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 are unable to make vitamins.
There are thirteen vitamins 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. Any disease or disorder that affects the absorption of fat, such as coeliac disease, could lead to a deficiency of these vitamins. Once absorbed into the circulation these vitamins are carried to the liver where they are stored.
Vitamins A, D, E and K make up the 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, such as Vitamin C and the B vitamins are stored in the body for only a brief period of time and are then excreted by the kidneys. The one exception to this is vitamin B12, which is stored in the liver. Water-soluble vitamins need to be taken daily.
Vitamin C (ascorbic acid) and the B complex group make up the nine water soluble vitamins. The B complex group comprises of vitamins:
Vitamins contain no useful energy for the body but they do link and regulate the sequence of metabolic reactions that release energy within 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 level of physical activity.
The recommended daily requirements (RDR or RDA) for men, women are shown in the Table below. These requirements should be easily met if a balanced diet is adhered to; however, there are groups that may be at greater risk of developing vitamin deficiencies than others. These include those on restricted diets, patients who have digestive disorders that affect the absorption of fat, patients on lipid-lowering medication and those whose dietary choices are affected by financial or for conscientious reasons (Trounce and Gould, 1997). For these groups there may be advantages in taking a general or specific vitamin supplement following advice from a doctor or nutritionist. However, for those on a balanced diet there is little to be gained from taking additional vitamins (NHS Direct Online, 2003).
The above table is the recommended dietary allowance revised 1989. Food and Nutrition Board, National Academy of Sciences-National Research Council, Washington DC, USA
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, diarrhea 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% of oxygen containing free radicals like superoxide, hydrogen peroxide and hydroxyl. The body's level of pentane can be used to monitor the amount 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 if supplements can be beneficial in combating free radicals then vitamin E may be the most effective.
Many vitamins and minerals interact, working alongside each other 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 deficiency in zinc.