| Vitamins and trace metals are an important part of nutrition and many of them are essential nutrients. Deficiencies of micronutrients lead to specific clinical syndromes. They accompany general malnutrition or become manifested during illness. They also may occur as a result of surgical procedures on the gastrointestinal tract. Importantly, multiple deficiencies of micronutrients are much more common than single deficiencies. This chapter should be read in conjunction with Chapter 21.
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| Vitamins are an inherent part of functional protein molecules. They act as coenzymes in the specific reactions, e.g. riboflavin in oxidoreductase reactions or biotin in carboxylation reactions. There are fat-soluble and water-soluble vitamins. Fat-soluble vitamins are vitamins A, D, E, and K, and water-soluble are vitamins B1, B2, B3, B5, B6, B12, folate, biotin and C.
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| Several trace metals are also essential nutrients
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Many of the trace metals function as part of protein molecules or metalloenzymes. Such proteins, without their trace metal prosthetic groups, e.g. Zn, Mn, or Mg, lose their biological function. Some trace elements are cytotoxic. In addition to the essential trace elements, other trace metals (e.g. cadmium, mercury, and aluminium) find their way into the food chain and can be toxic to cells. The toxic metals also include essential trace elements when taken in large amounts, e.g. copper and manganese . The essential requirements for these metals in the prevention of disease and their association with certain pathologies only came to light when suitable analytical methods such atomic absorption spectrometry and mass spectrometry were developed.
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| To prevent the development of pathologies caused by vitamin or trace metal deficiencies, certain levels of intake have been recommended for healthy people. The requirement for vitamins depends, to some extent, on the macronutrient intake (Chapter 21). Although single deficiency states may occur, poor diets are often characterized by multiple nutrient deficiencies. Specific vitamin-associated pathologies are also well recognized.
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| Malnutrition is usually associated with multiple nutrient deficiencies
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| Assessment of nutrient status is fraught with difficulties since malnutrition is usually associated with multiple nutrient deficiencies, each one having functional implications, and all being interrelated. Micronutrient assessment is even more difficult in situations where subclinical deficits exist. Measurements of circulating vitamin levels are inappropriate in the case of water-soluble vitamins, because these levels relate to the recent intake and do not reflect overall vitamin status. Therefore, measurement of enzyme function associated with particular water-soluble vitamins has been suggested as the most appropriate way to assess micronutrient status. This is usually carried out as stimulation tests, i.e., enzyme activity is measured in the absence and then in the presence of the vitamin as reagent. Deficit is recognized if there is a stimulation of enzyme activity in the presence of added vitamins.
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| There are also potential problems with interpretation of circulating concentrations of fat-soluble vitamins. These vitamins are associated with body fat and are often stored in specific tissues with circulating concentrations kept relatively constant; for example, vitamin A is stored in the liver and transported by specific binding proteins in the plasma. Furthermore, a decrease in level of a nutrient within blood or plasma does not need to indicate a deficiency or an increased requirement: it could be simply reflecting a metabolic adjustment to stress or a change in physiologic status, such as pregnancy. Similar principles apply to trace metals, where the circulating levels bear little relation to nutrient status. For evaluation of trace element toxicity, tissues other than blood may need to be analyzed before a definite diagnosis of metal poisoning can be made.
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