Evidence explainerVitamin E (natural d-alpha vs synthetic dl-alpha tocopherol)

400 IU of Vitamin E Is Either 268 mg or 180 mg. The "d" or "dl" on the Label Decides

Vitamin E labels switched from IU to mg, and the conversion depends on whether the vitamin is natural or synthetic. Here is the math, and what the difference does and does not mean.

By Kymata Health editorial teamPublished October 9, 2026Last reviewed October 9, 2026

Medical review pending. Written by our editorial team from the studies cited below; a credentialed clinician has not reviewed it yet. Educational only, not medical advice.

Key takeaways

  • One IU of natural vitamin E equals 0.67 mg of alpha-tocopherol; one IU of synthetic equals 0.45 mg [1].
  • So 400 IU is about 268 mg if natural (d-alpha-tocopherol) and 180 mg if synthetic (dl-alpha-tocopherol) [1].
  • Synthetic vitamin E is half as active per mg, because the body keeps only four of its eight forms [1].
  • The adult RDA is 15 mg/day; most vitamin E-only supplements provide 67 mg (100 IU natural) or more [1].
  • The upper limit is 1,000 mg/day, which is 1,500 IU natural or 1,100 IU synthetic [1].

Safety at a glance

From our Vitamin E (natural d-alpha vs synthetic dl-alpha tocopherol) monograph. Published interactions and cautions only, each with its source.

Interactions

  • Anticoagulants and antiplatelet drugs. Vitamin E can inhibit platelet aggregation and antagonize vitamin K-dependent clotting factors, raising bleeding risk at large doses, especially with low vitamin K intake. Clinically significant amounts are unknown but probably exceed 400 IU/day.[1]
  • Simvastatin plus niacin. An antioxidant combination containing vitamin E, vitamin C, selenium and beta-carotene blunted the rise in HDL cholesterol in people on simvastatin plus niacin.[1]
  • Chemotherapy and radiotherapy. Oncologists generally advise against antioxidant supplements during these treatments because they might reduce effectiveness; a systematic review questioned this, and more research is needed.[1]

Who should be careful

  • Bleeding risk. High-dose vitamin E may increase bleeding; two trials found more hemorrhagic stroke with alpha-tocopherol. People on blood thinners or antiplatelet drugs, or before surgery, should discuss vitamin E with a clinician.[1][4]
  • Men and prostate findings. 400 IU/day of synthetic vitamin E raised prostate cancer by 17% in the SELECT trial of healthy men.[5]
  • Cancer treatment. Oncologists generally advise against antioxidant supplements during chemotherapy or radiotherapy.[1]
  • Before you start. Talk to your pharmacist or clinician before adding this supplement, especially if you take prescription medicines, are pregnant or breastfeeding, or have a chronic health condition.[1]

Full Vitamin E (natural d-alpha vs synthetic dl-alpha tocopherol) safety section

The evidence, graded

Pulled from our monograph evidence tables. Grades follow our evidence-grading policy.

  • Grade BImprovedProstate outcome in healthy men (SELECT extended follow-up)Vitamin E (natural d-alpha vs synthetic dl-alpha tocopherol) · RCT · n=34,887 · 2011 · PMID 21990298Prostate cancer was 17% more common with vitamin E than placebo (HR 1.17; 99% CI 1.004-1.36): 620 vs 529 men, an absolute increase of 1.6 per 1000 person-years.
  • Grade CImprovedAll-cause mortality with high-dosage vitamin EVitamin E (natural d-alpha vs synthetic dl-alpha tocopherol) · Meta-analysis · n=135,967 · 2005 · PMID 15537682Trials of ≥400 IU/d showed 39 more deaths per 10,000 persons (95% CI 3 to 74); low-dosage trials showed no increase. Risk rose with dosages above 150 IU/d.

Reading the label: d vs dl

Natural vitamin E is RRR-alpha-tocopherol, usually labeled d-alpha-tocopherol. Synthetic vitamin E is all rac-alpha-tocopherol, usually labeled dl-alpha-tocopherol [1].

Many supplements use an ester such as alpha-tocopheryl acetate or succinate to extend shelf life. The body splits and absorbs these esters as efficiently as plain alpha-tocopherol, so "acetate" on the label is not a red flag [1].

