c good vitamin
Ascorbic acid bears numerous physiological functions in human body. The functions include the synthesis of collagen, carnitine and neurotransmitter, the synthesis and catabolism of tyrosine and the metabolism of microsome. The main action of ascorbate in most of the synthesis above is functioning as a reducing agent to maintain iron and copper atoms in their reduced state.
- Three participate in collagen hydroxylation. These reactions add hydroxyl groups to the amino acids proline or lysine in the collagen molecule via prolyl hydroxylase and lysyl hydroxylase, both requiring vitamin C as a cofactor. Hydroxylation allows the collagen molecule to assume its triple helix structure and making vitamin C essential to the development and maintenance of scar tissue, blood vessels, and cartilage.
- 2 are necessary for synthesis of carnitine. Carnitine is essential for the transport of fatty acids into mitochondria for ATP generation.
- The remaining three have the following functions in common but do not always do this:
- dopamine beta hydroxylase participates in the biosynthesis of norepinephrine from dopamine.
- another enzyme adds amide groups to peptide hormones, greatly increasing their stability.
- one modulates tyrosine metabolism.
Antioxidant
Ascorbic acid is well known for its antioxidant activity. Ascorbate acts as reducing agent to reverse oxidation in aqueous solution. When there are more free radicals (Reactive oxygen species) in the body versus antioxidant, human is under the condition called Oxidative stress. Oxidative stress induced diseases encompass cardiovascular diseases, hypertension, chronic inflammatory diseases and diabetes The plasma Ascorbate concentration in oxidative stress patient (less than 45umol/L) measured is lower than healthy individual (61.4-80umol/L) . According to McGregor and Biesalski (2006) increasing plasma ascorbate level may have therapeutic effects in oxidative stress individual. Individual with oxidative stress and healthy individual have different pharmacokinetics of ascorbate.
Pro-oxidant
Ascorbic acid behaves not only as antioxidant but also as pro-oxidant . Ascorbic acid reduced transition metals, such as Cupric ions (Cu2+) to cuprous (Cu1+) and Ferric ions (Fe3+) to ferrous (Fe2+) during conversion from ascorbate to dehydroxyascorbate In Vitro . This reaction can generate superoxide and other ROS. However, in the body, free transition elements are unlikely to be present while iron and copper is bound to diverse proteins . Recent studies show that intravenous injection of 7.5g of ascorbate daily for 6 days did not increase pro-oxidant markers ; thus, ascorbate as a pro-oxidant is unlikely to convert metals to create ROS in vivo.
Daily requirements
The North American Dietary Reference Intake recommends 90 milligrams per day and no more than 2 grams per day (2000 milligrams per day). Other related species sharing the same inability to produce vitamin C and requiring exogenous vitamin C consume 20 to 80 times this reference intake. There is continuing debate within the scientific community over the best dose schedule (the amount and frequency of intake) of vitamin C for maintaining optimal health in humans. It is generally agreed that a balanced diet without supplementation contains enough vitamin C to prevent scurvy in an average healthy adult, while those who are pregnant, smoke tobacco, or are under stress require slightly more.
High doses (thousands of milligrams) may result in diarrhea in healthy adults. Proponents of alternative medicine (specifically orthomolecular medicine) claim the onset of diarrhea to be an indication of where the body’s true vitamin C requirement lies, though this has yet to be clinically verified.
Food preparation
Vitamin C chemically decomposes under certain conditions, many of which may occur during the cooking of food. Normally, boiling water at 100°C is not hot enough to cause any significant destruction of the nutrient, which only decomposes at 190°C, despite popular opinion. However, pressure cooking, roasting, frying and grilling food is more likely to reach the decomposition temperature of vitamin C. Longer cooking times also add to this effect, as will copper food vessels, which catalyse the decomposition.
Another cause of vitamin C being lost from food is leaching, where the water-soluble vitamin dissolves into the cooking water, which is later poured away and not consumed. However, vitamin C doesn't leach in all vegetables at the same rate; research shows broccoli seems to retain more than any other. Research has also shown that fresh-cut fruits don't lose significant nutrients when stored in the refrigerator for a few days.
Vitamin C supplements
Vitamin C is the most widely taken dietary supplement. It is available in many forms including caplets, tablets, capsules, drink mix packets, in multi-vitamin formulations, in multiple antioxidant formulations, and crystalline powder. Timed release versions are available, as are formulations containing bioflavonoids such as quercetin, hesperidin and rutin. Tablet and capsule sizes range from 25 mg to 1500 mg. Vitamin C (as ascorbic acid) crystals are typically available in bottles containing 300 g to 1 kg of powder (a teaspoon of vitamin C crystals equals 5,000 mg).
Artificial modes of synthesis
Vitamin C is produced from glucose by two main routes. The Reichstein process, developed in the 1930s, uses a single pre-fermentation followed by a purely chemical route. The modern two-step fermentation process, originally developed in China in the 1960s, uses additional fermentation to replace part of the later chemical stages. Both processes yield approximately 60% vitamin C from the glucose feed.
Research is underway at the Scottish Crop Research Institute in the interest of creating a strain of yeast that can synthesise vitamin C in a single fermentation step from galactose, a technology expected to reduce manufacturing costs considerably.
World production of synthesised vitamin C is currently estimated at approximately 110,000 tonnes annually. Main producers have been BASF/Takeda, DSM, Merck and the China Pharmaceutical Group Ltd. of the People's Republic of China. China is slowly becoming the major world supplier as its prices undercut those of the US and European manufacturers. By 2008 only the DSM plant in Scotland remained operational outside the strong price competition from China. The world price of vitamin C rose sharply in 2008 partly as a result of rises in basic food prices but also in anticipation of a stoppage of the two Chinese plants, situated at Shijiazhuang near Beijing, as part of a general shutdown of polluting industry in China over the period of the Olympic games.
Fortification
In Addition of Vitamins and Minerals to Food, 2005: Health Canada's Proposed Policy and Implementation Plans . Ascorbate is categorized in ‘Risk Category A nutrients’ which for ‘‘those nutrients for which a UL was set but with a wide margin of safe intake; and those nutrients with a narrow margin of safety, but non-serious critical adverse effects’’. The level of additions set by health canada are Minimum of 3 mg or 5 % of RDI to be able to claim as "Source" and maximum fortification of 12 mg (20 % of RDI) to be claimed "Excellent Source".
References
- ^ McCluskey, Elwood S. (1985). "Which Vertebrates Make Vitamin C?" (PDF). Origins 12 (2): 96–100. http://www.grisda.org/origins/12096.pdf.
- ^ a b "Vitamin C". Food Standards Agency (UK). http://www.eatwell.gov.uk/healthydiet/nutritionessentials/vitaminsandminerals/vitaminc/. Retrieved on 2007-02-19.
- ^ "Vitamin C". University of Maryland Medical Center. January 2007. http://www.umm.edu/ency/article//002404.htm. Retrieved on 2008-03-31.
- ^ a b Higdon, Jane, Ph.D. (2006-01-31). "Vitamin C". Oregon State University, Micronutrient Information Center. http://lpi.oregonstate.edu/infocenter/vitamins/vitaminC/. Ret
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