Vitamin C - Vitamin Basics
Vitamin C can enhance the immune system, reduce the risk of heart disease and stroke, gums and teeth will help prevent cataracts, accelerated wound healing, relieve asthma, infertility treatment has some effect. Intake - per person per day of vitamin C intake of 30 mg or so like, even men should be noted that smoking increases the amount of supplement, but do not add more than 35 mg. Food sources - an adequate supply of vitamin C can delay aging. Kiwi, oranges, lemons, grapefruit are good sources of vitamin C.
38 Vitamin C Synonyms Ascorbic acid, hexuronic acid, anti-scorbutic vitamin Chemistry L-ascorbic acid (2,3-endiol-L-gulonic acid- -lactone), dehydro-L-ascorbic acid (2-oxo-L-gulonic acid- -lactone). Vitamin C crystals in polarised light CH2OH H OH O O H OH OH Molecular formula of vitamin C 39 Introduction for blood cholesterol levels and gall- bage, spinach and tomatoes is also stones. In addition, vitamin C plays of importance. Depending on the an important role in the synthesis of season, one medium-sized glass of Vitamin C is water-soluble, and several important peptide hormones freshly pressed orange juice (i.e. 100 probably the most famous of all the and neurotransmitters and carnitine. g) yields from 15 to 35 mg vitamin C. vitamins. Even before its discovery Finally, vitamin C is also a crucial in 1932, physicians recognised that factor in the eye's ability to deal with there must be a compound in citrus oxidative stress, and can delay the fruits preventing scurvy, a disease progression of advanced age-related Absorption and that killed as many as 2 million macular degeneration (AMD) and sailors between 1500 and 1800. vision-loss in combination with other body stores Later researchers discovered that antioxidant vitamins and zinc. man, other primates and the guinea Intestinal absorption of vitamin C pig depend on external sources to depends on the amount of dietary cover their vitamin C requirements. Main functions in a nutshell: intake, decreasing with increasing Most other animals are able to syn- • Immune stimulation intake levels. At an intake of 30 to thesise vitamin C from glucose and • Anti-allergic 180 milligrams, about 70% to 90% is galactose in their body. • Antioxidant absorbed; about 50% of a single • “Cement” for connective tissues dose of 1 to 1.5 grams is absorbed; • Wound healing and only 16% of a single dose of 12 • Teeth and gum health grams is absorbed. Up to about 500 Functions • Aids iron absorption milligrams are absorbed via a sodi- • Eye health um-dependent active transport The most prominent role of vitamin C process, while at higher doses sim- is its immune stimulating effect, ple diffusion occurs. which is important for the defence against infections such as common The storage capacity of water-solu- colds. It also acts as an inhibitor of Dietary sources ble vitamins is generally low com- histamine, a compound that is pared to that of fat-soluble ones. released during allergic reactions. As Vitamin C is widely distributed in Humans have an average tissue a powerful antioxidant it can neu- fruits and vegetables. Citrus fruits, store of vitamin C of 20 mg/kg body tralise harmful free radicals and aids blackcurrants, peppers, green veg- weight. The highest concentration is in neutralising pollutants and toxins. etables (e.g. broccoli, Brussels found in the pituitary gland (400 Thus it is able to prevent the forma- sprouts), and fruits like strawberries, mg/kg); other tissues of high con- tion of potentially carcinogenic guava, mango and kiwi are particu- centration are the adrenal glands, nitrosamines in the stomach (due to larly rich sources. On a quantity liver, brain and white blood cells consumption of nitrite-containing basis, the intake of potatoes, cab- (leukocytes). foods, such as smoked meat). Importantly, vitamin C is also able to regenerate other antioxidants such as vitamin E. Vitamin C is required Vitamin C content of foods Measurement for the synthesis of collagen, the intercellular “cement” substance Food Vitamin C Vitamin C can be measured in the which gives structure to muscles, (mg/100g) blood plasma and other body tis- vascular