Fat Soluble Vitamins
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 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
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:
- B6 (pyridoxine)
- B1 (thiamine)
- B2 (riboflavin)
- B12 (niacin, pantothenic acid, biotin, folic acid and cobalamin)
Vitamin sources, uses and deficiency problems
Vitamin A (fat-soluble)
- Sources: Dairy products, eggs, liver. Can be converted by the body from the beta-carotene found in green vegetables, carrots and liver.
- Uses: Maintains the health of the epithelium and acts on the retina's dark adaptation mechanism.
- Deficiency leads to: Keratinisation of the nasal and respiratory passage epithelium, night blindness
Vitamin B1 (thiamine) (water-soluble)
- Sources: Yeast, egg yolk, liver, wheatgerm, nuts, red meat and cereals
- Uses: Carbohydrate metabolism
- Deficiency leads to: Fatigue, irritability, loss of appetite; severe deficiency can lead to beri-beri
Vitamin B2 (riboflavin) (water-soluble)
- Sources: Dairy products, liver, vegetables, eggs, cereals, fruit, yeast
- Uses: Intracellular metabolism
- Deficiency leads to: Painful tongue and fissures to the corners of the mouth, chapped lips
Vitamin B12 (water-soluble)
- Sources: Liver, red meat, dairy products and fish
- Uses: Essential for manufacturing of genetic material in cells. Involved in the production of erythrocytes
- Deficiency leads to: pernicious anaemia
Vitamin C (ascorbic acid) (water-soluble)
- Sources: Green vegetables and fruit
- Uses: Essential for the maintenance of bones, teeth and gums, ligaments and blood vessels. It is also necessary for ensuring a normal immune response to infection
- Deficiency leads to: Scurvy
Vitamin D (fat-soluble)
- Sources: Fish liver oils, dairy produce. Vitamin D is formed in the skin when it is exposed to sunlight
- Uses: Has a role in the absorption of calcium, which is essential for the maintenance of healthy bones
- Deficiency leads to: Rickets
Vitamin E (fat-soluble)
- Sources: Pure vegetable oils; wheatgerm, wholemeal bread and cereals, egg yoke, nuts sunflower seeds
- Uses: Protects tissues against damage; promotes normal growth and development; helps in normal red blood cell formation
- Deficiency leads to: May cause muscular dystrophy
Vitamin K (fat-soluble)
- Sources: Green vegetables
- Uses: Used by the liver for the formation of prothrombin
- Deficiency leads to: Bleeding due to delayed clotting times caused by lack of clotting factors. Patients may show signs of bruising easily and have nosebleeds.
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).
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, 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.
Vitamin and mineral interactions
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.