Vitamin D, a vital fat-soluble nutrient, supports bone health, immune function, and overall well-being. Sunlight is a primary source, but diet and supplements are often necessary, especially in areas with limited sun. Two main forms exist: D2 and D3, which differ in origin, metabolism, and efficacy in raising blood vitamin D levels.
The Different Forms of Vitamin D
Human nutrition involves two main forms:
- Vitamin D2 (Ergocalciferol): This plant-derived form comes from UV-irradiated yeast and fungi and is used in fortified foods like cereals and plant milks. Prescription D2 can treat deficiencies.
- Vitamin D3 (Cholecalciferol): This form is made in human skin from sun exposure and found in animal products like fatty fish and eggs. Vegan D3 from lichen is also available. Most supplements contain D3 due to its effectiveness.
How the Body Processes Vitamin D
The body converts both D2 and D3 through two steps:
- Liver: Conversion to 25-hydroxyvitamin D (calcidiol), the main circulating form measured in blood tests.
- Kidneys: Further conversion to the active form, 1,25-dihydroxyvitamin D (calcitriol).
Vitamin D2 vs. Vitamin D3: The Effectiveness Debate
While both forms can address deficiency, evidence strongly suggests D3 is superior for raising and maintaining vitamin D levels.
Superior Efficacy of Vitamin D3
Research consistently shows that D3 is more potent and lasts longer in the body than D2. Meta-analyses confirm D3 leads to greater increases in blood 25(OH)D and more effectively lowers parathyroid hormone levels. This difference may be due to how they bind to transport proteins and their clearance rates.
Conflicting Evidence
Some studies, particularly with lower doses, have shown D2 and D3 to be equally effective. However, the advantage of D3 is more apparent with higher doses or less frequent intake, and when treating significant deficiencies.
Sources and Supplementation Options
Adequate vitamin D comes from sun, diet, and supplements. A combination is often needed.
Food Sources of Vitamin D
- D3-rich foods: Fatty fish, fish liver oils, egg yolks, beef liver.
- D2-rich foods: UV-exposed mushrooms, fortified foods like milk and cereal.
Choosing a Vitamin D Supplement
Most health professionals recommend D3 for supplementation due to its better efficacy.
- Over-the-counter D3 is suitable for maintenance.
- Vegan D3 from lichen is an option for plant-based diets.
- Prescription high-dose supplements, either D2 or D3, may be used for severe deficiencies.
- Vitamin D absorption is enhanced when taken with a meal containing fat.
Comparison of Vitamin D2 and D3
| Feature | Vitamin D2 (Ergocalciferol) | Vitamin D3 (Cholecalciferol) |
|---|---|---|
| Primary Source | Plant-based (fungi), fortified foods | Animal-based (fatty fish, skin from sun), vegan lichen sources |
| Efficacy | Less effective at raising and sustaining blood levels | More effective at raising and sustaining blood levels |
| Potency | Considered less potent per equivalent dose in many studies | More potent, especially at higher doses |
| Stability | More susceptible to degradation over time | More stable during storage and processing |
| Bioavailability | Good initial absorption, but differences in metabolism lead to reduced effectiveness | Better utilized by the body after absorption |
| Use | Commonly used in fortified foods and higher-dose prescriptions | Widely available in over-the-counter supplements and fortified products |
Conclusion: Choosing the Right Form for You
For most individuals supplementing for health, vitamin D3 is the more effective choice due to its superior ability to raise and maintain vitamin D levels. Vegan D3 from lichen is available for those on plant-based diets. Consulting a healthcare provider is recommended to determine your vitamin D status and get personalized advice on the best form and dosage. Taking vitamin D with fat aids absorption.
To learn more about nutrient recommendations, consult the National Institutes of Health Office of Dietary Supplements.