tissues, bones, tendons sues by various techniques. Also Acerolas 1600 and ligaments. Due to these func- dipstick tests for estimation of vita- tions vitamin C, especially in combi- Blackcurrants 200 min C levels in the urine are avail- nation with zinc, is important for the Peppers 138 able. Less satisfying, however, is the healing of wounds. Vitamin C con- Broccoli 115 evaluation of the analytical data con- tributes to the health of teeth and Fennel 95 cerning the true reflection of the gums, preventing haemorrhaging Kiwis 71 body status. Threshold values are and bleeding. It also improves the difficult to define and the subject of Strawberries 64 absorption of iron from the diet, and controversial discussion. Typical Oranges 49 is needed for the metabolism of bile blood plasma levels are in the range acids, which may have implications (Souci, Fachmann, Kraut) of 20 to 100 µmol/L. 40 Stability sants, diuretics, birth control pills characterised by weakening of col- and aspirin, deplete the tissues of lagenous structures, resulting in Vitamin C is sensitive to heat, light vitamin C. This is also true of certain widespread capillary bleeding. and oxygen. In food it can be partly habits, for example alcohol con- Infantile scurvy causes bone malfor- or completely destroyed by long sumption. mations. Bleeding gums and loosen- storage or overcooking. Refrige- ing of the teeth are usually the earli- ration can substantially diminish est signs of clinical deficiency. vitamin C loss in food. Haemorrhages under the skin cause extreme tenderness of extremities and pain during movement. If left Influence of storage and preparation on vitamin C loss in foods untreated, gangrene and death may ensue. Nowadays this is rare in Food Storage/Preparation Vitamin C Loss developed countries and can be pre- Potatoes 1 month 50% vented by a daily intake of about 10- Fruit 1 month 20% 15 mg of vitamin C. However, for optimal physiological functioning Apples 6-9 months 100% much higher amounts are required. Milk UHT 25% Fruit Sterilisation 50% Fruit Air drying 50-70% The development of vitamin C Leafy vegetables Canning 48% deficiency can be caused by: • Inadequate storage and prepa- ration of food • Gastrointestinal disturbances Modified from Oberbeil, Fit durch • Stress and exercise Vitamine, Die neuen Wunderwaffen, Deficiency • Infections Südwest Verlag GmbH & Co. KG, • Smoking München 1993 Early symptoms of vitamin C defi- • Diabetes ciency are very general and could • Pregnancy and lactation also indicate other diseases. They include fatigue, lassitude, loss of Interactions appetite, drowsiness and insomnia, feeling run-down, irritability, low Positive interactions resistance to infections and petechi- The presence of other antioxidants, ae (minor capillary bleeding). Severe such as vitamin E and beta- vitamin C deficiency leads to scurvy, carotene, supports the protective antioxidant action of vitamin C. Other vitamins, such as those of the B-complex (particularly B 6 , B 12 , folic acid and pantothenic acid) and some pharmacologically active sub- stances, as well as the naturally occurring compounds known as bioflavonoids, may have a spar- ing effect on vitamin C. Negative interactions Due to toxic compounds in smoke, the vitamin C require- ment for smokers is about 35 mg/day higher than for non- smokers. Also several pharma- cologically active compounds, among them some anti-depres- 41 Disease plaque, as this helps to prevent the ment in severity of colds after vita- oxidation of LDL cholesterol (the min C supplementation may be due prevention and “bad” cholesterol), especially in to the antihistaminic action of mega combination with vitamin E. Some doses of vitamin C. therapeutic use data has shown that vitamin C may also boost blood levels of HDL cho- Wound healing Dozens of prospective studies sug- lesterol (the “good” cholesterol), During a postoperative period, or gest that vitamin C plays a role in which is also considered positive for during healing of superficial wounds, preventing a variety of diseases. It is the prevention of heart diseases. supplemental vitamin C contributes also used to treat certain diseases in The risk of