Recommended dietary allowances RDA for vitamins

Table 2 Hsts the Recommended Dietary Allowances (RDA) for vitamin K. Although manufacture by intestinal bacteria represents a significant source of plasma menaquinone concentrations, rehance on this source alone is not sufficient to maintain healthy concentrations of menaquinone. Consequendy, dietary supplementation is necessary (76).

Recommended dietary allowances (RDA) for vitamins are recommended intake of various vitamin to ensure the good health of a high proportion of the human population. The RDA values quoted below refer to the United States population (Whitney and Rolfes, 1996). Reference nutrient intake... 

The recommended dietary allowance (RDA) for vitamin D is 5 fig (200 IU)/d, but this value includes casual exposure to sunlight without regard to lifestyle or climate. For individuals who do not receive adequate sunlight because of illness, advanced age, or are otherwise shut in, the actual daily requirement for vitamin D3 could be as much as 15 fig/d. Vitamin D3 deficiency also may occur with chronic biliary obstruction and steatorrhoea limiting intestinal absorption of vitamin D3 and lead to osteomalacia [44], Another factor is the increased use of sunscreens among Western societies, that limits the penetration of UV photons to the site of vitamin D3 synthesis [41,45,46],... 

The current recommended dietary allowance (RDA) for vitamin C (L-ascor-bate) for adult non-smoking individuals is 60 mg day which is based on a mean requirement of 46 mg day to prevent the deficiency disease scurvy [ 14]. It was shown that ascorbate uptake by neutrophils, monocytes, and lymphocytes saturate with a daily supplementation of 100 mg ascorbate and that these cells contain concentrations at least 14-fold higher than those in plasma. Bioavailability was complete for 200 mg of vitamin C as a single dose. 

The amount of vitamin E required by the body depends upon its size and the amount of polyunsaturated fats in the diet, as vitamin E is needed to protect these fats from oxidation. The requirement for vitamin E depends upon intake of refined oils, fried foods, or rancid oils. Supplemental estrogen or estrogen imbalance in women increases the need for vitamin E, as does air pollution. The recommended dietary allowance (RDA) for vitamin E is really quite low, many people do not consume this in their diet alone. Table 19.1 lists the RDAs and tolerable upper intake levels (ULs) for vitamin E. The new recommendations for vitamin E are expressed as milligrams of RRR-a-tocopherol equivalents. Dietary supplements of vitamin E are labeled in terms of international units (lU). 1 mg of synthetic vitamin E (a//-rac-a-tocopheryl acetate is equivalent to 1 lU vitamin E, but only 0.45 mg RRR-a-tocopherol. 1 mg of natural vitamin E (RRR-a-tocopherol) provides 1.5 lU. For the LIE, the Food and Nutrition Board recommended 1000 mg of any a-tocopherol form, which is equivalent to 1500 lU RRR- or 100 lEI all-rac-a-tocopherol (Food and Nutrition Board, 2000 Hathcock et al., 2005 Combs, 2008). 

Table 2 Recommended dietary allowances (RDA) for vitamin A in micrograms ( g), retinol activity equivalents (RAE) and international units (lU), and tolerable upper intake levels (UL, pg retinol day" ) for children and adults ...

Both Tables 6.1 and 6.2 list the recommended dietary allowances (RDA) for each vitamin. These are recommended by the Food and Nutrition Board of the National Academy of Sciences. The values given are designed to maintain a... 

For several years the recommended dietary allowance (RDA) of vitamin C has varied from country to country. It was recently increased from 45 to 60 mg/d in the United States (J). Probably, healthy people in their active ages normally ingest this and even larger amounts through their dietary habits, whereas elderly people, diseased people, or people under special circumstances like alcoholics may be at an actual risk and need supplementation to meet the basal needs for the vitamin. 

In addition to the USDA, the National Academy of Sciences Food and Nutrition Board (http //www.iom.edu) publishes the U.S. Recommended Dietary Allowance (RDA) for daily dose requirements of each vitamin (Table 9-1). 

Vitamins and minerals are required for the body to function properly. Each day we need to eat a balanced diet that supplies us with the sufficient amount of vitamins and minerals to remain healthy. Our diet should contain grains, vegetables, fruits, milk, meat and beans. The portion of each varies depending on our age and gender. The USDA Web site publishes the Recommended Dietary Allowance (RDA) for daily dose requirement of each vitamin. 

The vitamin is obtained from the diet in the form of nicotinic acid, nicotinamide, NAD/NADP and tryptophan. The Recommended Dietary Allowance (RDA) for adults is 16mg/day of niacin equivalents for men and 14mg/day for women (Food and Nutrition Board 1998). 

Since animals and humans are unable to biosynthesize vitamin E, they have to rely on an external supply of it through their diet. Consequently, animal tissues with the exception of adipose tissue and liver are poor in tocopherols. Tocotrienols are not resorbed to a significant extent. The recommended dietary allowance (RDA) of vitamin E is linked to the intake of polyunsaturated fatty acids (PUFAs) and is of the order of 10 mg a-tocopherol equivalents per day. a-Tocopherol is the predominant form in plasma (88%), whereas the P and y forms contribute for only 2% and 10%, respectively, to the vitamin E levels. 8-Tocopherol is only detected after massive ingestion of, e.g., soybean fat emulsions. Tocopherols are nonspeciflcally transported by plasma P-lipoproteins and stored in membranes and adipose tissue. 

