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Essential trace elements range from metals to non-metals. What makes
them essential is their variable oxidation state. They are important
parts of oxidative-reduction enzymes in the body. They also have roles
in transport proteins, cofactors, and detoxification and defense. Trace
elements are carried bound to transport proteins in the blood. Because
they are generally toxic when in free form, they are transported bound
from entry to exit within the body.
Iron
Iron is important in the transportation of oxygen from the lungs
by way of the blood stream to the tissues. It is present in the red
blood cell protein, hemoglobin.
A similar protein in muscle, myoglobin,
also contains iron and stores oxygen for use during muscle contraction.
Iron is found in the portion of the cell involved in energy production
and as a cofactor for several enzymes.
Deficiency
Iron deficiency generally occurs during the growth period or when intake
fails to replace iron loss that is associated with blood loss. When iron
stores are depleted and there is inadequate production of heme (the
portion of hemoglobin associated with the iron), the red blood cells
become small (microcytic) and have decreased capacity to carry oxygen.
There is also a drop in iron-containing enzymes that are important in
cellular metabolism. This results in decreased work capacity, fatigue
and altered behavior such as irritability.
Toxicity
Iron poisoning is the most common cause of death resulting from
poisoning in children. Supplemental iron can cause gastric irritation,
abdominal pain, constipation,
diarrhea, nausea and vomiting. Certain antacids
may decrease the absorption of iron supplements.
The RDA for iron in males over 19 years is 10 mg; for females of 11-50
years, 15 mg; for females over 51 years, 10 mg; for pregnant females, 30
mg; and for lactating females, 15 mg. Not all forms of iron are the
same: 1 gram of ferrous gluconate = 120 mg elemental iron; 1 gram
ferrous sulfate = 200 mg elemental iron; and 1 gram of ferrous fumarate
= 330 mg elemental iron.
Zinc
Zinc is important in growth, appetite, development of the testicles, skin integrity, mental
activity, wound healing, and
proper functioning of the immune system. Zinc is a cofactor for many
enzymes, which means that zinc is necessary for the proper functioning
of these enzymes. These enzymes participate in the metabolism of
carbohydrates, lipids, proteins and nucleic acids (such as DNA). Zinc is
involved in the functioning of the immune system and in the expression
of genetic information. Zinc is present in bone and is involved in the
regulation of bone
calcification. It is also present in members of a class of proteins
called the metallothioneins that are believed to provide antioxidant
protection by scavenging free radicals.
Recently zinc lozenges have been used to reduce the duration or severity
of the common cold and other upper respiratory tract infections of viral
origin. Investigations are underway to verify these claims. Zinc
lozenges can cause mouth irritation, nausea and diarrhea. The lozenges
should not be used more than one week. The unpleasant taste of the
lozenges is a frequent complaint. When applied topically, zinc acts as
an astringent and a weak antiseptic. Zinc oxide is used topically as a sunblock
and to treat skin conditions such as chafing, diaper rash, and minor
skin irritations.
The RDA of zinc for males 11 years and older is 15 mg; for females 11
years and older, 12 mg; for pregnant females, 15 mg; for lactating
females during the first 6 months, 19 mg; and during the second 6
months, 16 mg.
Deficiency
A zinc deficiency may be associated with diets high in unrefined cereal
and unleavened bread, long term IV nutrition, or diseases of the
intestine such Crohn's
disease, alcoholism, or pregnancy.
Toxicity
Toxicity from zinc supplements can cause flu-like symptoms, fever,
epigastric pain, fatigue, vomiting, dehydration, anemia, depressed
immune function and decrease in the "good" form of
cholesterol. Excessive zinc interferes with the function of copper and
iron.
Iodine
Iodine is absorbed well, circulates both free and bound, and is
sequestered in the thyroid gland where it is incorporated into the thyroid
hormones, triiodothyronine (T3) and thyroxine (T4). These hormones
are important in regulating the basal metabolic rate (associated with
energy production) of adults, and the growth and development of
children. Iodine is sometimes used to help thin secretions from the lung
in order to help expel the secretions. It is used on the skin
as an antiseptic, although it may stain the skin, irritate tissues and
cause sensitization in some people.
Deficiency
Deficiency is manifest by a decreased metabolic rate, lethargy and obesity.
A prolonged deficiency of iodine causes the thyroid gland to increase in
size such that a large nodule referred to as a goiter, protrudes from
the neck. In many countries inorganic iodides are added to table salt to
prevent the deficiency. Iodine deficiency in infants and children
results in mental retardation. Inadequate maternal intake causes a
deficiency in the fetus and newborn. Early recognition of the syndrome
is key to minimizing mental retardation. Some plants produce goitrogens
(cabbage, plantain). These substances fool the thyroid and inhibit the
synthesis of the thyroid hormones. Arsnic can also inhibit the synthesis
of thyroid hormones by interfereing with normal thyroid function.
Toxicity
High doses of iodides (the salts of iodine) inhibit thyroid hormone
synthesis and release. As lack of iodine leads to symptoms of thyroid
deficiency, so do excessive doses of iodides. It is sometimes used to
treat hyperthyroidism. With prolonged excessive intake, a goiter can
occur. Sometimes a large dose of iodides is given before thyroid surgery
to shrink the size of the thyroid gland.
Some people are hypersensitive to iodine and this can lead to skin
rashes, mucous membrane ulcers, a fever, "iodism" (metallic
taste, gastric irritation, burning mouth and throat, sore teeth and
gums, symptoms of a head cold), and swelling in the neck area. Iodine
supplements can cause acne.
