Ascorbic acid vitamin dietary sources

See also Antioxidants Observational Studies Intervention Studies. Ascorbic Acid Physiology, Dietary Sources and Requirements. Carotenoids Chemistry, Sources and Physiology Epidemiology of Health Effects. Copper. Folic Acid. Riboflavin. Selenium. Vitamin E Physiology and Health Effects. Zinc Physiology. 

Ascorbic acid. The potato is a significant dietary source of ascorbic acid (vitamin C), which is necessary for normal collagen formation and which acts as an antioxidant. In... 

Vitamin C occurs as L-ascorbic acid and dihydroascorbic acid in fruits, vegetables and potatoes, as well as in processed foods to which it has been added as an antioxidant. The only wholly undisputed function of vitamin C is the prevention of scurvy. Although this is the physiological rationale for the currently recommended intake levels, there is growing evidence that vitamin C may provide additional protective effects against other diseases including cancer, and the recommended dietary allowance (RDA) may be increased in the near future. Scurvy develops in adults whose habitual intake of vitamin C falls below 1 mg/d, and under experimental conditions 10 mg/d is sufficient to prevent or alleviate symptoms (Bartley et al., 1953). The RDA is 60 mg per day in the USA, but plasma levels of ascorbate do not achieve saturation until daily intakes reach around 100 mg (Bates et al., 1979). Most of the ascorbate in human diets is derived from natural sources, and consumers who eat five portions, or about 400-500 g, of fruits and vegetables per day could obtain as much as 200 mg of ascorbate. 

Citrus juice is rich in ascorbic acid and, therefore, is an important dietary source of this essential vitamin. Our studies were aimed at defining whether vitamin C from citrus sources is comparable with the synthetic vitamin in terms of bioavailability and intestinal absorption. These studies were conducted using human volunteers and guinea pig experimental models (1, 2). 

The antioxidants studied can be classified into two broad types phenolic antioxidants and non-phenolic antioxidants. Phenolic antioxidants have been found to be more promising as they are obtained from dietary sources.Vitamin E (a-tocopherol), the first known chainbreaking antioxidant, is also an o-methoxy phenol. Pulse radiolysis studies of vitamin E and its water-soluble analogue, trolox C, have been reported several years ago. a-tocopherol reacts with almost all the oxidizing free radicals, and the phenoxyl radicals produced during oxidation reactions absorb at -460 nm (Fig. 1). The regeneration reaction of a-tocopherol phenoxyl radicals back to a-tocopherol by water-soluble antioxidant ascorbic acid was also first reported by pulse radiolysis method. The one-electron reduction potential of vitamin E is -0.48 V vs. NHE. Both a-tocopherol and trolox C are used as standards for evaluating the antioxidant ability of new compounds. 

For those, undoubtedly the majority even in Western countries, who rely on natural dietary sources of the vitamin, care is needed in culinary practice if much of the ascorbic acid is not to be lost. As seen in Chapter 5 the fine cutting of vegetables releases ascorbic acid oxidase which will destroy the vitamin and the use of excessive water for cooking will leach it out of the food. Overcooking and the addition of sodium bicarbonate, thankfully by now little practised, also destroy the vitamin by oxidation which is particularly rapid in cooking pots made of copper. For the human infant, as for any mammal, mother s milk is a whole food and that includes vitamin C at a level of 3.0-5.5 mg%. Bovine milk is much less rich and needs supplementation for feeding to human infants. 

Increased absorption is almost certainly the cause of the raising of the blood and tissue levels of vitamin B12 by sorbitol and some other substances. Intestinal synthesis is responsible for the far more dramatic sparing of other B vitamins by sorbitol, ascorbic acid, and several other substances, so that animals become completely independent of dietary sources of these vitamins. Finally, the ability of ascorbic acid to prolong the life of animals deficient in folic acid is very probably due to the promotion of the synthesis of this vitamin in the tissues. 

On the other hand, the situation is now fairly clear with those substances which make an animal independent of dietary sources of at least several of the B. vitamins. The mechanism has been worked out best for starcih, sorbitol, and ascorbic acid, insofar as they spare thiamine, but there is no reason to suppose that the same mechanism does not apply also to the other carbohydrates and allied substances which produce the same effect and to the other vitamins which are spared. 

Vegetables are important sources of vitamin C (ascorbic acid), jS-carotene, certain B vitamins, minerals, dietary fiber and protein, with different vegetable types being particularly rich in particular nutrients. 

Although IDA can be caused by loss of blood or by poor absorption of iron, the most common cause is insufficient iron in the diet. Dietary iron comes from such sources as meat, eggs, leafy green vegetables, dried beans, and dried fruits. Some breakfast cereals, such as Total, are fortified with iron in the form of iron metal, also known as elemental or reduced iron. The absorption of dietary iron can be enhanced by the intake of vitamin C (ascorbic acid). When the diet fails to provide enough iron, a nutritional supplement may be necessary to prevent a deficiency. Many supplements provide iron in the form of a compound called rroits- sulfate. 

Ascorbic acid is one of the most easily destroyed of vitamins, by heat and air. Destruction also seems to occur in the intestinal tract. As with thiamine and some other vitamins, the urinary excretion of ascorbic acid increases as the dietary intake increases so that there must be a point at which it is no longer economically sound to add it to the diet. Synthesis of ascorbic acid takes place in the bodies of most species man, monkeys, and guinea pigs need a dietary source. 

The only species known definitely to require a dtetary source of vitamin C are man, monkeys and guinea pigs. It is possible that in mice, rabbits, swine and cattle vitamin C is required under certain conditions (45). A report by Philipps, et al. (133) indicates that dietary ascorbic acid is necessary for reproduction of cattle. These authors found that cows which had failed to reproduce conceived after injections of ascorbic acid. 

Dietary Reference Intake (DRI) of Cu, 17-18% of the DRI of K, P, and Fe, and between 5 and 13% of the DRI of Zn, Mg, and Mn (Table 5.1). Potatoes are generally not rich in Ca, but can be a valuable source of trace elements, such as Se and I, if fertilized appropriately (Eurola et al., 1989 Poggi et al., 2000 Turakainen et al., 2004 Broadley et al., 2006). Moreover, since potato tubers have relatively high concentrations of organic compounds that stimulate the absorption of mineral micronutrients by humans, such as ascorbate (vitamin C), protein cysteine and various organic and amino acids (USDA, 2006), and low concentrations of compounds that limit their absorption, such as phytate (0.11-0.27% dry matter Frossard et al., 2000 Phillippy et al., 2004) and oxalate (0.03% dry matter Bushway et al., 1984), the bioavailability of mineral elements in potatoes is potentially high. 

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