Vitamin D is one of the most widely recommended supplements in the world — and for good reason. Research links adequate vitamin D levels to immune function, bone density, mood regulation, cardiovascular health, and much more. Yet despite its importance, vitamin D deficiency remains one of the most common nutritional deficiencies globally.
If you've shopped for a vitamin D supplement, you've likely noticed two forms on labels: Vitamin D3 (cholecalciferol) and Vitamin D2 (ergocalciferol). While both raise blood levels of vitamin D, they are not equal in effectiveness. Here's what the science says.
What is Vitamin D3?
Vitamin D3 (cholecalciferol) is the form of vitamin D produced naturally in human skin upon exposure to UVB sunlight. It is also found in animal-based foods such as fatty fish, egg yolks, and liver. D3 is the form used in the vast majority of high-quality dietary supplements.
When D3 enters the body, it is converted in the liver to 25-hydroxyvitamin D (25(OH)D) — the storage form measured in blood tests — and then further activated in the kidneys to 1,25-dihydroxyvitamin D (calcitriol), the biologically active hormone.
What is Vitamin D2?
Vitamin D2 (ergocalciferol) is derived from plant sources, primarily UV-irradiated yeast and fungi. It has historically been used in prescription vitamin D supplements and food fortification. D2 is also the form used in most vegan vitamin D supplements.
D3 vs D2: What the Research Shows
Multiple clinical studies have compared the effectiveness of D3 and D2 at raising and maintaining blood levels of 25(OH)D:
- D3 is more potent: Studies consistently show that D3 raises serum 25(OH)D levels approximately 87% more effectively than D2 at equivalent doses
- D3 has a longer half-life: D3 maintains elevated blood levels for longer after supplementation stops, suggesting superior storage and utilization
- D3 is more stable: D3 is more stable during storage and has a longer shelf life than D2
- D2 may be adequate at high doses: At very high prescription doses, D2 can raise vitamin D levels, but D3 remains the preferred form for supplementation
The consensus among nutrition researchers and clinical practitioners is clear: Vitamin D3 is the preferred supplemental form for most people.
What About Vegan Vitamin D3?
Traditional D3 is derived from lanolin (sheep's wool), making it unsuitable for vegans. However, vegan D3 sourced from lichen (Cladonia rangiferina) is now widely available and provides the same cholecalciferol form as animal-derived D3 — making it the best choice for plant-based individuals.
How Much Vitamin D Do You Need?
The official RDA for vitamin D is 600–800 IU per day for most adults, but many researchers and clinicians argue this is insufficient to maintain optimal blood levels. Most functional medicine practitioners target serum 25(OH)D levels of 40–60 ng/mL, which often requires supplemental doses of 2,000–5,000 IU daily depending on baseline levels, sun exposure, body weight, and individual absorption.
Always test your vitamin D levels before and after supplementation to determine your optimal dose. A simple blood test (25-hydroxyvitamin D) is available through your healthcare provider.
D3 + K2: Why the Combination Matters
Vitamin D3 promotes calcium absorption from the gut — but without adequate Vitamin K2, that calcium may not be properly directed to bones and teeth. K2 (specifically MK-7) activates osteocalcin and matrix Gla protein, which help direct calcium to bones and away from soft tissues like arteries. For this reason, many practitioners recommend taking D3 and K2 together, especially at higher D3 doses.
Shop Vitamin D3 at Best Vitamins Online
Life Extension
- Life Extension Vitamin D3 5,000 IU 60 Softgels — a research-backed potency for immune and bone health
- Life Extension Vitamin D3 7,000 IU 60 Softgels — higher potency for those with greater deficiency needs
Pure Encapsulations
- Pure Encapsulations Vitamin D3 5,000 IU 120 Capsules — hypoallergenic, third-party tested D3 in a generous 120-count
- Pure Encapsulations Vitamin D3 & K2 4,000 IU / 100 mcg 120 Capsules — the synergistic D3 + K2 combination for bone and cardiovascular health
- Pure Encapsulations Vitamin D3 Vegan 120 Capsules — lichen-sourced D3 for vegan supplementation
Metagenics
- Metagenics Vitamin D3 5,000 IU 60 Softgels — professional-grade D3 from a practitioner-trusted brand
- Metagenics Vitamin D3 2,000 IU 90 Tablets — a moderate daily maintenance dose
- Metagenics MetaKids Vitamin D3 Liquid 2 fl oz — liquid D3 for children and those who prefer drops
NOW Foods
- NOW Foods Vitamin D3 5,000 IU 120 Chewable Tablets — a convenient chewable format for those who dislike swallowing capsules
- NOW Foods Vitamin D3 1,000 IU 180 Chewable Tablets — a lower-dose daily maintenance option
Douglas Laboratories
- Douglas Laboratories Vitamin D 5,000 IU 100 Tablets — clinical-grade D3 from a brand trusted by practitioners since 1955
- Douglas Laboratories Liquid Vitamin D-3 0.75 oz — liquid drops for precise, flexible dosing
The Bottom Line
Choose Vitamin D3 over D2 for superior absorption, potency, and duration of effect. Pair it with Vitamin K2 (MK-7) at higher doses for optimal calcium metabolism. Test your levels, work with your healthcare provider to find your optimal dose, and choose a third-party tested product from a brand you trust.
These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.