Vitamin C
Main Characteristics
• It is known for its most common
deficiency, scurvy.
• It is known by the following
names: ascorbic acid, dehydroascorbic acid or anti-scurvy vitamin.
• Both forms are metabolically
active in the body: ascorbate and dehydroascorbic acid.
• It is water-soluble, that is,
soluble in aqueous media.
• It is absorbed in the small
intestine and acts in the bloodstream, reaching higher concentrations in the
adrenal cortex, pituitary gland and pancreas.
• Vitamin C is not stored in the
body, so it needs to be consumed periodically and if consumed in excess it is
quickly excreted in the urine.
Main Functions and Mechanisms of
Action
• Antioxidant action in the body:
it acts in the elimination of free radicals or in the preservation of processed
foods.
• It acts as a cofactor or
co-substrate for the synthesis of several enzymes.
• Acts in the biosynthesis of
collagen, essential for healing processes: by hydroxylating proline and lysine.
• Acts in the biosynthesis of
carnitine, used for the synthesis of ATP.
• Action on oral health:
preventing the increase in the permeability of the gingival sulcus,
facilitating the entry of harmful substances and causing an inflammatory
process.
• Acts on blood vessels: it is
necessary for the formation of glycosaminoglycans that act as constituents of
the vessel wall.
• Action in the prevention of
chronic non-communicable diseases: action in the conversion of cholesterol into
bile acids.
• Participates in the immune
system: increases levels of IgA, IgM, complement C3 fraction and interferon,
stimulating phagocytosis.
Bioavailability
• Vitamin C absorption occurs
through an active sodium-dependent process in the brush border membrane in the
intestinal mucosa, but it can also be absorbed by the oral mucosa mediated by
carriers.
• Vitamin C absorption is around
80 to 90% of the total intake from food sources, so if more than the
recommended amount is consumed, the excess unabsorbed serves as a substrate for
intestinal bacteria.
Possible interactions
• It is important to mention that
vitamin C may interact with some drugs such as tetracycline antibiotics, oral
contraceptives, aspirin, among others, in which cases there may be depletion of
the vitamin.
Interaction between Nutrients
• With high intake of vitamin C,
there may be depletion of copper, due to decreased intestinal absorption and
excessive absorption of iron.
Scientific evidence regarding the
effectiveness of supplementation
• When comparing the two forms of
vitamin C administration, it is important to emphasize that there is no
difference between the synthetic and natural forms in terms of bioavailability.
• The antioxidant capacity of
vitamin C is the result of its high reducing power, capable of providing
hydrogen ions and electrons, either by acting directly on reactive oxygen
species or by regenerating other antioxidant compounds present in the cell, such
as vitamin E and GSH. There is evidence that intracellular vitamin C can donate
electrons to a membrane oxidoreductase enzyme, revealing that its antioxidant
potential can also protect the plasma membrane.
• During the liver detoxification
process, toxins are metabolized, generating free radicals that need to be
neutralized by antioxidants. In the case of vitamin C deficiency, contamination
by heavy metals and drugs may occur.
• Some studies show that vitamin
C supplementation can help improve the functions of the immune system in
natural killer cells, antimicrobials, increased lymphocyte proliferation and
hypersensitivity activity. Thus, in vitamin C deficiency, there is low immune
resistance.
• Studies on cancer prevention
have shown that vitamin C supplementation contributed to improvements in the
terminal phase of the disease, due to the action of dehydroascorbic acid with
homocysteine, which produces a toxic substance capable of promoting the death
of cancer cells.
• Vitamin C supplementation in
patients with anemia has shown positive results, because in vitamin C
deficiency, iron bioavailability, absorption and storage decrease, causing the
depletion of iron stores by ferritin. But it is also important to highlight
that vitamin C associated with vitamin E, folic acid, copper and zinc,
increased the bioavailability of iron, highlighting the importance of
associated vitamin supplementation.
• In cardiovascular diseases, its
main effect in supplementation is linked to the combination of vitamin C and
vitamin E due to the antioxidant activity of both, thus preventing the
formation of oxidized LDL and neutralizing its harmful effects on blood vessels;
the maintenance of nitric oxide, which is responsible for stimulating vascular
relaxation, allowing good blood flow (vitamin C protects the synthesis of NO);
in the synthesis of collagen, since vitamin C deficiency impairs collagen
production, increasing the risk of atherosclerotic plaque formation in blood
vessels.
• Vitamin C is essential for bone
formation, as it stimulates collagen synthesis, which is why studies have found
that supplementation of 100mg to 500mg/day can help prevent reduced bone
density, maintain osteoblast function and improve calcium bioavailability,
preventing fractures and osteoporosis, especially in menopausal women who are
taking hormone replacement therapy.
• Vitamin C supplementation is
essential for smokers, as these individuals are contaminated with heavy metals
(Cadmium), have increased oxidative stress, and consequently use their immune
system more to inactivate inflammatory processes and NF-kappaB.
Risks of overdose
• Evidence of vitamin C toxicity
has not yet been described, but doses greater than 3g/day may cause
gastrointestinal discomfort, osmotic diarrhea, oxalate excretion, and kidney
stone formation (in predisposed individuals), or doses of 500mg/day may interfere
with the absorption of vitamin B1. Therefore, people with a history of gout,
kidney stones, or kidney disease should not take more than 1g/day under
supervision. In addition, it may have pro-inflammatory effects.
Genetic factors
The GSTT1 gene is an enzyme that
plays an important role in the utilization of vitamin C. There may also be a
deletion of this gene, which may result in a decreased ability to process
vitamin C and this means a greater need for vitamin C.
Food sources
FOOD AMOUNT OF VITAMIN C IN 100g
Acerola 941.4 mg
Pepper (yellow, green and red)
Between 100 to 200 mg
Papaya 82.2 mg
Red guava 80.6 mg
Formosa papaya 78.5 mg
Sautéed butter cabbage 76.9 mg
Kiwi 70.8 mg
Palmer mango 65.5 mg
Strawberry 63.6 mg
Pear orange 53.7 mg
Poncã tangerine 48.8 mg
Broccoli 42 mg
Tahiti Lime 38.2 mg
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