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Vitamin C, also known as L-ascorbic acid or L-ascorbate, is a water soluble vitamin, meaning it is not stored in the body in large amounts. The name "ascorbic" comes from its property of preventing and curing scurvy, a vitamin C deficiency. As water soluble vitamins enter the body, they are put to work immediately and any excess is eliminated from the body via the urine. Because the body is not able to store these vitamins, they must be constantly resupplied. (Hickey, S. Roberts, H. 2005) Vitamin C is so critical to living creatures that almost all mammals can use their own cells to make it. Most mammals make ascorbic acid in their liver where the enzyme L-gulonolactone oxidase is required to convert glucose to ascorbic acid. (Harris, JR 2007) Humans, gorillas, chimps, bats, guinea pigs and birds are some of the few animals that cannot make vitamin C inside of their own bodies. Because these animals cannot produce vitamin C, it must be obtained from a food source or supplement. Humans vary greatly in their vitamin C requirement. It's natural for one person to need 10 times as much vitamin C as another person. A person's age and health status can dramatically change his or her need for vitamin C.
Source: Vitamin C is produced naturally in fruits and vegetables. Terminalia ferdinandiana or The Kakadu Plum has the highest known vitamin C concentration than any other food source at 3200-5000mg/100g, compared with 50mg/100g for oranges. Other common sources of vitamin C are blackcurrant, red peppers, parsley, strawberries and kiwi fruit. Vitamin C is sensitive to the light, air and heat. (Mason, JB. 2007) The most vitamin C can be obtained if fruits and vegetables are eaten raw or cooked lightly. About 25% of the vitamin C in vegetables can be lost simply by blanching. This same degree of loss occurs in the freezing and unthawing of vegetables and fruits. Cooking of vegetables and fruits for longer periods of time can result in a loss of over 50% the total vitamin C content. In animals Vitamin C is found mostly in the liver and least in the muscle tissue. Since most of the meat consumed in the human diet is animal muscle, it is an unreliable source. (Hartigan, K. 2008)
Chemical Properties: Ascorbic acid is a naturally occurring compound. The IUPAC name for Ascorbic Acid is 2-oxo-L-threo-hexono-1,4- lactone-2,3-enediol. It has the molecular formula of C6H8O6 and appears as a white or light yellow solid. (Levine, M. 2001) As mentioned before vitamin C is very sensitive to even slight heating, to the light, and to the action of oxidizing agents and metal ions. Vitamin C is readily oxidized, especially in aqueous solutions, by reacting with atmospheric oxygen and behaves as a two-electron donor. (Harris, JR 2007) Ascorbic acid is active in many biological processes; it maintains prolyl hydroxylase in an active form by preserving its iron atom in the reduced Fe2+ state and it keeps collagen in a sufficiently hydroxylated form preventing skin lesions and blood-vessel fragility that are so prominent in scurvy.
Physiological Properties: Ascorbic Acid is a sugar acid with antioxidant properties. It helps to maintain healthy collagen in the skin, repair damaged tissue, promote healthy teeth and bones, and boost the immune system. Ascorbate acts as a reducing agent to reverse oxidation in aqueous solution. When there are more free radicals (reactive oxygen species) in the human body than antioxidants, the condition is called oxidative stress. Oxidative stress induced diseases encompass cardiovascular diseases, hypertension, chronic inflammatory diseases and diabetes. (Carr, AC. Frei, B. 1999) Absorption of vitamin C is greater when several individual doses of vitamin C, in quantities less than one gram, are taken throughout the day rather than one large dose. A high iron concentration in the gastrointestinal tract may cause oxidative destruction and in turn impair uptake. Active transport is the main mechanism of vitamin C distribution within the body. Simple diffusion may occur in the mouth and stomach but accounts for only a very small percentage of uptake. In the plasma absorbed ascorbic and dehydroascorbate (DHAA) can either be transported freely or be bound to albumin. Ascorbate can also move into body cells and tissues. (Mason, JB. 2007) Vitamin C also aids the metabolism of tyrosine, folic acid, and tryptophan. Tryptophan is converted in the presence of ascorbic acid to 5-hydroxytryptophan, which forms serotonin, an important brain chemical. (Hartigan, K. 2008)
Vitamin C is stored throughout body tissues and blood. Ascorbic acid content of blood components, fluid and tissue varies widely on an individual basis. Tissue concentrations exceed those found in the plasma by three to ten times. Tissues that store average levels of vitamin C include the kidneys, brain, liver, lungs, and thyroid. The water-soluble properties of vitamin C prevent it from being stored in the adipose tissue of the body. (Carr, AC. Frei, B. 1999)
Metabolic Role: Metabolites of vitamin C include dehydroascorbate (DHAA), oxalic acid, 2-O-methyl ascorbate and 2-ketoascorbitol. (Englard, S. Seifter, S. 1986) Dehydroascorbate is an oxidized form of ascorbic acid. Vitamin C does not pass from the blood stream into the brain. Even though the brain is one of the organs which contain the greatest concentration of vitamin C. Instead it is dehydroascorbate that is transported through the blood-brain barrier via GLUT1 transporters, and then converted to vitamin C. Oxalic acid is commonly found within the plant kingdom. 2-0-methyl Ascorbate is a salt produced from ascorbic acid. (Hartigan, K. 2008)
