vitamins part B 2023 - Tagged.pdf

Vitamins part B Dr Despo Papachristodoulou VITAMIN C (ascorbic acid) Sources Citrus fruits, tomatoes, berries. Function An anti-oxidant nutrient Hydroxylation of proline and lysine in collagen formation. needed to maintain the Fe(II) necessary for proline and lysine hydro...

Vitamins part B Dr Despo Papachristodoulou VITAMIN C (ascorbic acid) Sources Citrus fruits, tomatoes, berries. Function An anti-oxidant nutrient Hydroxylation of proline and lysine in collagen formation. needed to maintain the Fe(II) necessary for proline and lysine hydroxylase activity in the reduced, active state. Reduction of dietary Fe in the stomach for absorption Possibly, in vivo, as an anti-oxidant protecting vitamins A, E, K from oxidation Deficiency Scurvy The well fed human body has a 6 month store of vitamin C Signs of scurvy after three months on vitamin C free diet. impaired wound healing, haemorrhages and anaemia (also from decreased Fe and folate absorption). Vitamin C status in the UK Low status in the elderly, in alcoholics and in adolescents especially on 'junk' food. Smokers need twice the normal intakes (80 mg/day) as the turnover of ascorbic acid is greatly increased by smoking. Megadoses: Benefits uncertain and under review: cholesterol turnover, immune function, male fertility, cancer prevention, Se and Fe utilisation, physical working capacity. supplements may ease symptoms cold: No evidence that megadoses have an effect Heart disease, cancer, eye diseases- no clear pattern Risks of megadoses: Oxalate (major metabolite)) kidney stones in susceptible individuals, diarrhoea, systemic conditioning. Pregnant women on high doses may have infants with unusually high requirements and individuals on high intakes are at risk of deficiency if the intake is lowered to levels which are adequate for most people. FAT SOLUBLE VITAMINS Causes of deficiency Primary: dietary deficiency low fat diet (usually by choice in developed societies) fat malabsorption VITAMIN A Sources as retinol Animal liver and fish liver oils, whole milk and egg yolk plant carotenoids (mainly  carotene) Green/yellow/ orange vegetables and fruit. Absorption Carotenoids are cleaved to 2 retinol molecules conversion is inefficient, ratio carotene : retinol not 1:2 but 6:1 Potency is expressed as retinol equivalents 1 RE = 1 g retinol  Active forms retinoic acid acts as a hormone retinal in vision ( carotene antioxidant) Functions control of protein synthesis retinoic acid binds specific receptor protein in cytosol, then binds chromatin and affects synthesis of proteins involved in cell growth and differentiation. acts in a similar way to steroid hormones. in vision best understood function at low light intensity (scotopic vision) 11-cis retinal participates in conversion of light energy to impulses in the optic nerve in the rod cells of the retina  Transport and Storage From the gut to the liver in chylomicrons From the liver to the tissues bound to a specific retinol binding protein, and pre-albumin. Deficiency rarely seen in developed countries, but common in developing countries e.g. India & SE Asia Usually associated with inadequate protein diets. Affects synthesis of retinol binding protein and therefore transport to the tissues. Administration of vitamin A alone often does not help. Night blindness (role in vision), followed by: progressive keratinisation of the cornea (xerophthalmia), and finally keratomalacia and irreversible blindness. The development of xerophthalmia and keratomalacia relates to its role in the function of epithelial cells and mucopolysaccharide synthesis. Toxicity/Teratogenicity Dermatitis, hair loss, mucous membrane defects, hepatic dysfunction, thinning and fracture of long bones. unlikely with normal sources but possible with supplements e.g. for acne or colds. In pregnancy no more than 3.3mg/day are recommended RNI is 0.7 mg/day for men and 0.6mg/day for women UK animal livers: 13 - 40 mg/100g Pregnant women should not take supplements or eat liver regularly. VITAMIN E Source Vegetable oils especially wheat germ oil, nuts, green vegetables. Canned and frozen foods severely depleted includes family of tocopherols most potent: -tocopherol – naturally occurring ANTIOXIDANT. Safe level - up to 1 g/day  Function Prevents oxidation of unsaturated/poly-unsaturated fatty acids (PUFA) in cell membranes and circulating lipoproteins. PUFA are particularly susceptible to attack by free radicals. Destruction disrupts membrane structure and cell integrity. Some polyunsaturated fatty acids are precursors of prostaglandins and so PG metabolism is also disturbed.  