Vitamin reference intakes

Eood and Nutrition Board, Institute of Medicine (2001) Dietary reference intakes. Vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. National Academy Press, Washington, DC... 

Institute of Medicine, Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc, National Academies Press, Washington, 2001. 

Standing Committee of the Scientific Evaluation of Dietary Reference Intakes, Food and Nutrition Board, and Institute of Medicine (1997). In "Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride." National Academy Press, Washington, DC. 

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. 

Institute of Medicine. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin Bg, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington National Academy, 1998. 

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. 

Dietary Reference Intakes for vitamins and minerals in individuals one year and older. EAR = Estimated Average Requirement RDA = Recommended Dietary Allowance ... 

Food and Nutrition Board. 2000. Vitamin E. In Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids A Report of the Panel on Dietary Antioxidants and Related Compound, pp. 193-194. National Academy Press, Washington, D.C. 

Absence of reported adverse effects does not mean that there is no potential for adverse effects from high intake. Caution should still be used when taking doses well in excess of the recommended daily amounts. Adapted from Institute of Medicine of the National Academies [www.iom.edu) Food Nutrition > Dietary Reference Intakes > DRI Tables > Vitamins. 

Table 1.6 Population Reference Intakes of Vitamins, European Union, 1993... 

Adequate Intake For some vitamins, notably biotin (Section 11.5) and pantothenic acid (Section 12.6), dietary deficiency is more-or-less unknown, and there are no data from which to estimate average requirements or derive reference intakes. In such cases, the observed range of intakes is obviously more than adequate to meet requirements, and the average intake is used to calculate an adequate intake figure. 

Reference Intakes for Infants and Children For obvious ethical reasons, there have been almost no experimental studies of the vitamin requirements of infants and children. For infants, it is conventional to use the nutrient yield of breast milk and assume that this is equal to or greater than requirements. Although this is termed an RNI in U.K. tables (Table 1.5), in the U.S./Canadian tables (Table 1.7), it is more correctly referred to as an acceptable intake. 

Tolerable Upper Levels of Intake A number of the vitamins are known to be toxic in excess. For most, there is a considerable difference between reference intakes that are more than adequate to meet requirements and the intake at which there may he adverse effects, although for vitamins A (Section 2.5.1) and D (Section 3.6.1) there is only a relatively small margin of safety. 

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. 

An alternative approach to determining requirements is to measure the fractional rate of catabolism of the vitamin by use of a radioactive tracer, then determine the intake that would be required to maintain an appropriate level of liver reserves. As discussed in Section2.2.1.1, when the liver concentration rises above 70 /rmol per kg, there is increased activity of the microsomal oxidation of vitamin A and biliary excretion of retinol metabolites. The fractional catabolic rate is 0.5% per day assuming 50% efficiency of storage of dietary retinol, this gives a mean requirement of 6.7 /rg per kg of body weight and a reference intake of 650 to 700 /rg for adult men (Olson, 1987a). Reference intakes for vitamin A are shown in Table 2.4. 

Dietary vitamin D makes little contribution to status, and the major factor is exposure to sunlight, a conclusion that is supported by the two-fold seasonal variation in plasma calcidiol in temperate regions (see Table 3.2). There are no reference intakes for young adults in the United Kingdom and Europe for house-bound elderly people, the reference intake is 10 /rg per day, based on the intake required to maintain a plasma concentration of calcidiol of 20 nmol per L (see Table 3.5). This will almost certainly require supplements of the vitamin, because average intakes are less than half this amount. The U.S./Canadian adequate intake is 5 /xg per day up to age 50, increasing to 10 /xg between 51 to 70, and 15 /xg over 70 years of age (Institute of Medicine, 1997). 

D supplements are less at risk of developing the disease. It is not known how vitamin D protects against the development of diahetes, hut it may he hy modulation of the differentiation of lymphocytes involved in the autoimmune destruction of pancreatic -islet cells. The protective dose is above current reference intakes and indeed may he above the tolerable upper intake of 25 //g per day for infants (Harris, 2002). 

The U.S./Canadian Dietary Reference intakes report (Institute of Medicine, 2000) departed from tradition by considering only the contribution of the 2R isomers to vitamin E intake, and proposed an equivalence of 0.45 iu per mg for synthetic all-rac-a-tocopherol, although in consideration of upper tolerable levels of intake (Section 4.6.1), they considered the contribution of aU isomers equally However, although the 2S isomers have a shorter half-life than -tocopherol in the circulation, and hence a lower apparent biological availability, they are active in animal biological assays (Hoppe and Krennrich, 2000). 

Horwitt (2001) has criticized this high reference intake, noting that it was based on reinterpretation of the same data as had been provided to the committee in 1998, which set a lower RDA. Data were from studies that he had performed (Horwitt, 1960), andhe notes that to provide a diet rich in polyunsaturated fatty acids and low in vitamin E, the oils had been oxidized to remove vitamin E, and therefore contained large amounts of oxidized lipids that would increase apparent vitamin E requirements. 

---