After decades of study, the specific role of vitamin E in a required metabolic function in the human body has yet to be found. On the other hand, in company with the vitamin A precursors (carotenoids) and vitamin C, vitamin E has antioxidant properties effective in the so-called “chain-breaking” of oxidizing agents in cellular tissue.
      Vitamin E is a compound made up of eight naturally occurring substances: alpha-, beta-, gamma-, and delta-tocopherol, and alpha-, beta-, gamma-, and delta-tocotrienol. Without delving into the biochemistry, because this can be somewhat complex, only alpha-tocopherol is retained in the body in any significant amount, and therefore the only form of vitamin E that is absorbed into the blood stream for transport to the tissues where it is utilized. This is the only active form of the vitamin in humans.

      In a manner similar to vitamin A, vitamin E has suffered somewhat of an identity crisis in the sense of how it is measured and quantified. Unlike vitamin A, however, understanding the equivalencies of vitamin E is considerably more complicated.
      For most visitors to our site, taking the conversion factors presented in the table below on faith will suffice. If you are interested in a more detailed explanation, we offer this additional information.
      Figures for the recent National Academy of Sciences Dietary Reference Intakes study are based upon slightly different age ranges, which accounts for the overlapping age groups.

      The primary sources of vitamin E are edible vegetable oils, and the various foods that contain vegetable oils. One example is nuts, especially almonds and, to a much lesser degree, pistachios, dry-roasted peanuts, and of course, peanut butter. Among the oils themselves, sunflower oil has the highest concentration, followed by safflower oil, canola oil, olive oil, and others. Other foods providing vitamin E include unprocessed cereals, whole-grain products, wheat germ, fruits, vegetables, liver, and meats, especially the fatty portion.
      Since many food labels do not indicate the specific fat or oil utilized when these substances are present, it is often difficult to accurately assess the total intake of dietary vitamin E.

      The most common occurrences of vitamin E deficiency are the result of specific medical conditions where individuals are unable to absorb fatty compounds, or rare genetic disorders that interfere with the maintenance of normal blood concentrations of the vitamin. Although uncommon, various nervous system disorders have been known to occur in such cases. Ordinary diets are generally sufficient to prevent deficiencies leading to such conditions.

      The forms of supplemental vitamin E are numerous, and attempting to quantify any one of them can be very difficult. To complicate matters, the absorption of vitamin E (as alpha-tocopherol) varies considerably depending upon what other compounds with which it is ingested.
      Generally speaking, the synthetic forms of alpha-tocopherol are more concentrated when taken either as a standalone supplement (i.e., not as a multivitamin, or with dietary sources of natural alpha-tocopherol), or in combination with other antioxidants such as selenium, sulfur-amino acids, or vitamins A and C. Some of the synthetic forms of vitamin E commonly seen on labels include dl-alpha-tocopherol, racemic-alpha-tocopherol, rac-alpha-tocopherol, all racemic-alpha-tocopherol, and all rac-alpha-tocopherol. The tocopheryl acetate and tocopheryl succinate esters of alpha-tocopherol are generally equivalent.
      Dietary sources are generally sufficient for the normal intake of vitamin E. Exceptions occur in some individuals who have difficulty absorbing fat, such as those with liver disease. Because of its antioxidant properties, however, supplemental sources of alpha-tocopherol have been reported as having potential effects against heart disease and some cancers. As with the other antioxidants, there is much controversy and the positive effects of vitamin E in this regard are not yet clear.

      Vitamin E concentrations in the blood have been found to last for months, in part because this is a fat-soluble vitamin and not as easily excreted as water-soluble vitamins. Even so, there appears to be little or no risk from the consumption of large amounts of vitamin E from dietary sources.
      Extremely large doses of vitamin E from supplemental sources, however, have been implicated in some bleeding disorders. Individuals who also consume supplemental fish oil (omega-3, other fatty acids, and cod liver oil, in particular) are at greater risk due to a higher retention of fat soluble vitamins. The latest report from the National Academy of Sciences (NAS) study on Dietary Reference Intakes (DRI) has therefore recommended a tolerable upper intake level (UL) of 1000 mg/day of alpha-tocopherol (from supplements) as a safe level.

      There have been a number of large studies that have tested the ability of supplemental vitamin E (alpha-tocopherol) to decrease the risk of heart disease. The results have been mixed, and are far from conclusive. There is considerable evidence, however, that the oxidative process at the cellular level is involved in heart disease, so the effects of alpha-tocopherol as an antioxidant remain an important preventative measure in the possible prevention of cardiovascular disease.
      There have also been numerous studies that have investigated the role of vitamin E in the prevention of various cancers. These results are also mixed, but generally weaker overall than those for cardiovascular disease. Research in both areas, as well as for other disease processes, continues, and we plan to summarize this research over time as the potential effects of vitamin E in preventive health develop in greater depth.