Vitamins
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
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
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:
- B6 (pyridoxine).
- B1 (thiamine).
- B2 (riboflavin).
- B12 (niacin, pantothenic acid, biotin, folic acid and cobalamin).
Vitamin sources, use and deficiency problems
Vitamin A (fat-soluble)
- Sources: Dairy products, eggs, and liver can be converted by the body from the beta-carotene found in green vegetables, carrots and liver.
- Uses: Maintain the epithelium's health and act on the retina's dark adaptation mechanism.
- Deficiency leads to Keratinisation of the nasal and respiratory passage epithelium and night blindness.
Vitamin B1 (thiamine) (water-soluble)
- Sources: Yeast, egg yolk, liver, wheat germ, nuts, red meat and cereals.
- Uses: Carbohydrate metabolism.
- Deficiency leads to fatigue, irritability, and loss of appetite; severe deficiency can lead to beriberi.
Vitamin B2 (riboflavin) (water-soluble)
- Sources: Dairy products, liver, vegetables, eggs, cereals, fruit, yeast.
- Uses: Intracellular metabolism.
- Deficiency leads to a painful tongue and fissures to the corners of the mouth and chapped lips.
Vitamin B12 (water-soluble)
- Sources: Liver, red meat, dairy products and fish.
- Uses: Essential for manufacturing 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 maintaining bones, teeth and gums, ligaments and blood vessels. It is also necessary for ensuring a healthy 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 yolk, nuts, sunflower seeds.
- Uses: Protects tissues against damage; promotes normal growth and development; helps in normal red blood cell formation.
- Deficiency leads to 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 a lack of clotting factors. Patients may show signs of bruising easily and have nosebleeds.
Daily Requirements
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)[1]. 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.
| Vitamin | Men | Women | Sources |
| A | 0.7mg | 0.6mg | cheese, eggs, oily fish, such as mackerel, milk, fortified low-fat spreads, yoghurt. |
| B6 | 1.4mg | 1.2mg | pork, chicken, turkey, cod, bread, whole cereals such as oatmeal, wheat germ and rice, eggs, vegetables, soya beans, peanuts, milk, potatoes, and some fortified breakfast cereals. |
| B12 | 0.0015mg | 0.0015mg | meat, salmon, cod, milk, cheese, eggs, yeast extract, some fortified breakfast cereals. |
| B3 (niacin) | 17mg | 13mg | meat, fish, wheat flour, maize flour, eggs, milk. |
| Pantothenic Acid | 200mg | 200mg | chicken, beef, potatoes, porridge, tomatoes, kidney, eggs, broccoli, and whole grains, such as brown rice and wholemeal bread. |
| B2 (riboflavin) | 1.3mg | 1.1mg | milk, eggs, fortified breakfast cereals, rice, mushrooms. |
| B1 (thiamin) | 1mg | 0.8mg | pork, vegetables, milk, cheese, peas, fresh and dried fruit, eggs, wholegrain bread. |
| Folic Acid | 0.2mg | 0.2mg | broccoli, brussels sprouts, asparagus, peas, chickpeas, brown rice. |
| C | 40mg | 40mg | peppers, broccoli, brussels sprouts, sweet potatoes, oranges, kiwi fruit. |
| D | 0.025mg | 0.025mg | oily fish, such as salmon and sardines, eggs, fortified fat spreads, fortified breakfast cereals, powdered milk. |
| E | 4mg | 3mg | nuts and seeds, wheat germ found in cereals and cereal products. |
| K | 0.001mg | 0.001mg | green leafy vegetables such as broccoli and spinach, vegetable oils, cereals. |
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, 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 be voided in the urine.
Free Radicals
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.
References
- NHS Direct Online (2014) Vitamins and Minerals [WWW] Available from https://www.nhs.uk/Conditions/vitamins-minerals/Pages/vitamins-minerals.aspx [Accessed 20/11/2014]
Page Reference
If you quote information from this page in your work, then the reference for this page is:
- MACKENZIE, B. (2001) Vitamins [WWW] Available from: https://www.brianmac.co.uk/vitamins.htm [Accessed