The IU to mg conversion

Supplement Facts panels now list vitamin E in mg; FDA required the new labels from January 2020, with smaller companies allowed until January 2021, so older bottles may still show IU [1]. The conversions ODS gives:

  • 1 IU natural (d-alpha) = 0.67 mg alpha-tocopherol [1]
  • 1 IU synthetic (dl-alpha) = 0.45 mg alpha-tocopherol [1]
  • 400 IU natural = about 268 mg; 400 IU synthetic = about 180 mg [1]
  • 600 IU natural = about 402 mg [1]
  • 15 mg (the adult RDA) = 22.4 IU natural or 33.3 IU synthetic [1]

Is natural better than synthetic?

Per mg, yes. Synthetic alpha-tocopherol contains equal amounts of eight stereoisomers, and blood and tissues keep only four of them, so a given weight of synthetic vitamin E is half as active as the same weight of natural [1].

What "natural" does not buy you is a better outcome in trials. Large heart trials of natural vitamin E at 400 IU or more found no protection against major heart events [1], and the prostate cancer signal in SELECT came from synthetic vitamin E [2]; we cover the trials in vitamin E and the heart.

How much is too much?

Adults need 15 mg/day of alpha-tocopherol, 19 mg while breastfeeding [1]. Most vitamin E-only supplements provide 67 mg or more, well above that [1].

The upper limit for adults is 1,000 mg/day of supplemental alpha-tocopherol, set because of bleeding effects [1]. Lower amounts are not risk-free: a meta-analysis of 19 trials found more deaths in trials using 400 IU/day or more (39 more per 10,000 people), with risk rising above 150 IU/day [3]. ODS notes vitamin E can raise bleeding risk with warfarin and similar drugs, probably above 400 IU/day [1].

Mixed tocopherols and tocotrienols are sold too, but intake targets count alpha-tocopherol only, and the trials graded on the vitamin E monograph did not test them [1].

Quick answers

How many mg is 1,000 IU of vitamin E?

About 670 mg for natural and 450 mg for synthetic, using ODS factors of 0.67 and 0.45 mg per IU [1]. The adult upper limit is 1,000 mg/day, or 1,500 IU natural and 1,100 IU synthetic [1].

Is dl-alpha-tocopherol bad?

It is the synthetic form and is half as active per mg as the natural form [1]. The SELECT trial that found more prostate cancer used 400 IU/day of synthetic vitamin E, but the heart trials found no benefit with natural vitamin E either [2][1].

Do I need a vitamin E supplement?

The FNB suggests that mean intakes among healthy adults are probably above the RDA, though low-fat diets may fall short [1]. Nuts, seeds and vegetable oils are among the best food sources [1].

Keep reading

Full monographs

Related articles

Browse the full Supplement & Nutrient Encyclopedia or all supplement articles.

References

  1. [1]Vitamin E: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2021.
  2. [2]Vitamin E and the risk of prostate cancer: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA, 2011. PMID 21990298
  3. [3]Meta-analysis: high-dosage vitamin E supplementation may increase all-cause mortality. Ann Intern Med, 2005. PMID 15537682

Vitamin E (natural d-alpha vs synthetic dl-alpha tocopherol) and other dietary supplements are not intended to diagnose, treat, cure or prevent any disease, and these statements have not been evaluated by the FDA. Talk to your clinician or pharmacist before starting a supplement, especially if you take prescription medicines. This page has no product or affiliate links.

Keep reading: Supplements and vitamins

Supplements and vitamins: every page →Supplement & Nutrient Encyclopedia →Browse all topics →

Previous in this topicZinc (picolinate vs gluconate vs bisglycinate)Zinc is an essential trace mineral needed by hundreds of enzymes, for immune function, protein and DNA synthesis, and growth.Next in this topicAlpha-GPC vs Choline Bitartrate: Blood Choline Rose the Same, but One Detail DifferedAlpha-GPC is sold as the premium choline.Ashwagandha for Stress and Sleep: What the Trials Found, and Why the Results Vary So MuchAshwagandha is the internet’s favorite calm-down herb.B12 After 50 and on Metformin: Why Levels Drop, and What the Trials Say About Fixing ThemAbsorbing B12 gets harder with age, and two of the most prescribed drug types make it harder still.Berberine Side Effects and Drug Interactions: The Liver-Enzyme Problem Nobody MentionsBerberine’s stomach side effects are well known.

Evidence-graded supplement stacks →