Vitamin D · unit conversion
Pick the chemical form the label names, then the direction. Nothing is converted until a form is chosen, because the same number of IU is a different mass for each form.
Result
Choose a form first. IU is not a mass, so without the form there is no factor that can be said to apply.
The factors on this page
| Form | From | To | Factor | Source | Year |
|---|---|---|---|---|---|
| Cholecalciferol, D3 (vitamin D) | IU | mcg | 0.025 | FDA Guidance for Industry: Converting Units of Measure for Folate, Niacin, and Vitamins A, D, and E on the Nutrition and Supplement Facts Labels | 2019 |
| Cholecalciferol, D3 (vitamin D) | mcg | IU | 40 | FDA Guidance for Industry: Converting Units of Measure for Folate, Niacin, and Vitamins A, D, and E on the Nutrition and Supplement Facts Labels | 2019 |
| Ergocalciferol, D2 (vitamin D) | IU | mcg | 0.025 | FDA Guidance for Industry: Converting Units of Measure for Folate, Niacin, and Vitamins A, D, and E on the Nutrition and Supplement Facts Labels | 2019 |
| Ergocalciferol, D2 (vitamin D) | mcg | IU | 40 | FDA Guidance for Industry: Converting Units of Measure for Folate, Niacin, and Vitamins A, D, and E on the Nutrition and Supplement Facts Labels | 2019 |
As published
One IU of vitamin D has been previously defined as the activity of 0.025 mcg of cholecalciferol (Vitamin D3) in bioassays with rats and chicks (Ref. 9): 1 mcg cholecalciferol = 40 IU vitamin D. [Treated as an exact, fixed potency definition, not a rounded approximation; this is the factor FDA applies under 21 CFR 101.9(c)(8)(iv) for the optional parenthetical IU declaration alongside the mandatory mcg value.]
FDA Guidance for Industry: Converting Units of Measure for Folate, Niacin, and Vitamins A, D, and E on the Nutrition and Supplement Facts Labels
One IU of vitamin D has been previously defined as the activity of 0.025 mcg of cholecalciferol (Vitamin D3) in bioassays with rats and chicks (Ref. 9): 1 mcg cholecalciferol = 40 IU vitamin D.
FDA Guidance for Industry: Converting Units of Measure for Folate, Niacin, and Vitamins A, D, and E on the Nutrition and Supplement Facts Labels
Table 4. Conversion factor from IU to mcg of vitamin D ... Vitamin D2 (ergocalciferol) / Vitamin D3 (cholecalciferol) ... 0.025. The two major forms of vitamin D, vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol), have been reported to exhibit identical responses in the body (Ref. 9), so for the purpose of converting from IU to mcg, we consider them to be bioequivalent. [This is a stated labelling convention — an assumed bioequivalence to D3 — not an independently assayed exact constant for D2 itself.]
FDA Guidance for Industry: Converting Units of Measure for Folate, Niacin, and Vitamins A, D, and E on the Nutrition and Supplement Facts Labels
The two major forms of vitamin D, vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol), have been reported to exhibit identical responses in the body (Ref. 9), so for the purpose of converting from IU to mcg, we consider them to be bioequivalent. [Read with the D3 sentence "1 mcg cholecalciferol = 40 IU vitamin D": a stated labelling convention, not an assayed constant for D2 itself.]
FDA Guidance for Industry: Converting Units of Measure for Folate, Niacin, and Vitamins A, D, and E on the Nutrition and Supplement Facts Labels