Vitamins (1).pdf

Vitamins (1) Pr. Roberta FORESTI Professor of Biochemistry, Faculty of Health, UPEC [email protected]  What are vitamins? Vitamins are substances which have no energy value but which are vit...

Vitamins (1) Pr. Roberta FORESTI Professor of Biochemistry, Faculty of Health, UPEC [email protected]  What are vitamins? Vitamins are substances which have no energy value but which are vital for the body since they are needed for many physiological processes. Apart from vitamins K and D, the human body cannot synthetise vitamins. Because of this we need to get vitamins though our diet so that our bodies can function correctly. Vitamin (vita=life in Latin) Fat-soluble (liposoluble) vitamins Water-soluble (hydrosoluble) vitamins Vitamin A - Retinoids and carotenoids Vitamin B1 - Thiamin Vitamin D Vitamin B2 - Riboflavin Vitamin E - Tocopherols Vitamin B3 - Niacin Vitamin K Vitamin B5 - Pantothenic acid Vitamin B6 - Pyridoxine Vitamin B8 - Biotin Vitamin B9 - Folate or Folic acid Vitamin B12 Vitamin C - Ascorbic acid  Fat-soluble vitamins are stored in adipose tissue (vitamins D and E) and to a significant degree in the liver (vitamin A). The fact that they can build up in the organism means there is a potential risk of toxicity if intake is too high. Water-soluble vitamins can also be stored by the body, but there is less of a risk of overdosing as they are eliminated through the urine. Vitamin A – Retinoids and Carotenoids Fat-soluble Vitamin A is probably the most important vitamin in human nutrition. Retinol is the main precursor of vitamin A (see below for chemical forms of vitamin A). Carotenoids, especially β- carotene, is also converted into vitamin A. They both contribute to the total vitamin A intake. Vitamin A is essential at all stages of life. Its key role in the mechanism of eyesight is now clearly established. It also plays a part in the regulation (activation, repression) of gene expression, and is thus involved in a number of bodily functions: development of the embryo, cell growth, tissue renewal (skin, intestinal mucosa), immune system, etc. In addition to the properties of vitamin A, ß-carotene can act as an antioxidant (free-radical scavenger). Vitamin A is directly involved in vision because it is a light-sensitive pigment in the rhodopsins and iodopsins, which are present in the retina of the eye. Recommended intakes RE: retinol equivalent (retinol + β-carotene)  Main dietary sources of vitamin A Vitamin A is present in the form of retinol Vitamin A in the form of provitamin carotenoids and its derivatives exclusively in products of is mainly found in products of plant origin animal origin. Retinol containing foods Pro-vitamin A containing foods Liver Sweet potato Kidney Carrots Oily fish Peppers Full fat dairy products Pumpkin Dark green vegetables (spinach, cabbage) Egg yolk (orange color is carotenoids) We need fats to absorb vitamin A!  Vitamin A deficiency disease Vitamin A deficiency (Xerophthalmia) is a major global cause of blindness in children under 5 in the developing world (they do not have stores of vitamin A). It is the most common preventable cause of blindness. Vitamin A deficiency does not seem to exist in industrialised countries. Night blindness (early stage) Xerosis of the cornea and conjunctiva (dry, hazy appearance) Irreversible blindness if deficiency is not addressed Impaired immunity leading to increased childhood mortality (increased susceptibility to infection in children and vulnerable groups like the elderly). Diversification of the diet How can we prevent it? Improved hygiene Periodic (every 6 months) oral supplements with vitamin A in children under 5 in endemic areas  Vitamin A toxicity Vitamin A toxicity can be acute and chronic. A single dose of > 300 mg in adults causes nausea, vomiting and headache. Prolonged and regular consumption of 7.5-9 mg/day in adults causes toxicity to the sin, central nervous system and, liver and bones. High intake of retinol during pregnancy is deleterious (especially 1st trimester), it cause birth defects. As a precaution pregnant women are recommended to avoid liver, which is a very rich source of vitamin A. Carotenoids do not seem to cause toxicity (but at very high intakes the skin, plasma and fat can become very orange). However, two important clinical trials have shown that in smokers, supplementation with β-carotene increases the risk of lung cancer! Vitamin A toxicity Vitamin D Fat-soluble Vitamin D is not strictly a vitamin but is a ‘steroid hormone’ that is involved in calcium homeostasis and the regulation of cell proliferation and differentiation. In addition, it modulates the response of the immune system. When calcium levels are normal, vitamin D promotes the growth of bones by increasing calcium absorption. Thus, vitamin D has a key role in bone health. Vitamin D enters bone cells precursors (osteocytes and osteoblasts) and stimulates differentiation into osteoclasts (mature bone cells). Although there are some dietary sources of vitamin D, they are non important because the major production of the vitamin occurs in the human body following exposure to sunlight. Active form of vitamin D  How