stroke may be reduced to the prevention of infections and orthomolecular medicine. As this by an adequate intake of vitamin C promotes skin repair. nutrient is important for a variety of through fruits, vegetables and sup- diseases, only a selection of them plements. However, due to the Blood pressure are presented here in detail. inconsistency of the data and its Several studies have shown a blood lack of specificity to vitamin C, the pressure lowering effect of vitamin C Cardiovascular diseases (CVD) interpretation of these results is diffi- supplementation at about 500 mg (heart disease and stroke) cult. per day due to improved dilation of The data for the CVD protective ben- blood vessels. efits of vitamin C are inconsistent. Cancer While some studies have failed to The role of vitamin C in cancer pre- find significant reductions in the risk vention has been studied extensive- of coronary heart disease (CHD), ly, and until now no beneficial effect Recommended numerous prospective cohort stud- has been shown for breast, prostate, Dietary Allowance ies have found inverse associations or lung cancer. However, a number between dietary vitamin C intake or of studies have associated higher (RDA) vitamin C plasma levels and CVD intakes of vitamin C with decreased risk. Vitamin C may protect coronary incidence of cancers of the upper arteries by reducing the build-up of digestive tract, cervix, ovary, blad- The recommended daily intake of der, and colon. Studies finding sig- vitamin C varies according to age, nificant cancer risk reduction by sex, risk group and criteria applied dietary intake recommended at least in individual countries. The RDAs in 5 servings of fruits and vegetables the USA for vitamin C were recently per day. Five servings of most fruits revised upwards to 90 mg/day for and vegetables provide more than men and 75 mg/day for women, 200 mg vitamin C per day. Just sig- based on pharmacokinetic data. For nificant cancer risk reductions were smokers, these RDAs are increased found in people consuming at least by an additional 35 mg/day. Higher 80 to 110 mg of vitamin C daily. amounts of vitamin C are also rec- ommended for pregnant (85 mg/day) Common cold and lactating women (120 mg/day). Numerous studies have shown a The RDAs are in a similar range in general lack of effect of other countries. Recent evidence prophylactic vitamin sets the estimate for the mainte- C supplementation nance of optimal health in the region on the incidence of of 100 mg daily. common cold, but they do show a moderate benefit in terms of the duration and severity of episodes in some groups, especially those who are exposed to sub- stantial physical and/or cold stress. The improve- 42 Safety Supplements and Uses in food food fortification technology As much as 6-10 g vitamin C per day (more than 100 times the RDA) Vitamin C is offered in conventional The food industry uses ascorbic acid has been ingested regularly by many tablets, effervescent and chewable as a natural antioxidant. This means people with no evidence of side tablets, time-release tablets, syrups, that ascorbic acid, added to food- effects. Although a number of possi- powders, granules, capsules, drops stuffs during processing or prior to ble problems with very large doses and ampoules, either alone or in packing, preserves colour, aroma of vitamin C have been suggested, multivitamin-mineral preparations. and nutrient content. This use of none of these adverse health effects Buffered vitamin C forms are less ascorbic acid has nothing to do with have been confirmed, and there is acidic, which can be an advantage its vitamin action. In meat process- no reliable scientific evidence that in terms of preventing gastric irrita- ing, ascorbic acid makes it possible large amounts of vitamin C (up to 10 tion. Vitamin C can also be used in to reduce both the amount of added g/day in adults) are toxic. In the year the form of injections (Rx). A number nitrite and the residual nitrite content 2000 the US Food and Nutrition of fruit juices, fruit flavour drinks and in the product. The addition of Board recommended a tolerable breakfast cereals are enriched with ascorbic acid to