Vitamin E IU to mg: how to convert natural and synthetic vitamin E

400 IU of vitamin E is 268 mg if the form is natural and 180 mg if it’s synthetic. That’s almost a 1.5-fold difference, so find the form first and convert second:

For vitamins D and A, use the general IU to mcg and mg converter. This page sticks to vitamin E and goes into more detail.

Vitamin E IU to mg chart: 100 to 1,000 IU

The NHS puts the daily need at 4 mg for men and 3 mg for women, and says you should be able to get it from your diet. US figures are higher, at 15 mg for adults. Even so, NIH ODS notes that most vitamin-E-only supplements contain at least 67 mg (100 IU of the natural form), which is more than four times the US amount.

d-alpha vs dl-alpha tocopherol: natural and synthetic vitamin E

Natural alpha-tocopherol is a single molecule with one particular shape (RRR). Synthetic alpha-tocopherol is an equal mix of eight stereoisomers: molecules with the same atoms arranged in different shapes in space, rather like left and right mittens. Your blood and tissues keep only four of the eight, so, according to NIH ODS, a milligram of the synthetic form is about half as active as a milligram of the natural one. FDA labelling rules count it the same way: 1 mg of vitamin E on a label is 1 mg of natural alpha-tocopherol or 2 mg of synthetic. That’s where 0.67 and 0.45 come from. Both give the milligrams of vitamin E that count towards your needs, not the weight of the ingredient in the softgel.

A prefix in the ingredients tells you which one you have:

• d-alpha tocopherol or RRR-alpha-tocopherol – natural;
• d-alpha tocopheryl acetate or succinate – also natural, as an ester;
• dl-alpha tocopherol, all-rac-alpha-tocopherol or dl-alpha tocopheryl acetate – synthetic.

Esters (acetate and succinate) help vitamin E keep longer on the shelf. Your body splits and absorbs them as well as the plain tocopherol, and the FDA converts them with the factor of their form. If the front of the bottle only says “400 IU”, turn it round: the form is in the Supplement Facts panel.

400, 800 and 1,000 IU of vitamin E in mg

400 IU is 268 mg of the natural form or 180 mg of the synthetic form. Those are the doses used in two large trials that NIH ODS describes: HOPE gave 400 IU of natural vitamin E (268 mg), and SELECT gave 400 IU of synthetic dl-alpha-tocopheryl acetate (180 mg).

800 IU works out at 536 or 360 mg, and 1,000 IU at 670 or 450 mg. Both sit above EFSA’s limit, so they’re not doses to take for months without medical advice. Our guide to vitamins A and E covers the risks of high doses.

Upper limits: NHS, EFSA and the US

Each body counts vitamin E slightly differently, so comparing them in IU is easiest:

• NHS – taking 540 mg (800 IU) or less a day of vitamin E supplements is unlikely to cause any harm.
• EFSA – 300 mg a day for adults, including in pregnancy and breastfeeding; lower for children, from 100 mg at ages 1–3 to 260 mg at 15–17. EFSA counts vitamin E as alpha-tocopherol equivalents, and the report behind its limit pairs 800 IU with 537 mg. On that basis 300 mg is about 450 IU. EFSA is currently reviewing this limit.
• US (NIH) – 1,000 mg a day for adults, which NIH gives as 1,500 IU of the natural form or 1,100 IU of the synthetic form.

Why 1,100 and not 2,222 (1,000 ÷ 0.45)? The US limit counts the full weight of synthetic vitamin E, all eight stereoisomers, not only the four that count towards your needs. Use 0.45 to compare a dose with daily needs; for the limit, NIH does its own IU conversion.

When high doses matter: anticoagulants

Large doses of vitamin E taken with warfarin or other anticoagulant or antiplatelet medicines can raise the risk of bleeding, especially if your diet is low in vitamin K (NIH ODS). EFSA is explicit that its 300 mg limit doesn’t apply to people on anticoagulants or to people with malabsorption. The same report notes that vitamin E can increase the risk of bleeding in people who take aspirin.

Speak to your GP or anticoagulation clinic before the first softgel if:

1. you take warfarin, another anticoagulant or daily aspirin;
2. you have a condition that affects fat absorption, or a bowel disease;
3. you’re having surgery: a source cited in the EFSA report suggests avoiding high doses (800–1,200 mg alpha-tocopherol equivalents) for two weeks before and after an operation;
4. you’re pregnant or breastfeeding and want more than your pregnancy vitamin already gives.

Our page on supplements and medicines helps with other prescriptions, and the vitamin compatibility chart covers combinations of supplements.

How to choose vitamin E on iHerb

1. Find the Vitamin E line in the Supplement Facts panel: it gives the dose in mg and the form in brackets.
2. Use the d- or dl- prefix to tell natural from synthetic.
3. If the bottle only shows IU, convert with the calculator above.
4. Add up the vitamin E from every supplement you take: multivitamin, omega-3, skin formulas.
5. For daily use, stay at or below 400 IU (268 mg of the natural form).
6. For the rest of the panel, see how to read a supplement label; for why IU exist at all, see what an IU on a vitamin label means.

Vitamin D is simpler, with one factor for every form: see vitamin D mcg to IU.