An antioxidant is a chemical that prevents the oxidation of other chemicals. In
biological systems, the normal processes of oxidation (plus a minor contribution from
ionizing radiation) produce highly reactive free radicals. These can readily react
with and damage other molecules: in some cases the body uses this to fight infection.
In other cases, the damage may be to the body's own cells. The presence of extremely
easily oxidisable compounds in the system can "mop up" free radicals before they
damage other essential molecules.
The following vitamins have shown positive antioxidant effects:
Retinol.
(Vitamin A or beta-carotene) has been discovered to protect dark green, yellow and
orange vegetables and fruits from solar radiation damage, and is thought to play a
similar role in human body. Carrots, squash, broccoli, sweet potatoes, tomatoes,
kale, collards, cantaloupe, peaches and apricots are particularly rich sources of
beta-carotene.
Ascorbic acid (Vitamin C) is a water-soluble compound that fulfills this role, among
others, in living systems. Important sources include citrus fruits (like oranges,
sweet lime, etc.), green peppers, broccoli, green leafy vegetables, strawberries, raw
cabbage and tomatoes.
Vitamin E
(tocopherol) is fat soluble and protects lipids. Sources include wheat germ, nuts,
seeds, whole grains, green leafy vegetables, vegetable oil and fish-liver oil.
Selenium is
best obtained through foods, as large doses of the supplement form can be toxic. Good
food sources include fish, shellfish, red meat, grains, eggs, chicken and garlic.
Vegetables can also be a good source if grown in selenium-rich soils.
Several food additives (including ascorbic acid and tocopherol-derived compounds) are
used as antioxidants to help guard against deterioration of food.
Other antioxidants are enzymes. These include glutathione peroxidase, superoxide
dismutase and catalase.
A lot of damage is done by free radicals in mitochondria (damage to mitochondrial
DNA, which is very much exposed to free radicals because of where its location
between the inner and outer mitochondrial membranes; and the enzymes that copy it
don't do error-checking/correction, as the ones that copy the nuclear DNA do). Most
antioxidants, however (including vitamin C and
vitamin E) can't get into mitochondria for various reasons (e.g. because it's
charged). But a group of scientists in Russia (led by V. Skulachev) has created a
custom antioxidant ("Skulachev ion" is forming the point of the molecule and
penetrates the mitochondrial membrane and the "antioxidising" part is attached behind
it) that can enter the mitochondria and stays there preventing damage to DNA.
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