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Comparison of Natural and Synthetic Vitamin E
INTRODUCTION:
Vitamin E is the major chain-breaking antioxidant in body tissues and is
considered the first line of defense against lipid peroxidation, protecting cell
membranes at an early stage of free radical attack through its free
radical-scavenging activity. Unless scavenged by an antioxidant, highly unstable
free radicals attack the polyunsaturated fatty acids of cell membranes in a
chain reaction. Extensive evidence implicates free radicals in the development
of a number of degenerative diseases and conditions, including coronary heart
disease, cancer, Alzheimer's disease, arthritis, premature against and
cataracts.
Results of a number of studies suggest that increased vitamin E intakes are
associated with decreased risk of coronary heart disease and certain types of
cancer as well as enhancement of immune function. These increased vitamin E
intakes (100 I.U. and above) are considerably above levels obtainable from diet
alone, unless a very high-fat diet is consumed, as most foods high in vitamin E
are also high in fat.
Vitamin E is the exception to the paradigm that natural and synthetic
vitamins are equivalent because their molecular structures are identical.
Natural vitamin E (d-alpha-tocopherol) is a single stereoisomer and is derived
from vegetable oils, primarily soyabean, sunflower and corn oils. Synthetic
vitamin E (dl-alpha tocopherol) is produced commercially by a chemical reaction
of trimethylhydroquinone (TMHQ) with isophytol, resulting in a mixture of eight
stereoisomers in equal amounts. Only one of the stereoisomers, constituting only
12.5% of the total mixture, is d-alpha-tocopherol. The other seven stereoisomers
have different molecular configurations and biological activities that range
from 21-90% of the activity of natural vitamin E based on rate fetal resorption
tests.
The bio-availability of natural forms of vitamin E is higher than that of
synthetic forms, based on the animal assays and also demonstrated in human
studies. It appears that this discrimination occurs after absorption from the
digestive tract and that natural vitamin E is retained significantly longer in
body tissues.
HUMAN STUDIES:
A number of studies in human subjects have also compared the
bio-availability of natural and synthetic vitamin E.
A study of five human subjects confirms earlier findings in animals showing
a discrimination between d- and dl-alpha tocopherol. Following ingestion of 50
mg each of deuterated d-alpha-and dl-alpha tocopheryl acetate, plasma
concentrations of the two forms were similar until 11 hours when the d-alpha-tocopherol
level became significantly greater. By day one, red blood cells and plasma were
enriched 4 fold with d-alpha-tocopherol and the ratio of d- to dl-alpha
tocopherol further increased over the next four days because the dl stereoisomer
decreased at a faster rate than d-alpha-tocopherol.
The researchers stated that this study provides the first evidence that
humans strongly discriminate between the naturally occurring d-alpha-tocopherol
form of vitamin E and dl-alpha tocopherol. It appears that this discrimination
does not occur during absorption, but rather as a post-absorptive phenomenon in
the liver.
Using an equimolar concentration of deuterated natural and synthetic vitamin
E acetate, a recent study compared plasma vitamin E levels in healthy volunteers
and plasma and tissue vitamin E levels from elective surgery patients and from
terminally ill patients at autopsy. In healthy volunteers, the ratio of natural
to synthetic vitamin E in plasma ranged from 1.5 to 1.8 during 8 days of
supplementation and increased to 2.0 after supplementation ended. The ratio of
natural to synthetic vitamin E was 2.06 in plasma and1.71 in tissues of a
terminally ill patient supplemented for 361 days, and 2.11 in plasma and 2.01 in
tissues of a terminally ill patient supplemented for 625 days. The researchers
concluded that the bio-availability of synthetic vitamin E is approximately
one-half that of natural vitamin E.
SUMMARY:
For women who choose to supplement their diets to increase their intake of
vitamin E, a consideration of differences in bio-availability of natural and
synthetic vitamin E compounds is relevant. A number of studies have demonstrated
a strong discrimination between natural and synthetic vitamin E and that natural
vitamin E is retained longer in body tissues. The researches suggest that the
bio-availability of natural vitamin E is approximately twice that of synthetic
Vitamin E compounds.
Next time, you decide to take a Vitamin E supplement ask your doctor to
prescribe you a "natural" Vitamin E supplement for optimal health benefit .Also
to identify a type of Vitamin E in a supplement look at the product label .
Natural Vitamin E begins with "d" as in "d-alpha-tocopherol" while synthetic
vitamin E begin with "dl" (dl-alpha-tocopherol).
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