fresh flour improves upper intake level (UL) for vitamin C vitamin C. On average in Europe, its baking qualities, thus saving the of 2 g (2,000 mg) daily in order to vitamin C supplements provide 4-8 weeks of maturation flour would prevent most adults from experienc- between 5.8% and 8.3% of total normally have to undergo after ing osmotic diarrhoea and gastroin- vitamin C intake. milling. testinal disturbances. Industrial production The synthesis of ascorbic acid was achieved by Reichstein in 1933, and Current recommendations in the USA this was followed by industrial pro- duction five years later by Hoffman Dietary Reference Intakes* La Roche Ltd. (the vitamin division of Infants 6 months 40mg (Adequate Intake, AI) which is now DSM Nutritional Infants 7-12 months 50mg (AI) Products Ltd.). Today synthetic vita- Children 1-3 years 15mg min C, identical to that occurring in nature, is produced from glucose on Children 4-8 years 25mg an industrial scale by chemical and Children 9-13 years 45mg biotechnological synthesis. Males 14-18 years 75mg Females 14-18 years 65mg Males 19 years 90mg Females 19 years 75mg Pregnancy 18 years 80mg Pregnancy 19 years 85mg Lactation 18 years 115mg Lactation 19 years 120mg *The Dietary Reference Intakes (DRIs) are actually Allowances (RDAs). The RDA was established as a set of four reference values: Estimated Average a nutritional norm for planning and assessing Requirements (EAR), Recommended Dietary dietary intake, and represents intake levels of Allowances (RDA), Adequate Intakes (AI), and essential nutrients considered to meet adequately Tolerable Upper Intake Levels, (UL) that have the known needs of practically all healthy people replaced the 1989 Recommended Dietary 43 History Ca. 400 BC Hippocrates describes the symptoms of scurvy. 1747 British naval physician James Lind prescribes oranges and lemons as a cure for scurvy. 1907 Scurvy is experimentally produced in guinea pigs by Hoist and Frohlich. 1917 A bioassay is developed by Chick and Hume to determine the anti-scorbutic properties of foods. 1930 Szent-Györgyi demonstrates that the hexuronic acid he first isolated from the adrenal glands of pigs in 1928 is identical to vitamin C, which he extracts in large quantities from sweet pep- pers. 1932 In independent efforts, Haworth and King establish the chemical structure of vitamin C. 1932 The relationship between vitamin C and anti-scorbutic factor is discovered by Szent-Györgyi and at the same time by King and Waugh. 1933 In Basle, Reichstein synthesises ascorbic acid identical to natural vitamin C. This is the first step towards the vitamin's industrial production in 1936. 1937 Haworth and Szent-Györgyi receive a Nobel prize for their research on vitamin C. 1940 In a self experiment, Crandon proves the mandatory contribution of vitamin C in wound healing 1970 Pauling draws worldwide attention with his controversial bestseller “Vitamin C and the Common Cold”. 1975 Experimental studies in vitro illustrate the antioxidant and singlet- -79 oxygen quenching properties of vitamin C. 1979 Packer and coworkers observe the free radical interaction of vitamin E and vitamin C. 1982 Niki demonstrates the regeneration of vitamin E by vitamin C in model reactions. 1985 The worldwide requirement for vitamin C is estimated at 30,000- 35,000 tons per year. 1988 The National Cancer Institute (USA) recognises the inverse relationship between Vitamin C intake and various forms of cancer, and issues guidelines to increase vitamin C in the diet. 44 1998/99 Three studies show that supplementation with vitamin C can dramatically lower lead levels. 2004 A systematic review of thirty studies addressing the effect of supplemented vitamin C on the duration of colds revealed that there was a consistent benefit, with a reduction in duration of 8% to 14%. 2005 Levine calls for a re-evaluation of vitamin C as cancer therapy, especially intravenous vitamin C 2006 A 5 year Japanese study showed that the risk of contracting three or more colds in the five-year period was decreased by Tadeusz Reichstein 66% by daily intake of a 500-mg vitamin C supplement. Charles Glen King Albert Szent-Györgyi Linus Carl Pauling