Vitamins serve crucial functions in almost all bodily processes (immune, hormonal and nervous systems) and must be obtained from food or supplements as our bodies cannot make vitamins. Thirteen vitamins are classified as either water-soluble (C and B complex) or fat-soluble (A, D, E and K).
Fat-soluble vitamins are absorbed, together with fat from the intestine, into the circulation. Once absorbed into the circulation, these vitamins are carried to the liver, where they are stored. Any disease or disorder that affects the absorption of fat, such as coeliac disease, could lead to a deficiency of these vitamins.
Vitamins A, D, E and K make up the fat-soluble vitamins. Vitamins A, D and K are stored in the liver, and vitamin E is distributed throughout the body's fatty tissues.
Water-soluble vitamins need to be taken daily. Water-soluble vitamins, such as Vitamin C and B, are stored in the body for only a brief period and then excreted by the kidneys. The one exception to this is vitamin B12, held in the liver.
Vitamin C (ascorbic acid) and the B complex group comprise the nine water-soluble vitamins. The B complex group includes vitamins:
Vitamin sources, use and deficiency problems
Vitamin A (fat-soluble)
Vitamin B1 (thiamine) (water-soluble)
Vitamin B2 (riboflavin) (water-soluble)
Vitamin B12 (water-soluble)
Vitamin C (ascorbic acid) (water-soluble)
Vitamin D (fat-soluble)
Vitamin E (fat-soluble)
Vitamin K (fat-soluble)
Vitamins contain no valuable energy for the body but link and regulate the sequence of metabolic reactions that release energy from the food we consume. Vitamins cannot be made in the body and must be obtained in our diet. A well-balanced diet provides an adequate quantity of all vitamins regardless of age and physical activity level.
The recommended daily requirements of vitamins for men and women are shown in the Table below (NHS Direct Online 2007). These requirements should be easily met if a balanced diet is adhered to. Some groups may be at higher risk of developing vitamin deficiencies than others, e.g. those on restricted diets, patients with digestive disorders that affect the absorption of fat and patients on lipid-lowering medication. There may be advantages in taking a general or specific vitamin supplement following advice from a doctor or nutritionist for these groups.
Toxicity of Vitamins
Fat-soluble vitamins should not be consumed in excess as they are stored in the body, and an excess can result in side effects. An excess of vitamin A may result in irritability, weight loss, dry itchy skin in children and nausea, headache, and diarrhoea in adults.
An excess of water-soluble vitamins should not result in any side effects as they will disperse in the body fluids and voided in the urine.
Electron leakage in the electron transport system results in approximately 2 to 5% oxygen-containing free radicals like superoxide, hydrogen peroxide and hydroxyl. The body's level of pentane can be used to monitor the number of free radicals.
Exercise increases the production of free radicals, and a build-up of free radicals increases the potential for cellular damage to many biological substances. Research indicates that the body's natural defences of a well-nourished athlete are adequate in response to increased amounts of free radicals.
Available research indicates that vitamin E may be the most effective if supplements can be beneficial in combating free radicals.
Vitamin and mineral interactions
Many vitamins and minerals interact, working together in groups, e.g. a good balance of vitamin D, calcium, phosphorus, magnesium, zinc, fluoride, chloride, manganese, copper and sulphur is required for healthy bones.
Many of them can enhance or impair another vitamin or mineral's absorption and functioning, e.g. an excessive amount of iron can cause a zinc deficiency.
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