Is natural vitamin E better than synthetic?

Natural and synthetic forms

Natural vitamin E from plants is RRR-alpha-tocopherol, often labelled d-alpha-tocopherol.^[1] Synthetic vitamin E is all-rac-alpha-tocopherol, labelled dl-alpha-tocopherol. It contains equal amounts of 8 stereoisomers, molecules with the same atoms in different 3D shapes. Blood and tissues keep only 4 of them.^[1] So 1 mg of synthetic vitamin E is half as active as 1 mg of natural vitamin E.^[1]

How to compare labels

New US labels give vitamin E in mg of alpha-tocopherol, and older labels used IU:^[1]

• 1 IU of natural vitamin E is 0.67 mg of alpha-tocopherol^[1]
• 1 IU of synthetic vitamin E is 0.45 mg of alpha-tocopherol^[1]
• the adult daily need of 15 mg is 22.4 IU of the natural form or 33.3 IU of the synthetic form^[1]

What studies of the two forms found

Studies in people and animals used vitamin E labelled with deuterium, a heavy form of hydrogen, to follow each form in the body. They found that the natural form is about twice as potent as the synthetic form (2 to 1). The older official ratio was 1.36 to 1.^[2] The US recommended amounts now use the 2 to 1 ratio: 1 mg of vitamin E is 1 mg of the natural form or 2 mg of the synthetic form.^[1]

Acetate and succinate

Many supplements contain alpha-tocopherol bound to acetate or succinate. These esters keep longer on the shelf. The body splits them and absorbs them as well as plain alpha-tocopherol.^[1] A label such as d-alpha-tocopheryl acetate means the natural form, and dl-alpha-tocopheryl acetate the synthetic form.^[1]

Other tocopherols and tocotrienols

Some products also contain other tocopherols and tocotrienols.^[1] The liver sends mainly alpha-tocopherol into the blood and breaks down the other forms, so their levels in blood and cells are lower and they are less studied.^[1] US and EU intake values count only alpha-tocopherol.^[1][3]

Upper limits count both forms

The US upper limit applies to every form of alpha-tocopherol in supplements, including all 8 stereoisomers of the synthetic form.^[1] The EU upper limit also applies to all of them.^[4] For adults, the US limit of 1,000 mg a day is 1,500 IU of the natural form or 1,100 IU of the synthetic form.^[1] Of the 8 synthetic forms, the 4 called 2S forms are poorly available to the body and add very little vitamin E activity.^[2]

Which form the large trials used

Trials used both forms. HOPE and the Women's Health Study gave natural vitamin E.^[5][6] SELECT and AREDS gave synthetic vitamin E as dl-alpha-tocopheryl acetate.^[7][1] Neither form lowered major heart events: HOPE and the Women's Health Study gave the natural form, and the Physicians' Health Study II gave the synthetic form.^[5][6][8][1]