Guide to Vitamins

Vitamins are organic chemicals that the body needs in order to function correctly. Vitamins do not have any energy value (or calories) themselves. However, they perform essential functions in the body such as:

• breaking down fat, carbohydrate and protein
• repairing body tissues
• helping the immune system
• preventing diseases and birth defects.

Vitamins are derived from plants or animals, ie living things, unlike minerals. Their names and functions are detailed below.

Vitamin A

Vitamin A's function is the growth and repair of body tissue and keeping the body's skin and mucous membranes healthy including the linings of the airways and the digestive tract. It is also necessary for strong bones, good eye sight (in particular at night) and healthy blood. Vitamin A occurs in two forms, one of animal and one of plant origin. The Vitamin A of animal origin is called retinol. Retinol can be used directly by our bodies. Retinol is a fat soluble vitamin and is found in fat, oil and meat. There is a very large amount of retinol in animal liver and fish liver oils. It is added to margarine.

The other form of Vitamin A is of vegetable origin and is called beta-carotene. It is found in strongly coloured fruit and vegetables including apricots, mangoes, canteloupe and water melons, carrots, spinach, sweet potatoes and broccoli.

Deficiencies in Vitamin A lead to night blindness, skin problems, fatigue and diarrhoea. However, it is possible to overdose on Vitamin A. The majority of people will take in more Vitamin A than they need through a standard diet and supplements are not usually required.

Vitamin B

Vitamin B is the global name given to a number of related chemicals (see below). All the B vitamins are water soluble. They work together to help break down carbohydrates into glucose, metabolise fats and protein and ensure the correct functioning of the central nervous system. In addition, they are connected with the health of skin, hair, blood and the digestive tract.

The best known and studied B vitamins include:

• Vitamin B1 (Thiamin). Rich sources of thiamin include wholemeal bread, brown rice, yeast and oatmeal. Fruit and green vegetables also contain B1. A deficiency of B1 can lead to beriberi, a disease of the nervous system. The word "beriberi" originates from a Sri Lankan phrase that means "I can't, I can't".
• Vitamin B2 (Riboflavin). Rich sources of Riboflavin include cabbage, lettuce, liver, yeast, liver, milk, yoghurt, cheese and wholegrain cereals. It should be noted that B2 is destroyed by exposure to ultra-violet light, so milk should not be left on the doorstep too long! A deficiency in B2 leads to symptoms in the eyes, including light sensitivity, and itchy or gritty feeling or conjunctivitis.
• Vitamin B3 (Nicotinic Acid). The body can convert the protein trytophan into B3. Sources of trytophan include milk and eggs. The main direct sources of B3 in the diet include meat and cereals. A deficency in B3 can lead to a disease called pellagra, whose symptoms include dementia, diarrhoea, skin and sleep problems. It is virtually unheard of in the Western World, although still occurs in parts of China, Africa and India.
• Vitamin B6 (pyridoxine). Rich sources of vitamin B6 include tuna, bananas, poultry, spinach and fish. A deficiency can lead to fatigue, anaemia, skin problems and fits.
• Vitamin B12 (also known as cobalamin due to its cobalt content). It is made by bacteria in the body from foods of animal origin, ie meat and dairy products. Vegans, who eat no animal products at all, will need to take a vitamin B12 supplement. A deficiency in B12 will lead to anaemia and possible irreversible nerve damage.
• Folic Acid (folate) - this B vitamin is found in green vegetables, oranges, bananas and yeast extract. However, cooking destroys this vitamin, so many cereals are fortified with it. It is adviseable for women thinking of having a family to take a folic acid supplement before and during pregnancy (up to week 12). Taking folic acid dramatically reduces the risk of birth defects of the brain and spine, including spina bifida. The current recommendation is a supplement containing 0.4 mg of folic acid (ie 400 microgram).
• Biotin - this vitamin is found in leafy green vegetables, liver, kidney, milk, dried fruit and egg yolk.
• Pantothenic Acid - the richest sources of this vitamin include oily fish, eggs, kidney, yeast, liver and wholegrains. However, a deficiency of this vitamin has never been identified in man (although it has in animals).

Vitamin C (Ascorbic Acid)

Vitamin C is a water soluble vitamin. It is found in fruit and vegetables - the richest sources include blackcurrants, strawberries, citrus fruits, peppers, sweet potatoes and kiwi fruit. Vitamin C is essential for the formation of connective tissue in the body, which holds together skin, bone, tendons and ligaments. It also aids healing and prevents haemorrhaging. In addition, it aids the absorption of iron from none animal sources and is an antioxidant, meaning that it prevents some other vitamins oxidizing (decaying).

A deficiency of Vitamin C can cause bleeding gums and ultimately leads to scurvy, which causes liver spots and bleeding from the mucous membranes, eventually resulting in death.

Vitamin C cannot be stored in the body and needs to be eaten every day. Excess Vitamin C is excreted through urine. Vitamin C can be destroyed by overcooking and leached into water used to cook vegetables. Even storing vegetables for extended periods or cutting them reduces the Vitamin C content.

Many people believe that large doses of Vitamin C can prevent or cure the common cold, but there is no scientific evidence to support this.

Vitamin D

Vitamin D is known as the "sunshine vitamin", because it forms under our skin when ultra violet rays reach the skin's surface. It is a fat soluble vitamin, and is found in oily fish and butter. It is also added to margarine, powdered milk and breakfast cereals. Vitamin D promotes the absorption of calcium for the repair and growth of bone. The calcium is largely obtained from milk. A lack of vitamin D causes rickets, where the leg bones cannot support the body's weight giving rise to a bow-legged appearance. Bone softening and dental problems may also be a result of a lack of Vitamin D. In excessive quantities, Vitamin D is poisonous. However, the following groups of people may require a Vitamin D supplement of 10 micrograms (0.01 mg) per day:

• Women who are pregnant or breastfeeding
• People who avoid the sun or always cover up when outdoors
• People who don't eat oily fish or meat

If you are in doubt about whether a supplement is appropriate for you, talk to your doctor.

Vitamin E

Vitamin E is fat soluble and is widely available in most foods so a deficiency would be difficult. The richest sources of Vitamin E include vegetable oils, nuts and wheatgerm. Like Vitamin C it acts as an antioxidant. There are various types of Vitamin E and all are known as tocopherals. alpha-tocepheral promotes fertility in rats which is why some health food shops sell Vitamin E, usually in the form of wheatgerm oil, to promote fertility in humans. However, nutritionists and scientists are sceptical of such a link.

The main function of Vitamin E in the body is to aid the transport and effective use of oxygen in the bloodstream.

Vitamin K

Vitamin K is fat soluble and the richest sources of this vitamin include spinach, broccoli, cereal and vegetable oil, although it is also produced by bacteria in the gut. It is necessary to promote the correct clotting of blood and wound healing.

Vitamin K is given as an injection to new born babies to prevent a rare illness called Haemolytic disease. This illness would affect about one in ten thousand babies if they did not receive Vitamin K, but it can be fatal. Some parents choose to have the vitamin administered via oral drops instead of by injection.

See: Vitamins and Minerals.