Free radical scavenging Polyunsaturated fatty acids are susceptible to attack by free radicals other radicals are generated in this process. Reaction of a fatty acid radical with oxygen gives a peroxyl radical. This continues chain reaction by attacking other PUFAs it can react with an anti-oxidant – e.g vitamin E - thus terminating the chain reaction  vitamin E becomes a radical itself, stable can be reduced to original form by other antioxidant nutrients, possibly ascorbic acid. Deficiency Known in animals as a cause of sterility and muscular dystrophy.  Human deficiency: Virtually unknown except in premature, low birth weight infants. vitamin E does not cross the placenta easily; human milk is not a good source of vitamin E. Haemolytic anaemia due to fragility of red cell membranes is characteristic. Vitamin E is now included in infant formulae Requirements difficult to establish, likely to be higher with high PUFA intake. A protective effect against cardiovascular disease and cancer? Vitamin E is thought to protect fatty acids and apoprotein B in LDL from oxidative damage. evidence that damaged LDL in arterial wall is part of mechanism that leads to atherosclerotic damage. Studies inconclusive Cancer? May reduce risk in men but not in women. VITAMIN D a group of similar compounds. Cholecalciferol (vitamin D3) occurs naturally in animals. functions by binding to intra-cellular receptors that eventually interact with DNA – i.e. acts like most steroid hormones.  Vitamin D2 (ergocalciferol) derived from ergosterol widely found in plants, fungi and moulds. important pharmaceutically and commercially as a food additive because of ready availability of ergosterol.  Sources: Milk and dairy products, fortified margarine, eggs. Cholecalciferol formed in skin by UV light on 7- dehydrocholesterol, ergocalciferol is formed from ergosterol by the action of UV light, prepared commercially. Function Acts to maintain correct levels of calcium and phosphate in the blood so that proper mineralisation of bone is achieved. Deficiency Rickets in children and osteomalacia in adults Rickets mineral : matrix ratio decreases in bone bending of long bones and kyphosis. Tooth eruption delayed Osteomalacia clinical picture poorly defined. There is muscle weakness, bone pain and decalcification of long bones nearly always due to Vit D deficiency and rarely a calcium deficiency Borderline cases of deficiency common in the UK especially in the elderly and also in Asian children and women especially in the north of England and Scotland Recommendations NHS Consider taking 10 microg between October and March for adults and children over 4 years Toxicity Excessive consumption of vitamin D is toxic. Hypercalcaemia, GI tract disturbances and calcification of soft tissues (heart, lungs, kidney). fatal when severe Intakes of 10 x RNI produce toxicity (100 g). recovery with treatment is rapid. Usually a few weeks VITAMIN K Sources Green leafy vegetables best, small amounts in milk, meat, eggs and cereals A considerable amount from the bacterial flora of the jejunum and ileum. Human milk has a low vitamin-K content infants may have marginal insufficiency it does not cross the placenta efficiently the neonatal gut is sterile. Deficiency Blood clotting is defective. This process depends on a cascade system of interacting proteins. Deficiency resulting in increased blood clotting time is rare except: In long term antibiotic therapy When should one limit the intake of vit K? anticoagulation therapy Warfarin Vit K rich foods should be avoided as they promote blood clotting haemorrhagic disease of the new-born poor placental transfer and no gut flora. Some affected babies develop intracranial haemorrhages. Of these, 50% die and the other 50% tend to have neurological malfunction. In the UK babies have been given vitamin K at birth since the 1950s.  Message from DP You are not expected to know requirements (RNI) except perhaps for vitamin C.