Vitamin A IU to mcg RAE Converter
Vitamin A IU to mcg RAE Converter
Convert vitamin A from international units to micrograms of retinol activity equivalent, using the correct factor for retinol, supplemental beta-carotene or dietary carotenoids.
Vitamin A IU to mcg RAE converter
IU → mcg RAE5,000 IU of preformed retinol
Formula and conversion factors
Retinol 0.3 · supplemental beta-carotene 0.3 · dietary beta-carotene 0.05 · dietary alpha-carotene or beta-cryptoxanthin 0.025
- RAE
- retinol activity equivalent — the current standard unit, which scales every provitamin A carotenoid to the retinol it actually delivers
- 0.3 vs 0.05
- supplemental beta-carotene is purified and oil-dispersed, so it is absorbed far more efficiently than the same carotenoid bound in a food matrix
- IU
- a legacy activity unit; it does not state which form of vitamin A it refers to, so the ingredient list must be checked before converting
Worked example
5,000 IU of preformed retinol
Retinol factor = 0.3 mcg RAE per IU
5,000 × 0.3 = 1,500.0 mcg RAE
Above the adult RDA of 900 mcg RAE, below the 3,000 mcg/day upper limit
Conversion factors by form
| Form | mcg RAE per IU | 1,000 IU | 5,000 IU | 10,000 IU |
|---|---|---|---|---|
| Retinol (preformed) | 0.3 | 300 | 1,500 | 3,000 |
| Supplemental beta-carotene | 0.3 | 300 | 1,500 | 3,000 |
| Dietary beta-carotene | 0.05 | 50 | 250 | 500 |
| Dietary alpha-carotene or beta-cryptoxanthin | 0.025 | 25 | 125 | 250 |
Adult reference values (mcg RAE per day)
| mcg RAE/day | Equivalent IU of retinol | |
|---|---|---|
| RDA, women | 700 | 2,333 |
| RDA, men | 900 | 3,000 |
| Tolerable upper intake level (preformed vitamin A) | 3,000 | 10,000 |
| Upper limit for provitamin A carotenoids | None set | — |
Why the IU factor depends on which form you took
An international unit of vitamin A is a unit of biological activity rather than a fixed mass, and how much retinol activity equivalent it represents depends entirely on the form supplied. Preformed retinol and supplemental beta-carotene both convert at 0.3 mcg RAE per IU. Dietary beta-carotene converts at 0.05, and dietary alpha-carotene or beta-cryptoxanthin at 0.025, so the same IU figure printed on two different products can differ twelvefold once it is expressed in RAE.
The gap between the supplemental and dietary carotenoid factors is a matter of absorption rather than chemistry. Carotenoids held within the plant matrix of a food are released and taken up far less efficiently than the purified, oil-dispersed beta-carotene in a capsule, and the intestinal cleavage of beta-carotene to retinal is itself saturable, becoming proportionally less efficient as intake rises. The RAE scale was introduced in 2001 for exactly this reason: the older retinol equivalent figures overstated how much vitamin A dietary carotenoids actually deliver.
The tolerable upper intake level of 3,000 mcg/day applies to preformed vitamin A only. No upper limit has been set for provitamin A carotenoids, because conversion is downregulated once hepatic stores are adequate. A large, sustained carotenoid intake therefore produces carotenodermia — a harmless orange-yellow discolouration of the palms, soles and nasolabial folds that characteristically spares the sclerae — rather than hypervitaminosis A. A converted figure cannot be read against the upper limit without knowing which form it came from, which is why the warning about excess intake on this page appears only when the form selected is preformed retinol.
Preformed vitamin A is teratogenic, and the upper limit matters most in pregnancy, where high retinol intake from supplements, liver or systemic retinoids is associated with craniofacial and central nervous system malformations. Chronic excess in anyone else causes headache, dry skin, alopecia, hyperostosis and hepatotoxicity. IU labelling is a legacy convention that has been superseded by mcg RAE, and a product still declaring IU will often not say which form the figure refers to — read the ingredient list before converting, because guessing the factor is the main way this calculation goes wrong.
Frequently asked questions
How many mcg RAE are in 5,000 IU of vitamin A?
1,500 mcg RAE if the source is preformed retinol or supplemental beta-carotene, using a factor of 0.3. The same 5,000 IU from dietary beta-carotene is only 250 mcg RAE, because the dietary factor is 0.05.
Why do dietary and supplemental beta-carotene use different factors?
Absorption differs. Beta-carotene bound in a plant food matrix is released and absorbed far less efficiently than purified beta-carotene dispersed in oil in a supplement, and the conversion of beta-carotene to retinal becomes less efficient as intake rises.
Does the 3,000 mcg upper limit apply to beta-carotene?
No. The tolerable upper intake level of 3,000 mcg/day applies to preformed vitamin A only. No upper limit has been set for provitamin A carotenoids, since conversion is downregulated when stores are adequate.
Is a high beta-carotene intake harmful?
It causes carotenodermia — an orange-yellow discolouration of the palms, soles and nasolabial folds that spares the sclerae and resolves when intake falls — rather than vitamin A toxicity. High-dose beta-carotene supplements have separately been associated with increased lung cancer risk in smokers.
Why does vitamin A matter more in pregnancy?
Preformed vitamin A is teratogenic. High retinol intake in pregnancy, from supplements, liver or systemic retinoids, is associated with craniofacial and central nervous system malformations, so the upper limit is the number that matters most in this group.
Related calculators
References
- National Institutes of Health, Office of Dietary Supplements. Vitamin A and Carotenoids: Fact Sheet for Health Professionals. Bethesda, MD: NIH ODS.
- Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. National Academies Press; 2001.