Vitamin recommended daily intake

Recommended Daiiy Aiiowance (RDA) an older standard for the FDA-recommended daily intake of a vitamin. 

Selenium is readily available in a variety of foods including shrimp, meat, dairy products, and grains, with a recommended daily intake of 55 to 70 jug. It occurs in several forms with Se+6 being biologically most important. Selenium is readily absorbed by the intestine and is widely distributed throughout the tissues of the body, with the highest levels in the liver and kidney. It is active in a variety of cellular functions and interacts with vitamin E. Selenium appears to reduce the toxic effects of metals such as cadmium and mercury and to have anticarcinogenic activity. Selenium produces notable adverse effects both in deficiency and excess thus recommended daily intake for adults is approximately 70 Jg/day but should not exceed 200 pg/day. 

The main sources of vitamin C are green vegetables and citrus fruit. Animal tissue contains vitamin C, mainly in the kidneys and liver. The level of vitamin C in food is rapidly reduced during cooking or storage due to oxidation or water dissolution. It is added to food as an antioxidant (with no specified limit on the level of use) or as a supplement (with a maximum recommended daily intake of 3000mg/day). The forms admitted are L-ascorbic acid (AA), L-ascorbyl 6-palmitate, sodium, calcium, or potassium L-ascorbate [403]. 

The primary roles and the recommended daily intake of major and trace minerals are listed in Table 38-3. Similar to vitamins, these minerals are typically obtained from dietary sources. Specific minerals may likewise be included in various multivitamins and other dietary supplements, with the intent that these minerals will promote good health and prevent disease. Again, there is generally no need for mineral supplements for most people eating a reasonably balanced diet. On the other hand, mineral supplements can be helpful in specific situations where the body s need for a mineral may exceed dietary supply. Some examples of appropriate supplementation include calcium supplements for people with osteoporosis (see Chapter 31), potassium supplements for people on diuretics (see Chapter 21), and iron supplements for people with certain anemias. Hence, mineral supplements may be helpful in certain individuals, but the dose and type of supplement should be adjusted carefully. 

Although absolute vitamin deficiency (e.g., beriberi, pellagra, scurvy) may be relatively rare in developed coiuitries, malabsorption, poor nutritional habits, or other fectors may lead to such situations. In feet, many Americans may be vitamin deficient based on recommended daily allowance or recommended daily intake.The interested reader is referred to the U.S. Department of Agriculture fiaod and nutrition information center fiar recommended daily aUonrance and recommended daily intake (http //fiiic.nal.usda.gov/).These are also summarized in Table 17-1 as DRI ralues. 

Vitamins Weight in mcg/mg Recommended Daily Intake (a) Maximum Allowed % of (a) ... 

Vitamin D is associated with biological functions, such as bone formation, immune system responses, cell defences and anti-tumour activity.615,616 Vitamin D comes in two closely related forms, vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol), and their metabolites. Both vitamin D2 and D3 occur naturally in some foods. However, vitamin D3 (63) can also be synthesized in skin cells called keratinocytes from 7-dehydrocholesterol (provitamin D 64), which undergoes a photochemical six-electron conrotatory electrocyclic ring opening at 280nm to previtamin D3 (41 see also Scheme 6.8), which spontaneously isomerizes to 63 in a thermal antarafacial hydride [l,7]-sigmatropic shift (Scheme 6.21). Both vitamin D2 and D3 are subsequently converted to active hormone 1,25-D by enzymes in several steps. The recommended daily intake of vitamin D for humans is 5 10 pg per day. For example, 15 ml of fish liver oils and 100 g of cooked salmon contain approximately 35 and 10 pg... 

Rats that are deprived of vitamin E become infertile, but the reasons for this effect are unknown. Vitamin E is known to prevent the oxidation of double bonds in the hydrocarbon tails of membrane lipids, and this may be its major function. Because oxidation reactions accelerate aging, some researchers believe that vitamin E may help to retard the aging process. The RDA for vitamin E is expressed in a-tocopherol equivalents (a-TE) because this is the most active form of vitamin E. The recommended daily intake is 10 a-TE for males and 8 a-TE for females. This is roughly the amount of vitamin E in a tablespoon of vegetable oil. 

The tablets sold in pharmacies, which are used to prevent or treat colds, usually contain much larger amounts (200-1000 mg) of ascorbic acid. Could this high dose be harmful Does it make sense to exceed the physiologically necessary dosage or to take megadoses of vitamin C A general answer to the first question is given in a separate stoiy 3.14). For present purposes, it suffices to state that the approved ascorbic acid products are safe even if they contain several times of the recommended daily intake of vitamin C. 

It seems that the daily intake of cobalt by humans is about 5-45 ixg [5-7]. The recommended daily intake of vitamin B12 for adults is 3 ji.g (0.13 xg of Co) [5,8], taking into account that only 50% is absorbed in the intestine [9]. 

Plants do not contain vitamin A as such, although many of them include a variety of highly pigmented carotenoids. Some of these, namely the a-, and y-carotenes, can be converted into vitamin A in the body and hence are provitamins, -carotene is the most active of these. It is a symmetrical compound and can be converted into two molecules of vitamin A in the intestinal wall and in the liver, but since /3-carotene is poorly absorbed and only partially converted, its utilization efficiency is only about one-sixth. Unchanged carotene is found in the plasma and in the body fat. Vitamin A and carotene are both fairly stable and not much affected by cooking, although some activity may be lost if fats become rancid. The recommended daily intake for adults is 750 pg (5000 International Units) of retinol, 6 x 750 pg of/3-carotene or 12 x 750 pg of a- and y-carotene. 

The recommended daily intake of pantothenic acid in infants under 6 months of age is 1.7 mg, and is 2 mg in children from 6 to 12 months, 3 mg in children from 4 to 8 years, 4 mg in children from 9 to 13.5 years, 5 mg in adolescents and men and 6 mg in women (7 mg in lactating women). Normal dietary intake of this vitamin is 6-12 mg per day. Cases of deficiency, which us manifested mainly by skin irritation andparaesthesia (a tingling anditching sensation), are not common. 

For certain vitamins and minerals there are indications that an intake beyond the recommended daily intake required to prevent deficiencies may be beneficial for the prevention of certain diseases. For instance, it has been established that increased intake of folic acid during pregnancy can reduce the incidence of neural tube defects in the newborn. There is also evidence to suggest that the risk of developing cardiovascular disease may be decreased by increasing vitamin E and folic acid intakes, but this remains to be firmly estabhshed. Calcium-enriched products are also believed to have a role to play in bone health. These are just a few of the growing number of links being made between vitamins and minerals and disease risk reduchon. 

Zinc is the prosthetic group for many enzymes. It is also incorporated into the receptor proteins for steroid and thyroid hormones, calcitriol and vitamin A. Recommended daily intake of zinc is 10 mg/day. Zinc is found in all tissues of the body, but it is particularly high in the bone, liver and kidney. Zinc deficiency causes growth retardation, decreased wound healing and hypogonadism (i.e. much delayed puberty). It is only normally seen in populations whose diet is based on unleavened wholemeal bread, because wheat flour does not provide much zinc, and that which is available is bound to phytate. Phytate also inhibits the absorption of iron. Zinc depletion may also be caused by drugs such as thiazide and loop diuretics, and alcohol. Zinc deficiency can be successfully treated with replacement zinc therapy. 

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