Vitamin C Scavenges Poisonous
Free Radicals
It is
astonishing how long the
list has become of substances
toxic to health. Even apart
from the environmentally
derived poisons including
lead from auto emissions,
pesticides, nitrates, ozone,
radioactive exposure, mercury
from dental fillings, PCB's,
etc., it is also true that
many natural processes and
substances vital to life
and health can also do us
in. Including, amazingly,
oxygen, the breath of life.
In the
words of Etsuo Niki, contributing
scientist from University
of Tokyo at the recently
held NY Academy of Science
Conference on Vitamin C(161),
"oxygen is a double-edged
sword. We cannot live without
oxygen, but at the same
time we are continuously
exposed to oxygen toxicity......the
free radical mediated peroxidation
of biological molecules
and tissues have received
much attention in connection
with a variety of pathological
events such as heart disease,
rheumatoid arthritis, inflammatory
disorders, cancer and even
the aging process".
This is the introduction
to Niki's elegant research
paper describing the synergistic
action of Vitamins C and
E in combating toxic oxygen
species.
What then
are "free radicals"
and "toxic oxygen species"?
Why are they so dangerous?
And what is Vitamin C's
role in neutralizing and
destroying these toxic species?
Free radical
oxygen species, some of
which are toxic, are highly
reactive, unstable molecules
because they have lost an
electron. Examples include
hydrogen peroxide, superoxide,
hydroxyl radical and singlet
oxygen. In the chemical
drive to replace that missing
electron, free radicals
may initiate an entire cascade
of chemical reactions, resulting
in damage to membranes,
DNA mutations, accelerated
ageing, disruptions in cell
vitality and function, and
deposition of fat. Reactant
oxidant species are thought
to underlie the cause of
many diseases; the use of
natural anti-oxidants is
widely advocated in the
treatment and detoxification
from such conditions(101).
Contrary
to what one might think,
free radicals are not always
externally derived; they
occur and are generated
in the body's natural biochemical
course of living and metabolism,
through the oxidation of
polyunsaturated fats, the
increased generation of
adrenalin and noradrenalin
under stress, and even as
toxic weapons used by phagocytes,
some of the foot soldiers
of the immune system. External
sources of free radicals
include exposure to low
levels of nuclear radiation
and electromagnetic emissions,
smog with its powerful oxidants
such as ozone, nitrogen
dioxide, and peroxyacyl
nitrates, cigarette smoke,
and environmental pollutant
drugs and chemicals(65).
Reassuringly,
however, there are a number
of natural substances, including
Vitamin C, which are powerful
anti-oxidants and free radical
scavengers, and which act
to prevent the damaging
effects of superoxides,
peroxides, hydroxyl radicals
and singlet oxygen molecules.
These include the preventative
antioxidants catalase and
peroxidase which decompose
peroxide without generating
free radicals, and chain-breaking
antioxidants which scavenge
radicals to stop free radical
and chain propagation reactions.
The water-soluble, aqueous
phase, chain-breaking antioxidants
include Vitamin C, uric
acid, cysteine and glutathione,
while the lipid soluble
antioxidants such as Vitamin
E function within membranes.
A list of toxic oxidants
and some of their known
respective scavengers is
presented in Table 3 below.
It is highly likely that
many more such natural scavengers
exist in nature, awaiting
our discovery.
Table 3. SOME ANTIOXIDANTS
FOR REACTIVE OXYGEN SPECIES
OXIDANT
SCAVENGER DIETARY ANTIOXIDANTS
Superoxide
Superoxide Dismutase(SOD)
Vitamin C, Rutin, Cysteine
Ceruloplasmin, Melanin,
Copper Complexes,
Alpha-mercaptopriopionyl
glycine
Hydrogen Peroxide Catalase,
Glutathione Vitamin C, Vitamin
E,
Uric Acid Selenium
Hydroxyl Radical Cholesterol,
Benzoate, Vitamin C, Rosemary,
Sage
Dimethyl Sulfoxide (DMSO)
Amygdalin, Anthocyanins
Formate, Uric Acid Cysteine
Singlet Oxygen Cholesterol,
Bilirubin Vitamin E, BHT,
Cholesterol
Histidine, Uric Acid Lemon
Oil, Beta-Carotene
(from "Oxidology"
Bradford, Allen & Culbert.
