The Foundations of Chemistry

23-3 Uses of Group IA Metals and Their Compounds 925

CC The Development of Science

HEMISTRY IN USE

Trace Elements and Life

More than 300 years ago iron was the first trace element

shown to be essential in the human diet. An English physi-

cian, Thomas Sedenham, soaked “iron and steel filings” in

cold Rhenish wine. He used the resulting solution to treat

patients suffering from chlorosis, now known to be an iron-

deficiency anemia. Nearly 20 trace elements are now believed

to be required by humans. The discovery of the biological

functions of trace elements is an exciting and controversial

area of human nutrition research.

The trace elements can be classified into several categories

(see table). In 1989, the National Research Council recog-

nized that iron, iodine, zinc, selenium, copper, chromium,

manganese, and molybdenum were dietary essentials for

humans. Fluorine is also considered to be valuable for human

health, because of its benefits to the teeth and skeleton. These

nine trace elements are required by humans and other

animals because they are essential components in metalloen-

zymes and hormones or because they promote health in a

specific tissue (such as fluorine in the teeth and skeleton).

The trace elements required by the human body in milligram

quantities include iron, zinc, copper, manganese, and fluo-

rine. Trace elements required in microgram (g) quantities

include iodine, selenium, chromium, and molybdenum.

Although probably required in g quantities, no dietary rec-

ommendations have been made for arsenic, nickel, silicon,

and boron even though there is evidence, primarily from ani-

mals, that they are essential. There is only weak evidence that

cadmium, lead, lithium, tin, vanadium, and bromine are

essential for humans.

Iron deficiency is one of the most common nutrient defi-

ciencies in the world, occurring in up to 60% of the women,

infants, and children of some countries. Anemia, character-

ized by a low concentration of hemoglobin in the blood or

by a low volume of packed red blood cells, is the usual symp-

tom of iron deficiency. Other symptoms include fatigue and

cognitive disorders. Up to 1% of the population may have

the genetic disease known as hereditary hemochromatosis,

which results in excess absorption of dietary iron, and can

lead to liver and heart damage. Concern about this disease

may eventually lead to routine screening so that persons with

this disorder can be treated before severe symptoms develop

and can avoid foods and supplements with large amounts of

iron. The recommended dietary allowance for iron for

women aged 23 to 50 years is 50% higher than that for men

in the same age group because of the iron lost in menstrual

bleeding.

Many dietary supplements include essential trace

elements.

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