, safety, interactions, and more.
When is Vitamin D2 (Ergocalciferol) typically used or indicated?
Vitamin D2 (Ergocalciferol) is most commonly used for: Bone Health Support, Vitamin D Deficiency, Immune Support, Adjunct in Psoriasis Treatment. Vitamin D2 contributes to maintaining serum calcium and phosphate concentrations within a normal range by promoting their absorption in the gut, reabsorption in the kidneys, and mobilisation from bone. It is critical for bone mineralisation, regulation of parathyroid hormone secretion, and modulating innate and adaptive immune responses. It also influences cell growth and differentiation.
How does Vitamin D2 (Ergocalciferol) work?
Ergocalciferol is metabolised in the liver to 25-hydroxyvitamin D2 (25(OH)D2) and subsequently in the kidneys to 1,25-dihydroxyvitamin D2 (1,25(OH)2D2), which is the active form. This active form binds to the vitamin D receptor (VDR) in target cells, leading to altered gene transcription that regulates calcium and phosphate metabolism, cell proliferation, differentiation, and immune function.
What is the recommended dose of Vitamin D2 (Ergocalciferol)?
The optimal range is 600-2,000 IU (15-50 mcg) daily for maintenance; 10,000-50,000 IU daily or weekly for acute deficiency, under medical supervision.. with a minimum effective dose of 600 IU (15 mcg) daily for general health; higher doses for deficiency treatment.. Best taken: Can be taken at any time of day, preferably with a meal containing fat to enhance absorption.. Upper / caution level: 4,000 IU (100 mcg) daily for adults is the UL for total vitamin D intake. Doses up to 10,000 IU/day have been used safely under medical guidance for deficiency..
What are the side effects of Vitamin D2 (Ergocalciferol)?
Reported side effects include: Hypercalcaemia (at very high doses); Nausea; Vomiting; Weakness; Polyuria; Constipation; and Kidney stones (rare, at very high doses long-term). Monitoring: Serum 25-hydroxyvitamin D levels should be monitored, especially when initiating high-dose therapy or in individuals with conditions affecting vitamin D metabolism. Serum calcium and phosphate levels should also be monitored.
Does Vitamin D2 (Ergocalciferol) interact with medications?
Known or theoretical interactions: Corticosteroids (may reduce vitamin D effects); Orlistat (may reduce vitamin D absorption); Cholestyramine and colestipol (may reduce vitamin D absorption); Phenytoin and barbiturates (may increase vitamin D metabolism); Thiazide diuretics (may increase risk of hypercalcaemia); and Digoxin (hypercalcaemia may exacerbate digoxin toxicity). Always check with a clinician before combining with prescription medication.
Who should avoid Vitamin D2 (Ergocalciferol)?
Vitamin D2 (Ergocalciferol) is generally not recommended for: Individuals with pre-existing hypercalcaemia or hypervitaminosis D. Those with certain medical conditions should consult a doctor.; Hypercalcaemia; Hypervitaminosis D; Severe renal impairment (use with caution and monitor); and Sarcoidosis (use with caution due to increased sensitivity).
How strong is the evidence for Vitamin D2 (Ergocalciferol)?
Evidence level: Moderate (overall score 65/100), based on 4 indexed studies on SuppIndex.
Research & References (4)
A comparative study of vitamin D2 and vitamin D3 supplementation in the maintenance of 25-hydroxyvitamin D levels in healthy individuals.
This randomised controlled trial compared the efficacy of vitamin D2 versus vitamin D3 in maintaining serum 25-hydroxyvitamin D levels over 12 weeks. Participants received either 1000 IU of vitamin D2 or vitamin D3 daily.
Vitamin D2 is much less effective than vitamin D3 in humans.
This study critically reviewed the efficacy of vitamin D2 compared to vitamin D3 in humans, drawing on both clinical and mechanistic data, suggesting that D2 may be less potent.
Comparison of vitamin D2 and vitamin D3 supplementation for the treatment of vitamin D deficiency: a systematic review and meta-analysis.
This systematic review and meta-analysis aimed to compare the effectiveness of vitamin D2 and D3 in treating vitamin D deficiency by pooling data from multiple clinical trials.
Effect of vitamin D2 administration on serum 25(OH)D concentrations in children with vitamin D deficiency.
This randomised controlled trial investigated the efficacy of oral vitamin D2 supplementation in deficient children.
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Research Overview
Moderate EvidenceCite this ingredient
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Stable URL
https://thesuppindex.com/ingredients/vitamin-d2-ergocalciferol
SuppIndex. (2026). Vitamin D2 (Ergocalciferol): Evidence summary, dosage and clinical studies. Retrieved October 25, 2026, from https://thesuppindex.com/ingredients/vitamin-d2-ergocalciferol
Based on 4 indexed studies · Evidence level: Moderate.
Goal Ratings
Stack Compatibility
Generally safe to stack with most supplements. May be beneficial to stack with calcium and magnesium for bone health, but monitor total calcium intake.