Saturday, September 03, 2005

Vitamin E as Antioxidant

Vitamin E is also known as Tocopherol. Alpha-tocopherol is traditionally recognized as the most active form of vitamin E in humans, and is a powerful antioxidant. The measurement of "vitamin E" activity in international units (IU) was based on fertility enhancement by the prevention of spontaneous abortions in pregnant rats relative to alpha tocopherol. It increases naturally to about 150% of normal in the maternal circulation during human pregnancies. The other isomers are slowly being recognized as research begins to elucidate their additional roles in the human body. Many naturopathic and orthomolecular medicine advocates suggest that vitamin E supplements contain at least 20% by weight of the other natural vitamin E isomers. Commercially available blends of natural vitamin E include "mixed tocopherols" and "high gamma tocopherol" formulas. Also selenium, Coenzyme Q10, and ample vitamin C have been shown to be essential cofactors of natural tocopherols.

Antioxidants such as vitamin E act to protect cells against the effects of free radicals, which are potentially damaging by-products of the body's metabolism. Free radicals can cause cell damage that may contribute to the development of cardiovascular disease and cancer. Vitamin C and other anti-oxidants recycle vitamin E end-products back into effective suppressors of free radicals. Studies are underway to determine whether vitamin E might help prevent or delay the development of those chronic diseases.

Vegetable oils, nuts, wheat germ and green leafy vegetables are the main dietary sources of vitamin E. Fortified breakfast cereals are also an important source of vitamin E in the United States. Although originally extracted from wheat germ oil, most natural vitamin E supplements are now derived from vegetable oils, usually soybean oil.

Commercial vitamin E supplements can be classified into several distinct categories: fully synthetic vitamin E, "d,l-alpha-tocopherol", the most inexpensive, most commonly sold supplement form usually as the acetate ester; semisynthetic "natural source" vitamin E esters, the "natural source" forms used in tablets and multiple vitamins; highly fractionated natural d-alpha tocopherol; less fractionated "natural mixed tocopherols"; high gamma-tocopherol fraction supplements; and tocotrienol supplements.

Synthetic vitamin E, usually marked as d,l-tocopherol or d,l tocopheryl acetate, with 50% d-alpha tocopherol moiety and 50% l-alpha-tocopherol moiety, as synthesized by an earlier process is now actually manufactured as all-racemic alpha tocopherol, with only about one alpha tocopherol molecule in 8 molecules as actual d-alpha tocpherol. The synthetic form is not as active as the natural alpha tocopherol form. The 1950's thalidomide disaster with numerous severe birth defects is a common example of d- vs l- epimer forms type problem with synthesized racemic mixtures. Information on any side effects of the synthetic vitamin E epimers is not readily available. Naturopathic and orthomolecular medicine advocates have long considered the synthetic vitamin E forms to be with little or no merit for cancer, circulatory and heart diseases.

Semisynthetic "natural source" vitamin E, manufacturers convert the common natural beta, gamma and delta tocopherol isomers into esters using acetic or succinic acid and add methyl groups to yield d-alpha tocopheryl esters such as d-alpha tocopheryl acetate or d-alpha tocopheryl succinate. These tocopheryl esters are more stable and are easy to use in tablets and multiple vitamin pills. Because only alpha tocopherols were officially counted as "vitamin E" in supplements, refiners and manufacturers faced enormous economic pressure to esterify and methylate the other natural tocopherol isomers, d-beta-, d-gamma- and d-delta-tocopherol into d-alpha tocopheryl acetate or succinate. In the healthy human body, the semisynthetic forms are easily de-esterified over several days, primarily in the liver, but not for common problems in aged or ill patients.