Glossary · Vitamin D
Abbreviations on vitamin D packaging
Vitamin D has the simplest maths of all supplements and can still be confusing. It all comes down to two units that describe exactly the same thing.
On one package you will see “2000 IU”, on another “50 µg”, and on a third both numbers together. It is the same amount of vitamin, expressed differently. The conversion is fixed and does not depend on the manufacturer or the form: 1 µg equals 40 IU.
The remaining differences come down to the vitamin form and what the manufacturer has added alongside it. Only that makes two products described as “2000 IU” incomparable.
The terms one by one
- IUinternational unit
- A way of expressing the amount of fat-soluble vitamins. The conversion is fixed: 1 µg equals 40 IU, so 25 µg equals 1000 IU, and 50 µg equals 2000 IU. You will more often see IU on the front of the package because the number is simply larger and looks better.
- µgmicrogram
- A unit of mass used in the nutrition table because regulations require it. When the front says “4000 IU”, the table shows “100 µg” — these are not two different doses, but one amount written twice.
- Cholecalciferolvitamin D3
- The form found in most supplements. It is obtained from lanolin, a fat from sheep's wool, or from lichen — the latter version may be labelled as suitable for vegans, and that is the only difference visible directly from the label.
- Ergocalciferolvitamin D2
- A form of fungal origin, encountered less often. We do not place it in one table with D3 without clearly marking the difference, because it is not a one-to-one substitute.
- MK-7menaquinone-7
- A form of vitamin K2 often added to products with vitamin D. Its presence changes the product enough that we compare it separately from pure D3 — otherwise the price difference would appear to be a difference in value.
- Oil carrieroil in a capsule
- Vitamin D dissolves in fat, so the capsule contains oil: MCT, olive, flaxseed or fish oil. This is descriptive information, but it can matter for allergies and plant-based diets.
Other groups of terms
Omega-3 Magnesium, zinc, iron Vitamin C B vitamins Collagen Creatine Probiotics Label and calculations
How the numbers from a label turn into the cost of a day is shown in the omega-3 calculator — for now this is the only finished category. The rules by which we build the ranking are described in the How we rank section.