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 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 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, brussel 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 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.

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