The Minimum Requirement for Vitamin

Although the minimum requirement for vitamin C is firmly established, there are considerable discrepancies between the reference intakes published by different national and international authorities (see Table 13.3), with figures ranging between 30 to 90 mg per day. This is the result of the use of different criteria of adequacy and reflects differences of opinion as to what represents an adequate intake of vitamin C. It is possible to produce arguments to support reference intakes of between 30 to 100 mg per day. 

Carr and Frei (1999b) reviewed studies of vitamin C intake associated with reduced risks of cancer and cardiovascular disease and suggested that, by this criterion, the average requirement was 90 to 100 mg per day, giving a reference intake of 120 mg per day. 

The minimum requirement for vitamin C was established in the Sheffield study (Medical Research Council, 1948), which showed that an intake of marginally less than 10 mg per day was adequate to prevent the development of scurvy or to cure the clinical signs. Results from the Iowa study (Baker et al., 1969, 

European Union FAO, Food and Agriculture Organization WHO, World Health Organization. 

Sources Department of Health, 1991 Scientific Committee for Food, 1993 Institute of Medicine, 2000 FAO/WHO, 2001. 

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It is assumed that in order to have vitamin A activity a molecule must have essentially one-half of its structure similar to that of (i-carotene with an added molecule of water at the end of the lateral polyene chain. Thus, P-carotene is a potent provitamin A to which 100% activity is assigned. An unsubstituted p ring with a Cii polyene chain is the minimum requirement for vitamin A activity. y-Car-otene, a-carotene, P-cryptoxanthin, a-cryptoxanthin, and P-carotene-5,6-epoxide aU have single unsubstimted rings. Recently it has been shown that astaxanthin can be converted to zeaxanthin in trout if the fish has sufficient vitamin A. Vitiated astaxanthin was converted to retinol in strips of duodenum or inverted sacks of trout intestines. Astaxanthin, canthaxanthin, and zeaxanthin can be converted to vitamin A and A2 in guppies. ... 

Approximately 0.05 to 0.2% of vitamin > 2 stores are turned over daily, amounting to 0.5—8.0 )J.g, depending on the body pool size. The half-life of the body pool is estimated to be between 480 and 1360 days with a daily loss of vitamin > 2 of about 1 )J.g. Consequentiy, the daily minimum requirement for vitamin B22 is 1 fig. Three micrograms (3.0 J.g) vitamin B22 are excreted in the bile each day, but an efficient enterohepatic circulation salvages the vitamin from the bile and other intestinal secretions. This effective recycling of the vitamin contributes to the long half-life. Absence of the intrinsic factor intermpts the enterohepatic circulation. Vitamin > 2 is not catabolized by the body and is, therefore, excreted unchanged. About one-half of the vitamin is excreted in the urine and the other half in the bile. 

Subsequently, the functions of the vitamin were better established and requirements for the vitamin were set. Riboflavin is an Integral part of two coenzymes, flavin-5 -phosphate (FMN) and flavin adenine dinucleotide (FAD), which function in oxidation/reductlon reactions. Indeed, riboflavin is an enzyme cofactor which is necessary in metabolic processes in which oxidation of glucose or fatty acid is used for production of adenosine triphosphate (ATP) as well as in reactions in which oxidation of amino acids is accomplished. The minimum requirement for riboflavin has been established as that amount which actually prevents the signs of deficiency. A range of intakes varying from 0.55 to 0.75 mg/day of riboflavin has been established as the minimum amount which is required to prevent appearance of deficiency signs. 

Based on the body content of 15 pmol (3.7mg) of vitamin Bg per kilogram body weight, and the rate of weight gain, the minimum requirement for infants over the first 6 months of life would appear to be 100 pg (417 nmol) per day to establish tissue reserves. 

Vitamin C cannot be synthesized in the human body and must be obtained from the diet (e.g., citrus fruits, broccoli, turnip greens, sweet peppers, tomatoes) or by taking synthetic vitamin C (e.g., vitamin C tablets, high-C drinks, and other vitamin C-fortified commercial foods). The minimum recommended adult daily requirement of vitamin C to prevent scurvy is 60 mg. Some people, among them the late Linus Pauling, twice Nobel Laureate, suggested that very large daily doses (250 to 10,000 mg) of vitamin C could help prevent the common cold, or at least lessen the symptoms for many individuals. No reliable medical data support this claim. At present, the human quantitative requirement for vitamin C is still controversial and requires further research. 

Very few direct studies have been performed to determine human vitamin A requirements. In the Sheffield study (Hume and Krebs, 1949), 16 subjects were depleted of vitamin A for 2 years only three subjects showed clear signs of impaired dark adaptation. One of these subjects was repleted with 390 /rg of retinol per day, which resulted in a gradual restoration of dark adaptation the other two subjects received /3-carotene. On this basis, the minimum requirement was presumed to be 390 /rg, and the reference intake was set at 750 /rg. 

There is a variety of estimates of the body pool of vitamin Be. Short-term studies with isotopic tracers suggest a total body content of between 160 to 600 ixmo (40 to 150 mg), with a half-life of 33 days, suggesting a minimum requirement for replacement in the wide range between 0.6 to 2.27 mg per day. 

Other investigators have found larger amounts of ascorbic acid were necessary to maintain normal concentrations of the vitamin in blood. For monkeys, 10 (63) and 25 (35) mg of ascorbic acid/kg of body weight were proposed as the minimum required amounts. Recent experiments showed that the trained monkey required only 3-6 mg of ascorbate/kg of body weight (120). Young monkeys (sexually imma-... 

Vitamin A is an essential substance for healthy vision and skin, but sometimes too much of this good thing creates problems. A relationship between excessive vitamin A intake during pregnancy and birth defects has been recognized for some time. However, the minimum amount of vitamin A required to produce harmful effects is now believed to be much lower than was previously thought. According to a recent study, the consumption of vitamin A at or above 10,000 international units per day was linked to birth defects. A vitamin international unit (lU) is a measure of vitamin activity, determined... 

Since the discovery of ascorbic acid and its identification with vitamin C there has been continued effort to determine the human requirement for this essential nutrient. Evidence indicates that the minimum daily intake needed to prevent scurvy is about 10 mg. The daily allowance recommended by health authorities for adults ranges from 20 mg in the United Kingdom to 75 mg in West Germany. The Food and Nutrition Board of the U.S. National Research CounciP recommends values ranging from 35 mg for an infant to 60 mg for a 70-kg man, as designed for the maintenance of good nutrition of practically all healthy people in the U.S.A. The recommended allowances are said to provide a generous increment for individual variability and a surplus to compensate for potential losses in food. 

In the United Kingdom, there is a distinct separation of food supplements and herbal medicines. The Food Standards Agency developed the Food Standard Act of 1999 and is responsible for protection of public health. The Food Supplement Directive 2002/46/EC, which harmonizes European Community legislation on food supplements, was published in 2002. This directive is stricter than existing UK standards and regulations but is relatively more liberal than what exists in other European countries. The directive defines the term food supplements, contains a list of vitamin and mineral sources that may be used in the manufacture of food supplements, states labeling requirements, and, in the future, will provide a framework for maximum and minimum levels for vitamins and minerals in food supplements. Herbals and botanicals are not discussed in this directive. 

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