Water-soluble vitamins Vitamin deficiencies Metabolism General Diseases etc. A deficiency of biotin, commonly seen in alcoholics, can cause neurological symptoms Levels of folate are particularly low in the elderly Deficiency of folate and cobalamin can lead to macrocytic anaemia Cysteine accumulates in people with low vitamin B12 (cobalamin) status Ascorbic acid (vitamin C) is so-called because of its ability to prevent scurvy Niacin is the only water-soluble vitamin that can be formed in humans from an essential dietary amino acid Niacin is required for carboxylation reactions in the body Biotin plays a key role in gluconeogenesis and fatty acid synthesis Certain water-soluble vitamin(s) play a role in control of gene expression, via methylation of cytosine in DNA Certain water-soluble vitamin(s) play a role in control of gene expression, via demethylation of DNA and histones Biosynthesis of urea and of homocysteine both depend on transmethylation reactions Corn (maize) is a potentially good source of niacin, but the vitamin is tightly bound and is released by soaking in weak alkali A typical healthy diet with 5 helpings of fruit and vegetables per day will provide about 40 mg of vitamin C Limey is a North American slang nickname for Britons, based on the practice in the Royal Navy to provide sailors with lime juice in addition to their daily watered-down rum ration Nutritionists monitoring patients undergoing bariatric surgery should pay special attention to levels of vitamins B1 and B12 (thiamine and cobalamin) Plasma total homocysteine levels are often very low in patients with dementia Folate deficiency can lead to cardiovascular disease There is evidence of an increased risk of cancer associated with mandatory folic acid fortification of foodstuffs
Minerals and trace elements Iodine Zinc Magnesium Copper Most of the iodine taken in by the average Norwegian adult comes from fish Meat is a good source of iodine Iodine deficiency affects people living in low-lying regions of Asia where flooding depletes the soil The recommended daily intake of iodine is 150 micrograms for adults, but children need more than this to avoid cretinism A long period of reduced iodine intake is required before signs of iodine deficiency will appear Most of the zinc in the body is in skeletal muscle and bone A deficiency of zinc during embryogenesis can cause birth defects Zinc competes with iron for uptake by metallothioneins in the intestine Recognition of the DNA target is the function of zinc fingers in transcription factors Phytate is a hexose sugar found in whole-grain bread, that binds zinc and inhibits uptake Meat is a good source of zinc in the average diet Magnesium is not a trace element A high concentration of magnesium is found in the nucleus Although magnesium is a co-factor in many enzymic reactions, it binds weakly to active sites Vegetables are a poor source of magnesium Eating clay (geophagy) is a sign of magnesium deficiency Anorexia can be caused by magnesium deficiency A vegetarian diet is likely to be deficient in copper Copper is transported to the liver and there incorporated into ceruloplasmin Excessive intake of copper can lead to anaemia Copper deficiency can lead to anaemia Cu/Zn superoxide dismutase (SOD) is an antioxidant enzyme found mainly in the brain The gene for Cu/Zn SOD is located on chromosome 21 and people with Down s syndrome have high levels of the enzyme
Selenium Selenium can replace sulphur in the amino acids cysteine and methionine Population studies have shown an association of low selenium levels with increased cancer risk Selenium is incorporated into glutathione peroxidase by replacing the sulphur of cysteine and methionine residues in the molecule post-translationally Selenium is more toxic than arsenic Blood selenium levels in Norwegians are high, because of high levels in Norwegian wheat
Iron Transport, absorption etc. Dietary iron Diseases Haem and non-haem iron are absorbed with similar efficiency in the gut Ferritin is the major transport molecule for iron The ferritin complex can contain thousands of iron atoms Iron from haem is absorbed to a greater extent than non-haem iron The transferrin molecule can bind many Fe +++ ions TIBC (total iron-binding capacity) is an indirect measure of transferrin Iron is actively excreted through the kidneys Haem-iron inhibits the uptake of non-haem iron Most non-haem iron in the diet comes from cereals Brunost (Norwegian brown whey cheese) is fortified with iron Almost half of the iron in meat or fish is in the form of haem The recommended iron intake in Norway is 15 mg for (pre-menopausal) women and 9 mg for men Many symptoms of haemochromatosis and iron-deficiency anaemia are similar Fatigue and headaches are common symptoms of anaemia Iron-deficiency anaemia is more common in industrialised than in developing countries Haemochromatosis is an X-linked genetic condition and therefore more common in females Symptoms of haemochromatosis are treated by regular blood-letting Chronic iron overload can lead to diabetes type 2
Vitamin A (22) Vitamin A and vision 11-cis-retinol forms rhodopsin in the cells of the retina The development of cataracts is slowed by vitamin A supplementation Night blindness can be an indication of vitamin A deficiency Xerophthalmia is a childhood blinding disease caused by lack of vitamin A in the diet Which of the following are pro-vitamin A carotenoids? Lutein Lycopene Retinol Beta-carotene Beta-cryptoxanthine Zeaxanthine Transport and metabolism Retinol is transported in plasma bound to albumin Cyp26 is an enzyme that oxidises all-trans retinol into all-trans retinal Transthyretin is a carrier of both thyroxine and retinol bound to retinol-binding protein LRAT is the enzyme that metabolises retinol to retinoic acid Vitamin A deficiency may be due to Eating disorders Diabetes type 2 Excessive consumption of alcohol Low intake of animal products Good sources of vitamin A are Red meat Butter Whole grain foods Spinach
Vitamin D. vitamin K, Calcium (14) Dietary sources Vitamin K Peanuts are a good source of vitamin K Vitamin D in the Norwegian diet comes mainly from poultry and eggs Menaquinone inhibits apoptosis of osteoblasts and enhances apoptosis of osteoclasts Vitamin K is absorbed from the gut and distributed to tissues in association with chylomicrons Vitamin D and vitamin D receptor (VDR) Calcium Diseases Vitamin D acts mainly through PTH and increases bone mass The nuclear receptor VDR interacts directly with RNA polymerase II Activated VDR and the vitamin A receptor form dimers together VDR both downregulates and upregulates its target genes The recommended daily calcium intake for men and women in Norway is 800 mg Calcitonin decreases the concentration of calcium in blood Low calcium intake from food causes hypocalcaemia in children Calcium excess from supplements can increase the risk of myocardial infarction Rickets is caused by a deficiency of vitamin K in the diet of children Supplementation with calcium and vitamin D together may reduce bone loss in patients treated with corticosteroids for rheumatoid arthritis
Vitamin E, oxidative stress and antioxidants (12) Oxidative stress Antioxidants The Fenton reaction, catalysed by transition metals, protects against reactive oxygen Superoxide is a reactive form of oxygen with an unpaired electron and is therefore a free radical Hydrogen peroxide is a by-product of normal respiration in the mitochondria Malondialdehyde measured in the urine is a marker of lipid oxidation Oxidised lipids are taken up by lymphocytes and deposited in arterial plaques The intrinsic antioxidant enzyme catalase converts superoxide to hydrogen peroxide The antioxidant glutathione also takes part in phase II biotransformation reactions as a carrier for xenobiotics destined for excretion Vitamin E Alpha-tocopherol is the major form of vitamin E in the diet Vitamin E deficiency is very rare in humans but can occur as a consequence of fat malabsorption syndromes Vitamin E is involved in cell signalling and regulates expression of certain genes Alpha-tocopherol catalyses the regeneration of glutathione (GSH) from the reduced form (GSSG) Plant seeds and vegetable oils are good sources of vitamin E