much exposure to the sun? By exposing the skin to the sun for 15 to 20 minutes in late morning or in the afternoon, we ensure that our body has an adequate daily intake of vitamin D. This is true for Northern Europe, UK, USA, Canada. It is latitude dependent and seasonal dependent (from April to September vitamin D is produced). If you live in the Caribbean, vitamin D is produced all year. Since vitamin D is fat soluble we should on a normal summer produce enough for winter months. The distribution of serum 25(OH)D in winter and in summer. Recommended intakes  Dietary sources of vitamin D Oily fish, such as herring, sardines, salmon and mackerel Dairy products fortified with vitamin D Egg yolk Breakfast cereals fortified with vitamin D Butter and margarine Offal (particularly liver) Diet is not a good source of vitamin D!  Vitamin D deficiency disease Clinical symptoms of vitamin D deficiency manifest as rickets in children and osteomalacia in adults. Without vitamin D we do not calcify and cause the differentiation into osteoclasts, cartilage keeps growing and bowing legs form. Rickets symptoms Osteomalacia symptoms (less pronounced than in children) Skeletal changes with deformities and growth retardation Diffuse pain in bone Bone pain and tenderness Specific fractures Enlarged epiphyses (at growing ends of Muscle pain and weakness bones) Roth et al, Ann, N, Y, Acad. Sci. 2018 Vitamin E – Tocopherols Fat-soluble Vitamin E is a lipid-soluble antioxidant in the cell membrane. It is a combination of 8 vitamers: the tocopherols and tocotrienols. They all have varying antioxidant activity and in the cell membrane they cooperate with vitamin C in fighting lipid peroxidation (oxidative damage to the lipids of the membrane). Vitamin E has also effects in the immune response and has anti-inflammatory effects.  Antioxidant activity of vitamin E in the membrane The cell membrane contains polyunsaturated fatty acids (PUFA) that are susceptible to free radical mediated lipid peroxidation (LPO). Vitamin E does not prevent radical formation, or the initial oxidation of fatty acids, but terminates the LPO chain reaction. It donates a hydrogen atom from its hydroxyl group to the free radical. It cooperates with vitamin C in protecting the membrane Recommended intakes  Dietary sources of vitamin E Fats and oils (sunflower oil, olive oil) Oily fish Nuts Seeds Beans wholegrain cereals (wheat germ is especially rich)  Signs of vitamin E deficiency Vitamin E deficiency is difficult to find in humans and we mostly have information from animal studies, where the general signs are damage to the cell membrane. A clinical vitamin E deficiency causes neurological symptoms including ataxia. It can be observed in patients with cholestatic liver disease, severe undernutrition, lipid absorption disorders and cystic fibrosis-diseases where there is an abnormality in fat metabolism. There is an inverse association between plasma vitamin E concentrations and mortality from cancer and heart disease. It appears that the correlation is for dietary pattern and vitamin E rather than supplements; Vitamin K Fat-soluble Vitamin K encompasses phylloquinone (vitamin K1), menaquinones (vitamin K2) and synthetic menadione (vitamin K3). Vitamin K is involved in the activation of proteins that play a role in blood clotting (vitamin K1) and bone metabolism (vitamin K2). The biological activity of vitamin K is dependent on its ability to switch between oxidized (quinone and epoxide) and reduced form (quinol) in the vitamin K cycle. The conversion of quinol to epoxide leads to the formation of carboxyglutamate (gla) residues on proteins. The proteins formed are known as gla-proteins or vitamin K-dependent proteins. They have the ability to bind to calcium, which is linked to their biological activity. Coagulation factors II, VII, IX and X are all gla- proteins. Osteocalcin is the main gla-protein in mineralized bone. Recommended intakes  Dietary sources of vitamin K Vitamin K1 (phylloquinone) is found in plants. Vitamin K2 (menaquinone) is synthesized by bacteria and found in some animal products. Vitamin K1 containing foods Vitamin K2 containing foods Herbs (parsley) Liver Kale Beef Spinach and salads Poultry Cruciferous vegetables (broccoli, Egg yolk cauliflower etc.) Fermented products Soybean and rapeseed oils However, little is known about the types and content of menaquinones in food and it is unclear how much menaquinone derived from intestinal bacteria contributes to vitamin K nutrition.  Vitamin K deficiency Vitamin K deficiency results in prolonged prothrombin time (increased blood clotting time) and hemorrhagic disease because of an impaired synthesis of the vitamin K dependent blood clotting proteins. Osteoporosis could also be an evidence of lower vitamin K status. Hemorrhagic disease of the new born is characterized by inadequate plasma vitamin K levels in some breast-fed babies due to poor maternal nutrition, intestinal malabsorption or inadequate placental transfer. They exhibit spontaneous bruising or bleeding (in severe cases intracranial hemorrhage-fatal). Recommended oral dose of vitamin K at birth or daily dose to the mother.