Biology of Disease

an important renal buffer. Sulfate is required for the synthesis of cartilage and
other components of the extracellular matrix.

Compared with minerals, trace elements are required in much smaller
quantities, but like them are supplied by a variety of foods (Table 10.5). Trace
elements include iron, cobalt, copper, molybdenum, chromium, manganese,
zinc, selenium, iodide and fluoride. They are present in the body at
concentrations less than 100 parts per million and are required in milligrams
or even micrograms per day and a number are toxic in excess.

Trace elements have specific and diverse functions. Chromium helps maintain
blood glucose concentration by acting as a cofactor for insulin activity. The
role of cobalt as a component of vitamin B 12 , has already been mentioned.
Copper is also an essential cofactor for a number of enzymes, including those
involved in collagen and elastin synthesis and some redox proteins. Copper is
also required for iron absorption and metabolism and hemoglobin synthesis.
Fluoride is necessary for the ‘hardening’ of bone and teeth. All the thyroid
hormones contain iodine as described in Chapter 7. Iron is a component of
the prosthetic group, heme found in hemoglobin and myoglobin, where it
maintains its oxidation state and binds a dioxygen molecule. Iron is also found
in the heme of cytochromes and in nonheme iron proteins involved in electron
transfer, where, of course, its oxidation state does alter. Manganese is essential
for the activities of a number of enzymes. For example, pyruvate carboxylase and
phosphoenolpyruvate carboxykinase function in gluconeogenesis; arginase is a
key enzyme of the urea cycle that detoxifies ammonia produced during amino
acid metabolism and superoxide dismutase is a major antioxidant defence.
Enzymes that contain molybdenum are common and catalyze several reactions
in purine metabolism, for example xanthine oxidase, and maintains the
synthesis of sex hormones. Selenium is a cofactor in, for example, glutathione
peroxidases, and zinc in carbonic anhydrase and RNA polymerase.

DIET AND NUTRITION

CZhhVg6]bZY!BVjgZZc9Vlhdc!8]g^hHb^i]:YLddY '*&

Trace element Recommended intake

/mg day–1

Sources

Chromium 0.025 in adults meats, cheese, water, whole grains, lentils,

spices

Cobalt 0.0015 in adults beef, eggs, offal, fish, milk products, nuts,

vegetables, cereals

Copper 1.2 in adults offal, fish, nuts

Fluoride diet generally adequate present in drinking water in many areas of the

world

Iodide 0.14 in adults fish, milk, eggs , cereals, iodized salt

Iron 8.7 in males

14.8 in females

liver, meat, eggs, beans, nuts, dried fruit,

brown rice, green vegetables and fortified

cereals

Manganese diet generally adequate bananas, egg yolk, bread, nuts, cereals,

vegetables, tea

Molybdenum diet generally adequate whole grains, leguminous vegetables, meats

Selenium 0.075 in males

0.06 in females

fish, meat, offal, Brazil nuts and eggs

Zinc 5.5 to 9.5 in males

4.0 to 7.0 in females

meat, offal, eggs, fish, cereals, milk, cheese,

spinach, beans

Table 10.5Recommended intakes and sources of trace elements