Micronutrients and Vitamins

• Vitamins are classified based on their solubility.
• Vitamins have general characteristics such as sources, recommended daily allowance (RDA), chemical structure, digestion & absorption, transport in blood, storage & excretion, function, metabolic effects, toxicity, deficiency states.
• Many vitamins and trace metals are essential nutrients.
• Deficiencies of micronutrients lead to specific clinical syndromes.
• Vitamins are closely linked to malabsorption syndromes and also occur as a complication of gastrointestinal tract surgery.
• Multiple micronutrient deficiencies are much more common than single deficiencies.
• Nutritional deficiencies of individual vitamins and minerals cause distinctive deficiency states.
• The metabolic functions of the missing nutrient are related to the deficiency state.
• Vitamin C deficiency (scurvy) causes connective tissue problems because of impaired collagen synthesis.
• Iron deficiency causes anemia because of impaired hemoglobin synthesis.
• Although the incidence of severe nutritional deficiencies has declined in affluent countries, vitamin and mineral nutrition is still a major public health concern for at-risk groups, including infants, pregnant women, alcoholics, and the elderly.
• Malnutrition is usually associated with multiple nutrient deficiencies.
• The assessment of micronutrient status is difficult for several reasons.
• Measurements of concentrations of circulating vitamins are inappropriate in the case of water-soluble vitamins, because these levels relate to the recent intake and do not reflect overall body status.
• Measurement of activities of enzymes associated with particular vitamins is the most appropriate assessment.
• Most water-soluble vitamins are precursors of coenzymes.
• For evaluation of trace element toxicity, tissues other than blood may need to be analyzed before a diagnosis of metal poisoning can be made.
• Fat-soluble vitamins are more likely to accumulate in the body and cause toxicity, especially vitamin A and vitamin D can be toxic in excess.
• A decrease in level of a nutrient within blood or plasma does not necessarily indicate a deficiency; it could be simply reflecting a metabolic response to stress or a change in physiologic status, such as pregnancy.
• The circulating concentrations of trace metals bear little relation to nutrient status.
• Water-soluble vitamins are readily absorbed, but the absorption of fat-soluble vitamins depends on mixed bile salt micelles.
• All water-soluble vitamins are B vitamins except Vitamin C.
• Deficiencies of fat-soluble vitamins are most likely to occur in patients with fat malabsorption.
• Renal excretion of excess water-soluble vitamins is unproblematic, but fat-soluble vitamins must be metabolized to water-soluble products before they can be excreted.
• There are also problems with interpretation of circulating concentrations of fat-soluble vitamins.
• The fat-soluble vitamins are antioxidants or precursors of hormone-like substances.
• Supplements of these vitamins are most effective when they are taken with a fatty meal.
• Most water-soluble vitamins are transported in the blood as such, but fat-soluble vitamins are transported either as constituents of lipoproteins or bound to specific plasma proteins.
• This is usually carried out as stimulation tests, i.e. enzyme activity is measured in the absence and in the presence of the vitamin.
• A deficit is recognized if the enzyme activity is stimulated in the presence of added vitamin.
• Folic acid consists of pteroic acid (pteridine + para-aminobenzoic acid [PABA]) and one to seven γ-linked Glutamate residues.
• Avidin, found in egg whites, is a 68 kDa glycoprotein that binds biotin with a Kd = 10 - 15 M.
• Absorption of Vitamin B12 is complex and requires intrinsic factor.
• Vitamin B12 is produced by microorganisms but not by plants, and is found in animal products such as meat, eggs, dairy, and seafood.
• Vitamin B12 is required by methylmalonyl CoA mutase and methionine synthetase.
• Cobalamin is a complex tetrapyrrole structure that contains cobalt ion, similar to heme, called a corrin.
• Cobalamin, also known as Vitamin B12, is the largest B vitamin and is a part of the structure of heme.
• Deficiencies in Vitamin B12 are rare and associated with anemia.
• Vitamin B12 is involved in the transfer of methyl groups.
• Fat-soluble vitamins are associated with body fat and are often stored in tissues with circulating concentrations being kept relatively constant.