Vitamin E

The Difference between Tocopherols and Tocotrienols

Vitamin E is a collective term referring to a family of 8 molecular structures that consist of a chromanol "head" and side-chain "phytyl tail". Of these eight molecules, there are four tocotrienol isomers and four tocopherol isomers. While the "heads" of the respective alpha, beta, gamma, and delta tocopherols and tocotrienols are the same, they differ in the chemical nature of the side chain or "tail". Tocopherols and tocotrienols have distinct bio-activity and function. Although it is generally believed that there are only four tocopherols and four tocotrienols in nature, there are at least 12 known E vitamins, including two new tocopherols and two new tocotrienols, and this number is likely to increase in the future.

Tocopherols hinder the assimilation of tocotrienols in the body

One might expect that in nature we would find the complete vitamin E family of tocopherols and tocotrienols together in various plants, but this is not the case. Plants actually widely differ in their vitamin E proportions, and no single plant provides the entire vitamin E family. This little-known fact changes the way we look at "naturally occurring" vitamin E and has important implications in vitamin E supplementation. Current research has confirmed several significant facts about the body's assimilation of tocopherols and tocotrienols. Tocopherols, mainly alpha tocopherol, hinder the assimilation of tocotrienols in the human body. This is due to the preferential uptake of tocopherol via the tocopherol-transfer protein which discriminates between tocopherols and tocotrienols. Thus, combining them together, as some supplement companies do, does not appear to be efficacious.

Optimal Supplementation includes the entire Vitamin E complex - with tocopherols ingested hours apart from tocotrienols, as tocopherols hinder the assimilation of tocotrienols in the human body.

Over-emphasis of alpha-tocopherol

Over-emphasis of alpha-tocopherol at the expense of the rest of the vitamin E complex is a result of several factors including:

Its introduction to the general public as the first vitamin E with its unique antioxidant properties and prevalence in the human body that permeated the popular and scientific literature.
Excessive IU claims motivated by market-driven sales.
The disconnect in the definition of RDA (based on the destruction of the membrane of red blood cells and/or rat fetal bone loss assay), leading to confusion in the perceived antioxidant value.

As a result, until recently, the tocotrienol portion of the vitamin E family has not been widely discussed.

Desmethyl Tocotrienols

Alpha-tocopherol should be de-emphasized and a higher priority be given to desmethyl vitamin Es, especially desmethyl tocotrienols, whose therapeutic functions are unshared by or superior to alpha-tocopherol. Additionally, alpha-tocotrienol is 5-fold less potent than the desmethyl tocotrienols.

Desmethyl tocotrienols have only one or no methyl group on the 6-hydroxychromane nucleus. It was shown that they have much greater antioxidant, hypocholesterolemic and antitumor properties than the other components of vitamin E.

Desmethyl tocotrienols significantly lowered serum total and LDL cholesterol levels and inhibited HMG-CoA reductase activity. They had much greater in vitro antioxidant activities and greater suppression of B16 melanoma cell proliferation than alpha-tocopherol and known tocotrienols.

Compositional Variation of Vitamin E

There is a lack of understanding regarding today's "tocotrienol products." These mixtures are often labeled as tocotrienol-rich fraction (TRF) or full spectrum vitamin E, without regards to the desmethyl tocotrienols. Also, alpha-tocopherol content varies widely. For example, rice and palm "tocotrienols" may contain 25-50% tocopherols, most of which (70 to 90%) is alpha-tocopherol. This is further confounded in that alpha-tocopherol decreases the concentration of alpha-tocotrienol.

To summarize, these commercially available TRFs are not uniform, contain little to no delta-tocotrienol, and are especially high in alpha tocotrienol. Additionally, because the variations are not properly understood, trade journals often combine the different vitamin Es when reporting on research results.

Many "full spectrum" vitamin E products keep the 400 IU (267 mg as RRR- or d-alpha-tocopherol) with about 100 to 200 mg of gamma-tocopherol, and small amounts of tocotrienols (e.g., 5-10 mg).

These "full-spectrum" vitamin formulations are neither consistent with current science nor a reflection of the US diet.

Differences Between Tocopherols and Tocotrienols

Recent research suggests that tocotrienols serve as antioxidants and also have important non-antioxidant functions such as lowering LDL cholesterol levels, preventing cell adhesion in certain cells and suppressing tumor growth.

Research in the past decade shows the commonly used alpha-tocopherol and alpha-tocotrienol do not share the beneficial effects of desmethyl tocotrienols. Research also shows that high levels of alpha-tocopherol may attenuate the bioavailability and functional activity of other vitamin E isomers. In general, desmethyl tocotrienols are much more bioactive than desmethyl tocopherols, especially in cancer inhibition.

Desmethyl tocotrienols are more bioavailable than non-desmethyl tocotrienols and tocopherols.
Tocopherols are inactive in inhibiting cholesterol synthesis.
Delta-tocotrienol improves vascular functions, reducing adhesion molecules over that of alpha-tocotrienol.
Tocotrienols inhibit angiogenesis (important in tumor growth, diabetic retinopathy, rheumatic arthritis, wet-type macular degeneration) via VEGF inhibition.
Delta-tocotrienol and, secondarily, gamma-tocotrienol correct for genetic defects in nerve protein synthesis in children with Familial Dysautonomia, a neurodegenerative genetic disorder.
Tocotrienols at concentrations well below their antioxidative properties (4-10x lower) are effective in preventing glutamate-induced neuronal cell deaths.
Gamma-tocotrienol and alpha-tocotrienol preferentially accumulate in adipose tissue and skin to a similar extent or higher than alpha-tocopherol.
Other unique effects of tocotrienols, especially the desmethyl isomers, not shared by alpha-tocopherol are natriuresis (the excretion of an excessively large amount of sodium in the urine), anti-hypertension, anti-inflammation and anti-osteoporosis.

Conclusions

There is a prevailing bias towards alpha-tocopherol as vitamin E given the absence of tocotrienols in published composition data. Each of the four commonly occurring isomers of tocotrienols and of tocopherols exhibits varying degrees of activity and efficacy. The generalized order of potency for tocotrienol is: delta-tocotrienol> gamma-tocotrienol >alpha-tocotrienol, and that of the tocopherols is desmethyl tocopherols > alpha-tocopherol.

This potency ranking holds true for indications including cancer inhibition, endothelial functions (i.e., inhibition of platelet aggregation and adhesion molecules), nerve function correction/protection, anti-angiogenesis, sodium excretion and anti-hypertension.

In addition to potency, an "appropriate spectrum" vitamin E must also consider application specific synergism and interference existing among the various vitamin E isomers.

References

Information here is taken from Appropriate Spectrum Vitamin E and New Perspectives on Desmethyl Tocopherols and Tocotrienols. Barrie Tan. Jana 35 Vol. 8, No. 1, 2005.