Most forms of carrots are high in water content (88 to 92%) and low in calories (29 to 42 kcal per 100 g). However, they are excellent sources of vitamin A, since a 3 1/2 oz (100 g) serving provides more than double the Recommended Dietary Allowance (RDA) for adults. 

The Food and Nutrition Board of the Institute of Medicine revised the Recommended Dietary Allowance (RDA) of vitamin A in 2001 as 900 retinol activity equivalents (RAF) for men and 700 RAF for women. The RAF was introduced to avoid the ambiguity of international units (lU), which arises because 1 lU of vitamin A (0.3 pg) and 1 lU of the vitamin A precursor (provitamin A) all-tra s-/ -carotene (0.6 pg) do not have the same biological activity. Rather, 6 lU of /3-carotene and 12 lU... 

Recommended dietary allowances (RDA) for the US and Canada were recently revised by the Institute of Medicine (lOM). Owing to the serious, potentially irreversible, effects caused by an excess of vitamin A, guidelines were also established for a tolerable upper intake level (UL), defined as the highest intake of a nutrient that is likely to pose no risk of adverse health effects in nearly all healthy individuals. The 2001 RDA and UL for vitamin A for various life stages are listed in Table 2. 

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. 

No significant quantity of the macronutrients nor of the vitamins for which U.S. Recommended Dietary Allowance (RDA) have been established can be obtained from the consumption of a cup of tea.110 The water-soluble B vitamins present are easily extractable. Eight percent extractabil-ity for a representative black tea blend is assumed.110... 

Recommended Dietary Allowance (RDA), 17 652 25 784-787 of ascorbic acid, 25 772 defined, 25 784 for vitamins, 25 785t Recommended exposure level (REL), hydrazine, 13 590... 

A healthy diet with proper nutrition is essential for maintaining good overall health. Since the discovery of vitamins earlier in this century, people have routinely been taking vitamin supplements for this purpose. The Recommended Dietary Allowance (RDA) is a frequently used nutritional standard for maintaining optimal health. The RDA specifies the recommended amount of a number of nutrients for people in different age and sex groups. The National Research Council s Committee on Diet and Health has proposed a definition of the RDA to be that amount of a nutrient which meets the needs of 98% of the population. 

Reference Intakes (DRIs). In the past, the recommended dietary allowances (RDAs), which are the levels of intake of essential nutrients that are considered to be adequate to meet the known nutritional needs of practically all healthy persons, were the primary reference value for vitamins and other nutrients. The DRIs also include other reference values, such as the estimated average requirement (EAR) and the adequate intake (AI). The RDA, EAR, and AI reference standards define nutritional intake adequacy. Since these recommendations are given for healthy populations in general and not for individuals, special problems, such as premature birth, inherited metabolic disorders, infections, chronic disease, and use of medications, are not covered by the requirements. Separate RDAs have been developed for pregnant and lactating women. Vitamin supplementation may be required by patients with special conditions and for those who do not consume an appropriate diet. 

As noted, vitamin C is needed for the production of collagen in the body, but it is also essential in the production of certain hormones such as dopamine and adrenaline. Ascorbic acid is also essential in the metabolism of some amino acids. It helps protect cells from free radical damage, helps iron absorption, and is essential for many metabolic processes. The dietary need of vitamin C is not clearly established, but the U.S. National Academy of Science has established a recommended dietary allowance (RDA) of 60 mg per day. Some groups and individuals, notably Linus Pauling in the 1980s, recommend dosages as high as... 

The fat-soluble vitamins comprise vitamins A, D, E, and K, whose biological activities are attributed to a number of structurally related compounds known as vitamers. Also included are those carotenoids that are precursors of vitamin A. Recommended dietary allowances (RDAs) based on human epidemiological and experimental animal studies have been published in the United States for vitamins A, D, E, and K (1). Other countries and international bodies have compiled similar recommendations. In the United States and Canada, fluid milk is supplemented by law with vitamin D to a level of 400 international units per quart (10 /zg/0.95 L) to meet the RDA of 10 p%. Other commodities, such as margarine, milk products, ready-to-eat breakfast cereals, and dietetic foods, are commonly supplemented with vitamins A, D, and E. Except for infant formulas, vitamin K is not added to foods. The addition of vitamins to a particular processed food is intended to provide a specific proportion of the RDA. 

Table 1.7 Recommended Dietary Allowances (RDAs) and Acceptable Intakes for Vitamins, U.S./Canada, 1997- 2001 ... 

Vitamins are complex biochemically and functionally and may be classified many ways. This chapter acknowledges the traditional solubility model but focuses on functionality. Un-fortunately,the loose regulation of nutritional products in the United States has led to misleading promotion of these items to the lay public, such that individuals are confused as to what can be called a vitamin. General criteria for deciding if a substance truly is a vitamin are presented. Another problem is to decide r whether a patient actually has a vitamin defi-J ciency. As noted in the next section, this can be l cornplex question. Finally, deciding how ifaich of a particular vitamin should be consumed has moved from the familiar Recommended Dietary Allowance (RDA) to four different ways to evaluate vitamin requirements and consumption. These are called the Dietary Reference Intakes (DRIs). 

Diketogulonate cannot be reduced back to ascorbate. Most animals synthesize ascorbate using the path shown in Fig. 7.7, but primates including humans have accumulated mutations in the gene for L-gulonolactone oxidase and cannot synthesize ascorbate de novo. They require a dietary source of vitamin C to compensate for the gradual loss of dehy-droascorbate. The current Recommended Dietary Allowance (RDA) from the US Food and Drug Administration is 60-95 mg/day. 

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