1985. Bradford Foundation(53))
Vitamin C scavenges superoxide
and hydroxyl radical(182),
as well as reacting directly
with hydrogen peroxide,
therefore protecting against
various toxic free radicals
which promote lipid peroxidation(33).
For example, the generation
of toxic oxygen species
by phagocytes is associated
with a number of chronic
degenerative and inflammatory
conditions, including cancer,
arthritis and lung disease.
Laboratory experiments have
demonstrated that Vitamin
C neutralizes these harmful
oxidants derived from phagocytes(7).
Vitamin C after being converted
to dehydroascorbic acid
by free radical reactions,
is regenerated via the glutathione
enzyme complex(161). It
is interesting that the
Vitamin C (ascorbate) free
radical itself, rather than
initiating radical chain
reactions, does not react
with oxygen and quenches
itself very rapidly. And
since Vitamin C reacts directly
with hydrogen peroxide,
it acts as a protectant
against damage from lipid
peroxides.
However,
an even more fascinating
chapter in the Vitamin C
– free radical protection
story is the finding that
Vitamin C and Vitamin E
work together, synergistically,
in inhibiting the free radical
chain oxidation of lipids(161).
Vitamin C actually regenerates
the Vitamin E radical, enabling
these two potent anti-oxidants
to cooperate in what is
called "redox coupling".
Vitamin E does its work
within the membrane, while
Vitamin C participates from
the aqueous cellular compartment.
It had
been noted previously that
Vitamin C "spared"
the consumption of Vitamin
E in free radical chain
oxidation experiments; however,
it had never been shown
whether Vitamin C, located
in the aqueous part of the
cell and Vitamin E, situated
within the lipid membrane,
could actually cooperate
to prevent these detrimental
lipid peroxidation events.
Results reported on at the
latest Vitamin C Conference
showed that, in fact, even
though Vitamin C is sequestered
in the aqueous part of the
cell and cannot penetrate
the lipid membrane, that
Vitamin C is accessible
to the Vitamin E radical
and does regenerate Vitamin
E(161). Since Ester-CR ascorbate
is fat soluble, its Vitamin
E regeneration activity
may be superior to that
of Vitamin C.
Multiple sources of free
radicals abound –
chemicals in our food, heating
unsaturated oils, margarines
and other unsaturated fats(74-5),
not to speak of the toxic
chemicals ingested from
pesticides, nitrites, etc.
etc. In the face of this
growing menace from so many
seeminagly unavoidable threats
to our health, there would
appear to be two typical
"knee-jerk" reactions
for the individual: 1) To
scrupulously avoid contact
with every conceivable toxic
substance, environment,
food and stress, since stress
plays a major role in releasing
free radicals; or 2) To
throw up one's hands in
despair and do nothing,
deciding that it's just
not possible to eliminate
toxins from life in the
twentieth century. The first
response, taken to extremes,
could lead to an acutely
neurotic and/or hermetic
lifestyle (taking to the
clean air of the Himalayas
to meditate alone for the
rest of one's life); the
second, likewise could provide
an excuse or rationalization
for laziness in controlling
one's daily living habits.
What then,
is a sensible response to
this ever-mounting barrage
to our health from so many
sources? Is there something
we can do in the face of
so many health threats around
every corner? It would certainly
appear to make eminent sense
to inform ourselves thoroughly
and accurately about health
risk factors such as free
radicals and toxic oxygen
species without going overboard
in panic (we have survived
this long, after all), and
to implement as many health
promoting measures in our
lives as feels appropriate
and convenient. Obviously
there are degrees of urgency,
depending upon our current
state of health; someone
seriously ill from cancer
or arthritis is much more
vulnerable to toxic overload
than, say an Olympic decathalon
athlete. Interestingly,
however, it could be said
that the average Olympic
athlete is much more aware
and careful about his/her
health and environment than
the rest of the population.
And that could be the most
eloquent testimony of all
to taking responsibility
for every aspect of our
lifestyle.
The generous
provision of natural anti-oxidants
including Vitamin C in one's
daily dietary regime would
appear to make more than
adequate sense in promoting
better defense against those
all-pervasive destructive
free radical elements emanating
from within and without
our bodies.
