Natural and synthetic vitamin E: how do they differ?

Natural and synthetic vitamin E differ in the spatial arrangement of the molecule, not in its formula. Natural alpha-tocopherol, which plants make, is a single form called RRR-alpha-tocopherol, commonly written as d-alpha-tocopherol. Synthetic alpha-tocopherol, made by chemical synthesis, is all-rac-alpha-tocopherol, written as dl-alpha-tocopherol: an equal mixture of eight stereoisomers. Both have the formula C29H50O2. Beyond alpha-tocopherol, vitamin E also includes other tocopherols and tocotrienols, which differ in their tail and in the number of methyl groups on their ring.

In short:

• Natural (d-alpha): RRR-alpha-tocopherol, one stereoisomer, made by plants
• Synthetic (dl-alpha): all-rac-alpha-tocopherol, eight stereoisomers in equal amounts, made by chemical synthesis
• Tocopherols and tocotrienols: same ring, different tail (saturated, or with three double bonds)
• Alpha, beta, gamma, delta: three, two, two or one methyl group on the ring
• Daily amount: Thai RDI 9 mg α-TE

This article explains the structure, origin and definitions of each form of vitamin E. For how much vitamin E foods contain, see Which foods are high in vitamin E, and how much?

What is vitamin E made of?

Vitamin E is not one molecule but a family. The NIH Office of Dietary Supplements (ODS) says naturally occurring vitamin E exists in eight chemical forms: alpha-, beta-, gamma- and delta-tocopherol, and alpha-, beta-, gamma- and delta-tocotrienol.

A ring and a tail

A 2017 review from the University of Fribourg in Switzerland explains that these compounds belong to a chemical family called tocochromanols: molecules with a polar chromanol ring and a fat-loving side chain, or tail. The review notes that tocochromanols are made mostly by plants, algae and some cyanobacteria, and that edible plant products, especially seed oils, are the main sources of vitamin E in the human diet.

How do tocopherols and tocotrienols differ?

They share the same ring and differ in the tail. The Fribourg review explains that the tail of tocopherols is built from phytyl pyrophosphate and the tail of tocotrienols from geranylgeranyl pyrophosphate. The result is visible in the chemical names in PubChem, the chemistry database of the US National Library of Medicine.

Source: Mène-Saffrané (2017) and PubChem. The three double bonds account for the six fewer hydrogen atoms in alpha-tocotrienol (H44 against H50).

Alpha, beta, gamma and delta

Within each family, the Greek letter tells you how many methyl groups sit on the ring. The Fribourg review lists three methyl groups for the alpha form, two for the beta and gamma forms, and one for the delta form. The positions below come from the chemical names in PubChem.

Beta and gamma have the same formula and differ only in where one methyl group sits. Every form also carries a methyl group at position 2, where the tail joins the ring, which is not counted here.

Where do the different forms occur in food?

Different plants store different forms, so the mix depends on the food.

Oils and nuts

In the US Department of Agriculture's FoodData Central (SR Legacy), which lists some forms separately:

Values in mg per 100 g; a dash means the database gives no value. Sunflower seeds are almost entirely alpha-tocopherol, soybean oil is mostly gamma and delta, and coconut oil has more alpha-tocotrienol than alpha-tocopherol. The Fribourg review describes the same grouping: sunflower and wheat seeds hold mostly the alpha form, while rapeseed and maize hold both alpha and gamma forms.

Thai rice and rice bran

Rice is a source of tocotrienols. A study by the Thai Rice Department analysed 101 local rice varieties from north-eastern Thailand grown in the 2016 wet season and found that gamma-tocotrienol was the main form of vitamin E in every sample, with the other forms in small amounts.

A Chiang Mai University study measured tocopherols and tocotrienols together in rice bran and vegetable oil samples and found a wide range, from 22.4 to 1,774.6 µg per g. For the amounts in each rice variety and in rice bran oil, see Which foods are high in vitamin E, and how much?

How do natural and synthetic alpha-tocopherol differ?

Natural and synthetic alpha-tocopherol have the same atoms in the same order. What differs is the three-dimensional arrangement at the three stereocentres.

Natural: one form, RRR

PubChem's name for natural alpha-tocopherol, (2R)-2,5,7,8-tetramethyl-2-[(4R,8R)-4,8,12-trimethyltridecyl]-3,4-dihydrochromen-6-ol, specifies R at all three stereocentres, hence RRR-alpha-tocopherol. The ODS says naturally sourced vitamin E is called RRR-alpha-tocopherol, commonly written as d-alpha-tocopherol, and that naturally occurring alpha-tocopherol exists in one stereoisomeric form.

Synthetic: eight forms, all-rac

Each of the three stereocentres can be R or S, which gives eight possible combinations (RRR, RRS, RSR, RSS, SRR, SRS, SSR and SSS). The ODS says synthetically produced alpha-tocopherol, all-rac-alpha-tocopherol, commonly written as dl-alpha-tocopherol, contains equal amounts of its eight possible stereoisomers. Its PubChem entry, DL-alpha-tocopherol, has the same formula and molecular weight as the natural form (C29H50O2, 430.7 g/mol) but no R or S in its name.

Natural and synthetic side by side

A 2024 review from Zhejiang University describes the two established routes of production, chemical synthesis and plant extraction, and notes that chemical synthesis cannot produce a specific stereoisomer, while extraction from plants yields natural vitamin E. The review also describes newer work on producing vitamin E with engineered microorganisms.

What are tocopheryl acetate and tocopheryl succinate?

The ODS says alpha-tocopherol in dietary supplements and fortified foods is often esterified to prolong its shelf life. In an ester, the hydroxyl group at position 6 of the ring is joined to an acid.

What units are used for vitamin E?

Vitamin E used to be measured in international units (IU). The ODS says that in the United States vitamin E has been listed in milligrams rather than IU since 2020.

mg α-TE in the Thai RDI

The Thai Reference Daily Intake (Thai RDI) for vitamin E is expressed in mg α-TE, or alpha-tocopherol equivalents, and is 9 mg α-TE a day for the general population aged 3 and over. For the other Thai RDIs, see What are the Thai daily reference amounts for each nutrient?

How much vitamin E is too much?

The ODS says research has not found any adverse effects from consuming vitamin E in food. The US Tolerable Upper Intake Level for adults is 1,000 mg a day, and the ODS says the upper limits apply to all forms of supplemental alpha-tocopherol, including the eight stereoisomers in synthetic vitamin E.

The ODS says these limits were set because of the potential for effects on bleeding. Vitamin E can come from more than one product, so the amounts add up.

Who should talk to a doctor or pharmacist?

People who take regular medication

The ODS says vitamin E supplements can interact with some medicines, including medicines that slow blood clotting. If you take medication regularly, ask a doctor or pharmacist before adding vitamin E.

Pregnant and breastfeeding women

If you are pregnant or breastfeeding, talk to a doctor or pharmacist before taking any dietary supplement, including vitamin E.

Dietary supplements are not intended to prevent, treat or cure any disease.