Vitamin E is the collective term given
to a group of fat-soluble compounds first
discovered in 1922 by Evans and Bishop;
these compounds have distinct antioxidant activities
essential for health.1
Vitamin E is present in fat-
containing foods2
and, as the fat-soluble property of the
vitamin allows it to be stored within the fatty tissues of
animals and humans, it does not have to be consumed
every day. The vitamin E group (i.e. chroman-6-ols),
collectively termed tocochromanols (divided into
tocopherols and tocotrienols), includes all of the tocol
and tocotrienol derivatives which qualitatively exhibit
the biological activity of d-alpha-tocopherol.
There are eight naturally occurring forms of
vitamin E; namely, the alpha, beta, gamma and delta
classes of tocopherol and tocotrienol, which are
synthesised by plants from homogentisic acid. Alpha-
and gamma-tocopherols are the two major forms of
the vitamin, with the relative proportions of these
depending on the source. The richest dietary sources
of vitamin E are edible vegetable oils as they contain
all the different homologues in varying proportions
[Table 1]. Among the tocopherols, the alpha- and
gamma-tocopherols are found in the serum and the
red blood cells, with alpha-tocopherol present in the
highest concentration.3
Beta- and delta-tocopherols
are found in the plasma in minute concentrations only.
The preferential distribution of alpha-tocopherol in
humans over the other forms of tocopherol stems from
the faster metabolism of the other forms and from
the alpha-tocopherol transfer protein (alpha-TTP). It
is due to the binding affinity of alpha-tocopherol with
alpha-TTP that most of the absorbed beta-, gamma-
and delta-tocopherols are secreted into the bile and
excreted in the faeces, while alpha-tocopherol is largely
excreted in the urine. The alpha-tocopherol form also
accumulates in the non-hepatic tissues, particularly
at sites where free radical production is greatest,
such as in the membranes of the mitochondria and
endoplasmic reticulum in the heart and lungs.
This review mainly focuses on the current
developments in vitamin E research in the context
