Vitamin E IU to mg
Natural vitamin E: 1 IU = 0.67 mg. Synthetic vitamin E: 1 IU = 0.45 mg. So 400 IU is 268 mg if the label says d-alpha-tocopherol, or 180 mg if it says dl-alpha-tocopherol.
| IU | Natural (d-alpha), mg | Synthetic (dl-alpha), mg |
|---|---|---|
| 100 IU | 67 | 45 |
| 200 IU | 134 | 90 |
| 400 IU | 268 | 180 |
| 800 IU | 536 | 360 |
| 1,000 IU | 670 | 450 |
The formula
natural (d-alpha): mg = IU × 0.67 IU = mg × 1.49 synthetic (dl-alpha): mg = IU × 0.45 IU = mg × 2.22
These factors are from the NIH Office of Dietary Supplements and convert to mg of alpha-tocopherol, the form the RDA is based on. The reverse factors are rounded by NIH (1 ÷ 0.67 is 1.4925); the converter divides by 0.67 or 0.45 directly, so it can differ from a hand calculation in the second decimal.
Why one number isn't enough
Most quick answers say "400 IU of vitamin E = 268 mg" or "= 180 mg" without saying which form. Both are right for one form and wrong for the other. Since the FDA's updated labelling rules, US labels give vitamin E in mg of alpha-tocopherol, so on a newer bottle you may not need to convert at all; older bottles and many foreign labels still use IU.
Recommended amounts and the upper limit
NIH's RDA for adults is 15 mg of alpha-tocopherol a day. The upper limit for adults is 1,000 mg a day from supplements, which NIH equates to 1,500 IU of natural or 1,100 IU of synthetic vitamin E. This page converts amounts; ask your clinician what's right for you, especially if you take blood thinners.
Questions
How many mg is 400 IU of vitamin E?
268 mg of natural vitamin E (d-alpha-tocopherol) or 180 mg of synthetic vitamin E (dl-alpha-tocopherol).
How do I know if my vitamin E is natural or synthetic?
Check the ingredient name. A "d-" prefix (d-alpha-tocopherol, d-alpha-tocopheryl acetate or succinate) is natural. A "dl-" prefix is synthetic.
How many IU is 15 mg of vitamin E?
15 mg, the adult RDA, is about 22.4 IU of natural vitamin E or 33.3 IU of synthetic.
Why are the two forms different?
Synthetic vitamin E is a mix of eight forms, and only some are active in the body, so it takes more of it to give the same activity. That's why 1 IU of synthetic weighs less in active alpha-tocopherol.