Vitamins: Their Role in the Human Body
George F. M. Ball
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This single-source reference draws together the current knowledge of the vitamins' biological properties in the context of human nutrition. Vitamins are co-enzymes, antioxidants or precursors of hormones and are therefore involved in a great many biochemical and physiological processes. They play a vital role in the maintenance of health, and there is evidence that dietary sources of vitamins have beneficial effects in the prevention of heart-related diseases, bone diseases and possibly cancer.
Following introductory chapters on historical and nutritional aspects of vitamins, the next four chapters cover relevant and detailed aspects of physiology and functional anatomy, biochemistry, immunology and the regulation of protein synthesis by nuclear hormone receptors. These background chapters, supported by a glossary of terms, provide the scientific principles upon which vitamin functions are based. The following thirteen chapters deal with each vitamin in turn. Subject areas include chemical structure, intestinal absorption, transport, metabolism, biochemical and physiological actions, immunoregulatory properties, deficiency-related diseases and potential toxicity. An extensive bibliography refers the reader to the original research literature.
Vitamins is aimed at nutritionists, biochemists, physiologists and physicians whether they be researchers, teachers or students. Food scientists, food technologists and many others working in the health professions will also find much of use and interest in the book. The inclusion of the theoretical principles in the background chapters makes the book an ideal starting point for those working outside the area who need a solid overview of the subject.
other double bonds forms β-apocarotenals (e.g. 8´-CHO), which can be shortened to retinaldehyde. β-Apocarotenals may be oxidized to β-apocarotenoic acids (e.g. 8´-COOH), which can form retinoic acid. Retinol is esterified, incorporated in chylomicrons together with some intact β-carotene, and secreted into lymph. Retinoic acid enters portal blood accompanied by other polar metabolites. Reprinted from Biochimica et Biophysica Acta, Vol. 486, Sharma et al., Studies on the metabolism of β-carotene
which was positively correlated with the size of the plasma retinol pool; i.e. the lower the plasma retinol concentration, the lower the vitamin A utilization rate. The increased rate of utilization observed in rats of higher vitamin A status was reflected in an increased rate of retinol catabolism. It appeared that some minimal utilization rate is maintained as long as dietary supply and/or liver stores of vitamin A can maintain normal plasma retinol concentrations. The decreased utilization
and γ. The receptors show characteristic patterns of distribution in adult and embryonic tissues (Table 7.2). The three RAR subtypes within a given animal 06/07/04, 14:07:00 156 Vitamins: their role in the human body Table 7.2 Distribution of RAR and RXR in mammalian adult and embryonic tissues. Receptor Adult Developing embryo RARα Ubiquitous Ubiquitous RARβ Kidney, adrenal glands, pituitary gland, prostate gland, spinal cord, brain, muscle, bone Neural crest cells Developing
lysolipids and oxidatively modified low density lipoprotein on endothelium-dependent relaxation of rabbit aorta. Circulation Research, 72, 161–6. Marcus, A. J. (1978) The role of lipids in platelet function: with particular reference to the arachidonic acid pathway. Journal of Lipid Research, 19, 793–826. Meydani, M. (1998) Nutrition, immune cells, and atherosclerosis. Nutrition Reviews, 56, S177–82. Minor, R. L. Jr., Myers, P. R., Guerra, R. Jr., Bates, J. N. & Harrison, D. G. (1990)
Cyclic GMP, in the presence of calcium, mediates the discharge of lysosomal enzymes, whereas cyclic AMP inhibits the discharge. Many cellular functions are similarly regulated by the opposing effects of these two cyclic nucleotides. Cellular concentrations of cyclic GMP and cyclic AMP, and thus cellular functions, can be influenced by hormones and neurotransmitters. For example, acetylcholine promotes the accumulation of cyclic GMP and thus enhances lysosomal enzyme discharge, while adrenaline