INDEX vitamin requirements

Compliance with the content uniformity requirements for vitamins and minerals in multivitamin-mineral combination products may be determined by measuring the distribution of a single index vitamin or a single index mineral present in the product. Fohc acid is the index vitamin when present in a multivitamin formulation. For formulations that do not contain folic acid, cyanocobalamin is the index vitamin. If neither fohc acid nor cyanocobalamin is present in the formulation, the index vitamin is vitamin D and in the absence of vitamin D, the index vitamin is vitamin A. If none of the above four vitamins is present in the formulation, the vitamin labeled in the lowest amount is used as the index for content uniformity. 

In a typical multivitamin-mineral combination product consisting of 10-15 ingredients, it is neither practical nor necessary to require in vitro demonstration of each and every vitamin and mineral. Consequently, in a unique approach to establishing in vitro dissolution for multivitamin-mineral combination products, an index vitamin and an index mineral are identified as markers for dissolution. In an attempt to account for the many different permutations of vitamins and mineral combinations, a hierarchy of index vitamins and index minerals was arrived at and specified (5). Table 1 shows the hierarchy of index vitamins and minerals specified for demonstration of dissolution requirement in the nutritional supplements monographs in USP 25-NF20. 

In view of the reported growing importance ascribed to folic acid deficiency in the prevention of various disease conditions, such as neural tube defects, megaloblastic anemia, colon cancer, and colorectal cancer, a dissolution requirement is specified for folic acid when it is present in multivitamin-mineral combination products. Currently, the dissolution standard required in the official articles of dietary supplements (including vitamin-mineral combination products) places folic acid outside the index vitamin hierarchy. Therefore, a mandatory dissolution test for folic acid is required that is independent of and in addition to the mandatory index vitamin test for multivitamin preparations containing folic acid. 

The first grouping is a mix of fat-soluble compounds that function as hormones, co-factors, and membrane components. Fat-soluble vitamins separate on a Cis column in 80% acetonitrile/water and are usually detected at UV, 280 nm, or with fluorescence. Triglycerides are slightly less nonpolar than fat-soluble vitamins and require 60% acetonitrile/water to run on Ci8. They have poor extinction coefficients, and detection at UV, 220 nm, competes with refractive index detection in sensitivity. A phenyl column run in 50%... 

It is apparent that abnormally increased excretion of kynurenine metabolites after a test dose of tryptophan cannot necessarily be regarded as evidence of vitamin Bg deficiency. This means that the tryptophan load test is unreliable as an index of status in epidemiological studies, although it is (probably) reliable in depletion/repletion studies to determine requirements. 

The main way of determining vitamin K status, and monitoring the efficacy of anticoagulant therapy, is by measuring the time required for the formation of a fibrin clot in citrated blood plasma after the addition of calcium ions and thromboplastin — the prothrombin time. A more sensitive index is provided by direct measurement of preprothrombin in plasma, most commonly by immunoassay using antisera against preprothrombin that do not react with prothrombin. 

The generalities of each vitamin with regard to structure, chemistry, stability, sources, bioavaUability, metabolic functions, deficiency, and requirements are very well detailed in nutrition articles and treatises. Eor this chapter, we have summarized the structure, importance, stability, and sources according to the Merck Index (1989), Basu and Dickerson (1996), Thumham et al. (2000), and Cuellar-Rodriguez (2000). 

A problem arises in the interpretation of leukocyte ascorbate concentrations because of the different capacity of different classes of leukocytes to accumulate the vitamin. Granulocytes are saturated at a concentration of about 530 pmol/10 cells, while mononuclear leukocytes can accumulate 2.5 times more ascorbate. A considerable mythology has developed to the effect that vitamin C requirements are increased in response to infection, inflammation, and trauma, based on reduced leukocyte concentrations of ascorbate in these conditions. However, the fall in leukocyte ascorbate can be accounted for by an increase in the proportion of granulocytes in response to trauma and infection (and hence a fall in the proportion of mononuclear leukocytes). Total leukocyte ascorbate is not a useful index of vitamin C status without a differential white cell count. 

While the tryptophan load test is a useful index of status in controlled depletion/repletion studies to determine vitamin Bg requirements, it is not an appropriate index of status in population studies. 

Some 10-25% of the population have a genetic predisposition to hyperhomocysteinemia, which is a risk factor for atherosclerosis and coronary heart disease, as a result of polymorphisms in the gene for methylenetetrahydrofolate reductase. There is no evidence that supplements of vitamin Bg reduce fasting plasma homocysteine in these subjects, and like the tryptophan load test, the methionine load test may be an appropriate index of status in controlled depletion/repletion studies to determine vitamin Bg requirements, but not in population studies. 

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