Deficiency and Disease: Symptoms of a vitamin C deficiency include weak immune function, including susceptibility to colds and other infections. The lining of the respiratory tract also depend heavily on vitamin C for protection, respiratory infection and other lung-related conditions can also be symptomatic of vitamin C deficiency. (Groff, JL. Et. Al. 2002) Scurvy is a disease resulting from the deficiency of vitamin C. Scurvy is characterized by swollen and bleeding gums with loosened teeth, soreness and stiffness of the joints and lower extremities, bleeding under the skin and in deep tissues, slow wound healing, and anemia. More severe symptoms include psychotic disorders, black and blue spots and broken capillaries. These occur shortly before death. Scurvy is one of the accompanying diseases of malnutrition and thus is still widespread in areas of the world depending on external food aid. Though rare, there are also documented cases of scurvy due to poor dietary choices by people living in industrialized nations. (Downing, C. Et al. 2006)
Toxicity: At high supplemental doses involving 5g or more of vitamin C a day, diarrhea can result from the fluid in the intestine becoming too concentrated. Vitamin C can be transformed in the body to oxalate, oxalic acidââ‚¬â„¢s conjugate base, which is a common constituent of kidney stones. People who are prone to kidney stones may want to avoid large doses of the vitamin. People who lack the control to regulate iron uptake, such as sufferers of Haemochromatosis, should also avoid large doses of the vitamin as it increases iron absorption. Haemochromatosis is defined as an iron overload with a hereditary/primary cause or originating from a metabolic disorder.
Functions: Vitamin C serves a primarily protective role in the body. Cardiovascular diseases, some cancers, joint diseases and cataracts are associated with vitamin C deficiency. These could be partly prevented by an optimal intake of vitamin C. Vitamin C achieves much of its protective effect by functioning as an antioxidant and preventing oxygen based damage to cells in the body. Structures that contain fat (e.g. lipoprotein molecules which enable fats to be carried in the blood stream) are particularly dependent on vitamin C for protection. For iron-deficiency anemia, vitamin C helps the absorption of iron from the gastrointestinal tract. (Simon, H. Zieve, D. 2009)
Bioavailability: Natural and synthetic ascorbic acid are chemically identical. There appears to be no clinically significant difference in the bioavailability and bioactivity of natural ascorbic acid and synthetic ascorbic acid. The average half-life of ascorbic acid is believed to be between 16 and 20 days. Its half-life is inversely related to intake. (Englard, S. Seifter, S. 1986) The water-soluble properties of vitamin C lead to urinary excretion of the vitamin. The kidneys play a major role in vitamin C excretion and retention. Levels within the body that are 1500 mg or less will result in no urinary excretion of vitamin C. Drugs which can deplete the bodyââ‚¬â„¢s supply of ascorbic acid include contraceptives like the pill, anti-inflammatory drugs such as aspirin, antibiotics and cancer treatment drugs.
Fortification: Ascorbic acid is used widely in the food industry for its nutritional value and for the many functional contributions it has to product quality. Because ascorbic acid is an antioxidant, it helps to improve the colour and palatability of many food products. There are technologies available for vitamin C fortification of fruit juices, fruit juice drinks, other related beverages, dairy products and some breakfast cereals. Some juices that are not normally a source of vitamin C can have vitamin C added. Although vitamins in their purest form have little taste, it is important that the addition of the vitamin to the product does not change its taste. This could affect the sale of the product. During the manufacturing of fruit juices from fruits such as apples and peaches, ascorbic acid may be added during the crushing, straining or pressing processes. This helps to prevent the enzymatic browning of the raw fruits. Browning of fruits occurs when the polyphenolases, which are found in the tissue of fruits, catalyze the oxidation of phenols, also naturally present in the fruit, to form quinones. The quinones can then polymerize to create melanins. Melanins are the compounds which cause the brown pigmentation. (Vitamin C Foundation, 2009)
Supplements: Dietary supplements typically contain vitamin C in the form of ascorbic acid. Because vitamin C is better absorbed in the presence of flavonoids, many supplement manufacturers also add flavonoids to their products. Buffered versions of vitamin C are also commonly available. These buffered forms usually combine vitamin C with minerals like calcium, magnesium or potassium. Buffered vitamin C may be helpful for individuals who have stomach sensitivity or who are taking higher doses of the supplement. Also widely available is a complex form of vitamin C in which ascorbic acid is combined with several of its naturally occurring metabolites including dehydroascorbate, threonate and aldonic acids. (Hamrick, I. Counts, SH. 2008)
Conclusion: In conclusion vitamin C is a water-soluble vitamin that is necessary for normal growth and development. There are many medical benefits of having a regular vitamin C intake. The body does not manufacture vitamin C on its own, nor does it store it. It is therefore important to include plenty of vitamin C-containing foods in a daily diet.
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