Vitamin D supplements: forms, units and labels
The two forms of vitamin D, how to convert between IU and micrograms, and what to check on the label.
Updated 15 November 2026 · Published by Radiant Life Distributors
D3 and D2
Vitamin D supplements contain one of two forms: vitamin D3 (cholecalciferol), the form in most supplements, or vitamin D2 (ergocalciferol). D3 is traditionally made from lanolin (sheep's wool), so people avoiding animal products should look for products labelled vegan, which use D3 from lichen or use D2.
IU and micrograms
Labels state vitamin D in micrograms (µg or mcg), international units (IU), or both.
1 microgram of vitamin D = 40 IU. So 25 µg = 1,000 IU, and 50 µg = 2,000 IU.
| Micrograms | International units |
|---|---|
| 10 µg | 400 IU |
| 25 µg | 1,000 IU |
| 50 µg | 2,000 IU |
| 125 µg | 5,000 IU |
Formats
Vitamin D comes as tablets, capsules, softgels, liquid drops and oral sprays, and in combination products with calcium, magnesium or vitamin K. For drops and sprays, check the dose per drop or per spray — not per bottle.
Choosing a dose
Strengths on the shelf range widely, and the right amount depends on your circumstances. Vitamin D is fat-soluble, so more is not automatically better. Ask your doctor or pharmacist what suits you — especially if you've had a blood test, take other medicines or are pregnant — and follow the label directions.
Where to buy
General information only, not medical advice. Supplements are not a substitute for a varied diet. Always read the label and follow the directions for use, and check with your pharmacist or doctor before starting a supplement, especially if you take other medicines, are pregnant or are managing a health condition.
Questions
How many IU is 25 micrograms of vitamin D?
1,000 IU. One microgram of vitamin D equals 40 IU.
What is the difference between vitamin D3 and D2?
D3 is cholecalciferol, the form in most supplements; D2 is ergocalciferol. Both appear on labels by name.
Is vitamin D3 vegan?
Usually not — D3 is traditionally made from lanolin. Look for products labelled vegan, which use D3 from lichen or use D2.
How much vitamin D should I take?
That depends on your circumstances. Ask your doctor or pharmacist and follow the label directions.