 | Some trace minerals are difficult to
detect in humans, and it is often hard to determine the
exact amount of a trace mineral in food. Deficiencies were
first observed in small, geographically isolated groups
(e.g., selenium deficiency in an area of China) or people
nourished exclusively by total parenteral nutrition that
did not contain sufficient trace minerals. |
| Iron is a critical component of
hemoglobin, myoglobin, and cytochromes. Iron acts as a
cofactor for several enzyme systems. Two-thirds of the
body's iron is found in hemoglobin in red blood cells,
where its job is to transport oxygen from the lungs to the
tissues. A prolonged low intake of iron can lead to
decreased production of red blood cells and a lack of
oxygen being delivered to the tissues. This condition is
called iron deficiency anemia, which results in fatigue
and apathy, as well as decreased learning ability in
children. |
| The absorption of iron depends on the
body's need for the mineral and on the form of iron in
food. The body cannot readily excrete excess iron, but the
body has evolved a mucosal block, which limits
overabsorption. Heme iron from animal foods is better
absorbed than nonheme iron obtained primarily from plant
sources. the best sources of dietary iron are animal
protein, including beef and other dark meats, oysters,
liver, and broccoli. |
| Girls and women have a higher RDA for
iron than men because of menstrual blood loss. Infants and
children who live in poverty are often iron deficient
because of a lack of heme iron in the diet. |
| Iron toxicity occurs because of a genetic
disorder called hemochromatosis, which causes the
overabsorption of iron. A common form of poisoning also
occurs among toddlers and young children who swallow a
large number of iron pills. Death can occur. |
| Zinc functions as a cofactor for more
than nearly 100 enzyme systems, which are important for
growth, sexual development, immune function, wound
healing, and taste. A zinc deficiency results in growth
failure, loss of appetite, inadequate mental function, a
persistent rash, and decreased immune function. Zinc
deficiency is rare in the USA. |
| Like iron, the best dietary sources of
zinc are found in animal foods. Need drives absorption.
And like iron, there is a mucosal block in the intestinal
cells, which regulates the amount of zinc that can be
absorbed. Calcium, copper, and iron in supplement form can
interfere with zinc absorption. The richest source of zinc
is oysters. Other animal proteins are excellent sources.
Plant sources are whole grains, peanuts, and legumes. |
| Copper aids in iron absorption and
mobilization from body stores. Copper is responsible for
the cross-linking in collagen formation and for nerve cell
myelination, and it acts as part of an enzyme that is a
scavenger for free radicals. A copper deficiency can
result in a secondary iron deficiency. Copper is found in
liver, cocoa, legumes, and whole grains. The copper
content of the soil where a plant is grown affects the
copper content of the plant food. |
| Selenium acts as a cofactor for the
enzyme glutathionine peroxidase, which protects cells
against destruction by hydrogen peroxide and free
radicals. In some instances, selenium can replace some of
the need for vitamin E. Human deficiency is rare in the
USA. The selenium content of the soil where a plant is
grown greatly affects the selenium content of the plant
food. In a few areas of China where the soil is selenium
poor, the inhabitants experience selenium deficiency.
Meat, eggs, fish, and shellfish are sources of selenium.
Plant sources include grains and plant seeds. |
| Iodide forms part of the thyroid
hormones, one being thyroxine. Thyroid hormone controls
the basal metabolic rate. A lack of dietary iodide causes
an enlarged thyroid gland, known as goiter. the iodide
content of the soil where a plant is grown greatly affects
the iodide content of the plant food. Iodide deficiency at
one time was common in areas around the Great Lakes of
North America because the soil is iodide poor. Today,
iodide deficiency in the USA is virtually unknown because
of the fortification of table salt with iodide, but there
is some concern about iodide status in pregnant women. |
| Fluoride exposure makes tooth crystal
resistant to dental caries, and fluoride in saliva aids in
the remineralization of damaged tooth surfaces. Most North
Americans receive fluoride from fluoridated drinking water
and toothpaste. |
| Chromium contributes to the action of
insulin. Chromium is found in meats and whole grains. |
| Manganese function in several important
enzyme systems. Deficiency is rare. Whole grains, legumes,
and animal foods are reliable food sources. |
| Molybdenum is found in several enzyme
systems. Deficiency is rare. Molybdenum is found in plant
foods such as legumes and whole grains. |
| Boron contributes to ion transport in
cell membranes. Fruits, leafy vegetables, nuts, and beans
are sources. |
| Nickel likely participates in amino acid
metabolism. Nickel is found in nuts, beans and whole
grains. |
| Silicon is involved in bone formation.
Root vegetables and whole grains are sources. |
| Arsenic likely participates in amino acid
and DNA metabolism. Fish, grains, and cereal products are
sources. |
| Vanadium likely has insulin-like actions
in the body. Shellfish and mushrooms are sources. |
