Around a quarter of the naturally occurring elements are essential to body functioning. Some are needed in large quantities, like sodium (Na), potassium (K), calcium (Ca), and phosphorus (P) to take part in physiological reactions such as nerve impulse transmission or to form body structures such as bones and teeth. However, other elements are needed only in smaller, trace amounts.

Trace elements are needed by the body in only minute quantities but are absolutely vital to maintain good health. For example:

• F (Fluorine) is necessary for adequate tooth formation.

• I (Iodine) is necessary for the formation of a hormone that controls metabolism known as thyroxine, produced by the thyroid gland in the neck.

Iron (Fe) is an important component of haemoglobin, the blood pigment, but because of the efficient recycling of existing iron within the body only a very small quantity - about 1 to 2 mg per day - is needed in addition.

Deficiencies of trace elements can result in serious health problems. For example, a lack of iodine in the diet can cause a goitre or swelling in the neck (see the illustration alongside), as the thyroid gland tries to compensate for the lack of the trace element but is unable to finish making thyroxine. This highlights the importance of even small amounts of certain substances to the body.

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