General Description
Vitamin C is a water-soluble antioxidant required by every tissue
in the body. First isolated in 1928 by Albert Szent-Gyorgi, vitamin
C is involved in hundreds of vital biochemical reactions and is
the body's most important antioxidant, serving as the first line
of defense against free-radical induced damage. While most animals
manufacture their own vitamin C, in humans this is not the case;
it must be included in the diet. Because it is a water-soluble vitamin
and is not stored in the body, it is essential that people consume
vitamin C daily. Supplemental vitamin C is sold in many forms, including
powders, timed-release tablets, capsules, etc. Non-acidic, "buffered"
forms, in which ascorbic acid is bonded to a mineral (i.e. calcium,
potassium, sodium, and magnesium ascorbates) are available for those
who experience gastric discomfort with regular vitamin C supplements.
Food sources
Good food sources of vitamin C include citrus fruits, broccoli,
peppers, tomatoes, and dark-green, leafy vegetables like spinach
and kale.
Health applications
Functions and uses
The primary function of vitamin C is in the manufacture of collagen,
which is the main protein substance in human tissues. This makes
vitamin C important for virtually all body systems. Vitamin C is
essential for healthy skin, gums, blood vessels, eyes, central nervous
system and reproductive function. It is also required for the production
of enzymes that help rid the body of toxins, including lead and
other environmental pollutants. Severe vitamin C deficiency causes
scurvy, one of the most prevalant deficiency diseases throughout
history. The classic symptoms of scurvy include bleeding gums, extensive
bruising, poor wound healing, and increased susceptibility to infection.
Before the development of modern food preservation techniques, scurvy
would reach epidemic proportions during winter months in areas where
fresh fruits and vegetables were not available. Scurvy was common
on long ocean voyages until late in the 18th century when it was
discovered that rationing citrus fruits could prevent the disease.
Cardiovascular
health
Much of the research on vitamin C has focused on its role in cardiovascular
health. As an antioxidant, vitamin C helps protect LDL (the "bad
cholesterol") from oxidation.1 Oxidized LDL
is a major contributor to atherosclerosis, which can lead to heart
attack or stroke. Analysis of data from 6,624 men and women showed
that vitamin C levels were independantly associated with the prevalence
of cardiovascular disease, and that increasing serum vitamin C
levels could reduce the risk of coronary heart disease or stroke
by as much as 11percent.2
Immune function
The role of vitamin C in immune system function has been the subject
of much debate since Dr. Linus Pauling's Vitamin C and the Common
Cold was published in 1970, and the practice of supplementing
extra vitamin C during a cold remains widely popular. Studies
conducted on cold sufferers have shown that vitamin C supplements
can significantly reduce the duration of cold symptoms.3-5
Because it performs vital functions in the production and activity
of white blood cells, it has been suggested that vitamin C may
play a role in cancer prevention. In vitro and in vivo studies
have shown that vitamins C and E can inhibit the formation of
cancer-causing compounds called nitrosamines. Other in vitro studies
have shown vitamins C and E to inhibit genetic mutation and tumor
cell growth.6 While many studies on its role
in cancer prevention are inconclusive, there is evidence that
vitamin C may help protect against cancers of the colon,7,8
the upper digestive tract, and cervix.9 Although
no role for vitamin C in cancer treatment has been established,
some cancer treatments deplete vitamin C levels in the body,10
and increased intake may be advisable in such cases.
Dosage/toxicity
The RDA for vitamin C is 60 mg per day, but this is widely believed
to be too low. Many nutritionists recommend 250 to 500 mg per
day for healthy people, but doses of up to 5,000 mg per day have
been recommended in conditions of increased oxidative stress.
Factors that increase vitamin C requirements include smoking,
diabetes, high-fat diets, physical wounds, infections, and many
illnesses. Vitamin C is absorbed more efficiently when consumed
with bioflavonoids, and they may also enhance its antioxidant
potency. Because vitamin C is not stored in the body, it is best
to consume it in divided doses throughout the day, preferably
with meals. Vitamin C has no known toxicity, even at extremely
high doses. Adverse effects including stomach upset, intestinal
gas and diarrhea have been reported with high-dose supplementation,
but these symptoms normally reverse with reduction of intake.
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