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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).
Designed
and Developed by WF Team and updated on 1st November,
2001.
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