Vitamin D3 vs D2: Which One Should You Actually Buy?

Vitamin D is one of the most important nutrients for immune function, bone health, and mood regulation. But when you walk into a supplement store, you'll find two forms: D2 (ergocalciferol) and D3 (cholecalciferol). Which one should you actually buy?

The short answer: D3 is generally the better choice. But the full picture is more nuanced, and understanding the differences will help you make a smarter purchase.

The Key Differences

Factor	Vitamin D2	Vitamin D3
Source	Lichen / fungi	Sheep's wool (lanolin) or lichen-derived
Absorption	Modest	Superior
Bioavailability	Lower	Higher (studies show ~87% more effective)
Duration	Shorter-lasting	Longer-lasting in bloodstream
Vegan	Yes (naturally)	Only lichen-derived versions
Common Dosage	5,000–50,000 IU	1,000–5,000 IU

Why D3 Is Generally Preferred

Multiple studies have shown that D3 is more effective at raising and maintaining blood vitamin D levels than D2. A landmark study published in the American Journal of Clinical Nutrition found that D3 was significantly more effective at sustaining vitamin D status over a full year.

Here's why this matters: if you're deficient in vitamin D (which a large portion of the global population is), you want the form that gets your levels back up fastest and keeps them there longest.

When D2 Might Make Sense

D2 isn't useless. There are situations where it might be appropriate:

• Strict vegan/vegetarian: D2 is naturally plant-based, though vegan D3 from lichen is now widely available
• Prescription-strength doses: Doctors sometimes prescribe high-dose D2 (50,000 IU) for short-term correction
• Allergy considerations: Some people are sensitive to lanolin-derived D3

How Much Vitamin D Should You Take?

General recommendations vary by source, but most experts agree:

• Maintenance: 1,000–2,000 IU daily for most adults
• Deficiency correction: 5,000 IU daily (under medical supervision)
• Maximum safe dose: 4,000 IU/day without medical supervision

Get your levels tested if possible. A simple 25(OH)D blood test can tell you exactly where you stand.

Our Recommendations

Final Verdict

For most people, vitamin D3 is the clear winner. It's more bioavailable, lasts longer in your system, and is the form your body naturally produces from sunlight.

Choose D3 from a reputable brand with third-party testing, take it with a meal containing fat (it's fat-soluble), and consider getting your levels checked periodically.