Vitamins

Key points

• Vitamins are nutrients that are needed in tiny amounts.
• Vitamins have many roles in the body.
• The body can make vitamin D in the skin when it is exposed to sunlight.
• The amount of each vitamin we need changes during a lifetime.

What are vitamins?
Vitamins are complex organic substances that are needed in very small amounts for many of the essential processes carried out in the body. Usually only a few milligrams (mg) or micrograms (μg) are needed per day, but these amounts are essential for health. Most vitamins cannot be made by the body, so have to be provided by the diet. An exception is vitamin D which can be obtained by the action of sunlight on the skin.

Vitamins have a variety of functions in the body: some are co-factors in enzyme activity, some are antioxidants (prevent oxygen from doing damage in the body) and one (vitamin D) is a pro-hormone.

Vitamins have been traditionally grouped into two categories: the fat soluble vitamin, and the water soluble vitamins. Originally, vitamins were given letters (A, B, C, etc.) but now are usually referred to by their chemical names, e.g. folate.

How much of the vitamins do we need?
The body requires different amounts of each vitamin because each of them has a different function. People have different requirements too, according to their age, gender level of activity and state of health.

Vitamin supplements
Although most people are able to meet their requirements for vitamins by eating a varied diet, there are certain groups of the population who have higher than normal requirements, e.g. the sick, those taking certain drugs and pregnant women, such people need to ensure they eat foods rich in particular vitamins and sometimes supplements are advised. Infants and young children are recommended to have supplements of vitamins A and D for at least 2 years. Some women many require additional iron if menstrual losses are high.

Further information
Henderson L et al (2003) The National Diet and Nutrition Survey: Adults Aged 19-64 years, Volume 3: Vitamin and Mineral Intake and Urinary Analysis. London, HMSO.

Stanner, S et al (2004) A review of the epidemiological evidence for the 'antioxidant hypothesis'. Public Health Nutrition 7(3):407-22

© British Nutrition Foundation