What it does: Contrary to popular belief, Vitamin C doesn't prevent colds and flu, but it can reduce the length and severity of symptoms. Vitamin C acts as an antioxidant. This means it protects the body against disease including heart disease and cancer. It is vital for the production of collagen, used to build body tissue and bones.
Main food source: If you eat a wide range of fresh fruit and vegetables every day you will have a balanced intake of vitamin C. Citrus fruits, kiwi fruit, strawberries and cranberries are an excellent source of vitamin C. Green vegetables (cabbage, broccoli and beans) and potatoes all contain high levels.
How to take supplements: The recommended dose of Vitamin C is 40 milligrammes (mg) a day for adults and 25 mg a day for children. Powder form tends to be acidic, but cheaper than tablet form. Stir vitamin C powder into yoghurt for children.

Iron

What it does: Iron is essential for the formation of red blood cells which carries oxygen around the body. A good intake of iron is necessary for energy, intellectual performance and vitality. A lack of iron leads to anaemia - where the body is unable to transport oxygen around the body causing lethargy and listlessness. Excessive iron may damage organs.
Main food source: Red meat is a rich source of iron. Other sources include cereal products, bread, flour, eggs, beans, lentils and dried fruit. Taking Vitamin C alongside iron helps with its absorption.
How to take supplements: People who don't eat red meat, suffer heavy menstrual cycles or blood loss after surgery should take iron pills to boost formation of blood cells and combat lethargy. Iron also comes in liquid form (available at good health stores) specially mixed for pregnant women, children and older people. The recommended daily dose is 15 mg for women, 9 mg for men and 2-9 mg for children.

Vitamin A

What it does: Vitamin A is important for repairing tissues needed for growth and development. It is also essential for strengthening the immune system and maintaining good eyesight.
Main food source: Milk, fortified margarines, egg yolks, liver, fatty fish (herrings, tuna, pilchards and sardines), carrots, tomatoes, green leafy vegetables, mango and apricots all provide vitamin A.
How to take supplements: Too high doses of vitamin A can prove toxic and cause problems with the liver and complications during pregnancy. The recommended daily intake is 600 microgrammes for women and 700 microgrammes for men.

Vitamin E

What it does: Vitamin E acts as an antioxidant protecting cell membranes from damage, and is thought to protect against some cancers and heart disease.
Main food source: Nuts and oil are an excellent source of vitamin E. Green leafy vegetables (broccoli, spinach and cabbage) and cereals are also rich in vitamin E.
How to take supplements: Deficiency is rare since vegetable oils are rich sources of vitamin E. The recommended daily intake for adults is 10 mg.

Selenium

What it does: An essential mineral that makes up part of the enzymes that defend the body against damage. As an antioxidant it strengthens the immune system and is thought to protect against cancer, especially of the prostate.
Main food source: Cereals, meat, fish and Brazil nuts.
How to take supplements: Selenium is included in many multivitamin supplements. The recommended daily intake is 200 microgrammes.