Is vitamin D3 really better than D2?

Yes, for daily supplementation. A Cochrane-reviewed meta-analysis found that D3 raises serum 25(OH)D levels approximately 87% more than D2 at equivalent doses. D3 also has a longer half-life in circulation. The only practical reason to choose D2 is if you require a strictly vegan source — though lichen-derived D3 is now widely available.

Should I take vitamin K2 with D3?

Many practitioners recommend combining D3 with K2 (as MK-7) because vitamin D3 increases calcium absorption, and K2 helps direct that calcium into bone rather than arterial walls. The evidence for the combination is supportive, particularly for individuals taking higher D3 doses. MK-7 has a longer half-life than MK-4, making once-daily dosing practical.

What is a standard vitamin D3 dose?

Common supplemental doses range from 1,000 to 5,000 IU daily for adults. The appropriate dose depends on baseline serum 25(OH)D levels, sun exposure, body weight, and individual factors. Serum testing before and after supplementation is the most reliable way to determine an effective personal dose. The tolerable upper intake level established by the Institute of Medicine is 4,000 IU/day, though many clinicians use higher doses under supervision.

Moderate Evidence

Best Form of Vitamin D: A Clinical Guide

Vitamin D is not a single molecule — two distinct forms are sold as supplements, and their clinical performance differs substantially. D3 (cholecalciferol) is the mammalian form, produced in skin under UV light. D2 (ergocalciferol) is derived from plant sources. Head-to-head trials consistently favor D3 for raising and maintaining serum 25(OH)D.

Updated 2026 · Reviewed by Dr. Brennan Commerford, D.C.

Our Recommendation

Our Pick

Vitamin D3 (Cholecalciferol)

Meta-analysis data show D3 raises serum 25(OH)D levels approximately 87% more effectively than an equivalent D2 dose. D3 is the form produced naturally by the skin in response to sunlight and is the standard of care in clinical practice.

All Forms Compared

Best

Vitamin D3 (Cholecalciferol)

Bioavailability

~87% more potent than D2

Best For

Immune support, bone health, general repletion

The mammalian form — identical to what skin synthesizes under UV light.

Best

Vitamin D3 + K2 (MK-7) Combination

Bioavailability

Same D3 potency, adds K2 routing

Best For

Bone mineral density support, cardiovascular health

MK-7 form of K2 helps direct calcium absorbed under D3 to bone matrix rather than soft tissue.

Avoid

Vitamin D2 (Ergocalciferol)

Bioavailability

~54% relative to D3

Best For

Vegan supplementation (plant-derived source)

Inferior at raising serum 25(OH)D with daily dosing. Vegan D3 from lichen is now widely available and is the preferred option.

Frequently Asked Questions

Is vitamin D3 really better than D2?: Yes, for daily supplementation. A Cochrane-reviewed meta-analysis found that D3 raises serum 25(OH)D levels approximately 87% more than D2 at equivalent doses. D3 also has a longer half-life in circulation. The only practical reason to choose D2 is if you require a strictly vegan source — though lichen-derived D3 is now widely available.
Should I take vitamin K2 with D3?: Many practitioners recommend combining D3 with K2 (as MK-7) because vitamin D3 increases calcium absorption, and K2 helps direct that calcium into bone rather than arterial walls. The evidence for the combination is supportive, particularly for individuals taking higher D3 doses. MK-7 has a longer half-life than MK-4, making once-daily dosing practical.
What is a standard vitamin D3 dose?: Common supplemental doses range from 1,000 to 5,000 IU daily for adults. The appropriate dose depends on baseline serum 25(OH)D levels, sun exposure, body weight, and individual factors. Serum testing before and after supplementation is the most reliable way to determine an effective personal dose. The tolerable upper intake level established by the Institute of Medicine is 4,000 IU/day, though many clinicians use higher doses under supervision.

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FormulaForge formulates and sells supplements containing the ingredients discussed on this page. Our formulary recommendations are based on peer-reviewed bioavailability research. All cited studies are independently verifiable.

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.