Vitamin E IU to mg Converter
Vitamin E IU to mg Converter
Convert vitamin E from international units to milligrams of alpha-tocopherol, using the correct factor for the natural or the synthetic form.
Vitamin E IU to mg converter
IU → mg400 IU of natural RRR-alpha-tocopherol (d-alpha)
Formula and conversion factors
Natural RRR-alpha-tocopherol: × 0.67 (1 mg = 1.49 IU)
Synthetic all-rac-alpha-tocopherol: × 0.45 (1 mg = 2.22 IU)
- RRR
- the single naturally occurring stereoisomer, and the only one retained by hepatic alpha-tocopherol transfer protein
- all-rac
- an equimolar mixture of eight stereoisomers, of which only the four 2R forms are retained — hence the lower factor
- esters
- acetate and succinate esters are hydrolysed in the gut and absorbed as efficiently as free alpha-tocopherol, so the same factors apply
Worked example
400 IU of natural RRR-alpha-tocopherol (d-alpha)
Natural factor = 0.67 mg per IU
400 × 0.67 = 268.0 mg alpha-tocopherol
The same 400 IU as the synthetic form would be 400 × 0.45 = 180.0 mg
Common supplement doses converted
| IU | Natural (d-alpha), mg | Synthetic (dl-alpha), mg |
|---|---|---|
| 100 | 67 | 45 |
| 200 | 134 | 90 |
| 400 | 268 | 180 |
| 800 | 536 | 360 |
| 1,000 | 670 | 450 |
Adult reference values
| mg/day | IU, natural | IU, synthetic | |
|---|---|---|---|
| RDA, adults | 15 | 22 | 33 |
| Tolerable upper intake level | 1,000 | 1,490 | 2,220 |
Natural and synthetic vitamin E are not interchangeable
The international unit for vitamin E was defined against the synthetic form, so 1 mg of all-rac-alpha-tocopherol equals 2.22 IU and 1 IU equals 0.45 mg. Natural RRR-alpha-tocopherol is more potent: 1 mg equals 1.49 IU, so 1 IU equals 0.67 mg. A 400 IU capsule is therefore 268 mg if it contains the natural form and 180 mg if it contains the synthetic one, a difference large enough to change where a total intake sits against the 1,000 mg upper limit.
The reason for the difference is stereochemistry. Alpha-tocopherol has three chiral centres, and only the RRR configuration occurs naturally. The synthetic material is an equimolar mixture of all eight stereoisomers, of which only the four 2R forms are bound and retained by hepatic alpha-tocopherol transfer protein — the carrier that loads alpha-tocopherol into very-low-density lipoprotein for export to the tissues. The 2S isomers are largely excreted, so roughly half the synthetic material never reaches the circulation in useful quantity.
Two further points affect how a label is read. Acetate and succinate esters, used because free alpha-tocopherol oxidises readily, are hydrolysed in the gut and absorbed about as efficiently as the free vitamin, so the same conversion factors apply to them. And only alpha-tocopherol meets the human requirement: gamma-tocopherol, the predominant form in the American diet, and the tocotrienols are not retained by the transfer protein and do not count towards the RDA, so a mixed-tocopherol product may supply less usable vitamin E than its total milligram figure suggests.
The upper limit exists because high-dose vitamin E has been associated with harm rather than benefit. A meta-analysis of supplementation trials found increased all-cause mortality at doses above about 400 IU daily, the SELECT trial found an increased incidence of prostate cancer, and vitamin E potentiates warfarin and increases the risk of haemorrhagic stroke. Frank deficiency is rare outside fat malabsorption, abetalipoproteinaemia and ataxia with isolated vitamin E deficiency, so high-dose supplementation in an otherwise well adult has no established indication.
Frequently asked questions
How many mg is 400 IU of vitamin E?
268 mg if the product contains natural RRR-alpha-tocopherol (d-alpha), or 180 mg if it contains the synthetic all-rac form (dl-alpha). Check the label, because the two are not interchangeable.
Why is natural vitamin E more potent than synthetic?
Hepatic alpha-tocopherol transfer protein selectively retains the 2R stereoisomers. Natural vitamin E is entirely RRR-alpha-tocopherol, while the synthetic form is a mixture of eight stereoisomers, only half of which are retained.
Do the same factors apply to tocopheryl acetate?
Yes. The acetate and succinate esters are used for stability, are hydrolysed in the intestine, and are absorbed about as efficiently as free alpha-tocopherol, so the natural and synthetic factors apply unchanged.
Does gamma-tocopherol count towards the vitamin E requirement?
No. Only alpha-tocopherol meets the human requirement, because the other tocopherols and the tocotrienols are not retained by alpha-tocopherol transfer protein. A mixed-tocopherol supplement can therefore supply less usable vitamin E than its total figure implies.
Is high-dose vitamin E harmful?
The tolerable upper intake level is 1,000 mg/day for adults. High-dose supplementation has been associated with increased all-cause mortality and haemorrhagic stroke, and with an increased incidence of prostate cancer in the SELECT trial; it also potentiates warfarin.
Related calculators
References
- National Institutes of Health, Office of Dietary Supplements. Vitamin E: Fact Sheet for Health Professionals. Bethesda, MD: NIH ODS.
- Institute of Medicine. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. National Academies Press; 2000.
- Miller ER 3rd, Pastor-Barriuso R, Dalal D, et al. Meta-analysis: high-dosage vitamin E supplementation may increase all-cause mortality. Ann Intern Med. 2005;142(1):37–46.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.