Health food formulations containing kelp can also cause acne due to the
high content of iodine.
The RDA for iodide in males and females over 12 years is 150 mg; for
pregnant females, 175 mg; and for lactating females, 200 mg. The content
of iodide in iodized table salt is 76 mg/g of salt; therefore with an
average use of 3.4 g per day, approximately 200 mg of iodide is
consumed.
Chromium
Chromium is an essential trace element that is needed for carbohydrate,
fat, and nucleic acid (DNA or RNA) metabolism. Main sources in the diet
include whole grains, egg yolks, brewer's yeast, liver, meats, and nuts.
Signs of a chromium deficiency are usually only seen in adults eating
highly refined foods or in people who are receiving long-term IV
nutrition that lack chromium. With a chromium deficiency, blood sugar
levels are generally high. There may also be abnormalities of nerve
stimulation of the extremities (arms, hands, legs and feet) and
alterations of brain tissue.
There are some people with type 2 (non-insulin dependent) diabetes
that appear to have improved blood sugar control with chromium
supplementation, but this is not seen in all diabetics. Chromium is part
of the glucose tolerance factor (GTF) that is required for insulin
action, however more thorough studies need to be conducted before
supplementation in diabetics becomes a general recommendation. There is
no scientific basis for the use of chromium supplements by athletes to
increase muscle mass or to reduce body fat. Chromium supplements may
lower cholesterol and triglycerides in people with diabetes as well as
with nondiabetics, but it may take months before this result is seen and
the effect may not be substantial. Chromium appears to affect some of
the enzymes that regulate cholesterol synthesis. The mechanism by which
chromium participates in proper nerve function is not well understood.
Chromium picolinate is the most well absorbed form of chromium currently
available. The RDA is 50 to 200 micrograms. Not many side effects have
been reported from the use of chromium supplements unless excessive
doses are taken. This has resulted in liver and kidney
failure, anemia, muscle breakdown and abnormalities in blood
clotting. People with impaired kidney function should seek medical
advice before taking supplements.
Cobalt
Cobalt has a central action in vitamin B12 function. Meats
provide cobalt as a component of vitamin B12. If the vitamin
B12 requirement is met, then the cobalt requirement is met.
It is not known if cobalt has other functions. An RDA has not been
established. Cobalt can be toxic to humans because it is not regulated
at the point of absorption. Excess cobalt can cause polycythemia
(increased red blood cells), bone marrow hyperplasia, pancreatic failure
or congestive heart failure.
At large doses it also interferes with the absorption of iron.
Copper
Copper is incorporated into many enzymes and is necessary for their
actions. For example, the copper containing ceruloplasmin is involved in
the transport of iron in the blood to places where hemoglobin synthesis
occurs. Another enzyme is involved in maintaining connective tissue
integrity, and in copper deficiency, defective bone matrix and osteoporosis
may occur.
Deficiency
Although a deficiency is rare, it can occur in people with prolonged diarrhea
or other disorders of intestinal absorption. It can also occur in the
presence of high dose zinc supplementation. Signs of a deficiency
include anemia, a decrease in certain white blood cells, skeletal
demineralization, loss of hair color,
and skin pallor. Children
with copper deficiencies may experience ruptured blood vessels, central
nervous system abnormalities, growth retardation, and poor temperature
regulation.
Toxicity
Excessive doses of copper can cause diarrhea, epigastric pain and
discomfort, blood in the urine, liver damage, low blood pressure and
vomiting. No RDA has been established for copper.
Two diseases are associated with abnormal copper metabolism: Wilson’s
disease is marked by high levels of copper, especially in the brain,
liver, kidney and eye; Menke’s kinky hair syndrome results from
defective transport of copper into the blood of male infants and is
associated with retarded growth and a kinky appearance of the hair.
Manganese
Manganese assists in the activity of many enzymes, including some
involved in lipid, protein, and carbohydrate metabolism.
Deficiency
Manganese deficiency has not been well documented in humans. A few
people on manganese deficient diets showed signs of elevated calcium and
phosphorus, suggesting that dissolution of bone to release manganese
stores may also release calcium and phosphorus into the blood. As such,
it is speculated that a manganese deficiency may be a contributing
factor for osteoporosis.
In animals, a deficiency has been associated with abnormal reproductive
ability, growth retardation, birth defects, abnormal formation of bone
and cartilage, dermatitis, and
impaired glucose handling.
Toxicity
Chronic poisoning from manganese inhalation by miners has caused
dementia, psychiatric disorders similar to schizophrenia, and
neurological changes resembling Parkinson’s disease. Iron and
manganese affect the absorption of each other. Chronic liver disease can
cause manganese accumulation and toxicity. No RDA has been established
for manganese.
Molybdenum
Molybdenum is part of the molecular structure of several enzymes. One of
these enzymes is involved in the formation of sulfate. Under normal
circumstances, there have been no reports of molybdenum deficiency. In
patients maintained solely on IV nutrition that lack molybdenum for
prolonged periods, headache, irritability, lethargy and coma have
occurred but have been rapidly reversed upon addition of molybdenum. An
excess of molybdenum interferes with copper and iron
absorption. No RDA has been established for this element.
Selenium
Selenium is an essential nonmetallic element. Foods containing selenium
include meat, poultry, grains, and seafood. Some reports have suggested
that selenium may protect against certain types of cancer,
but large trials in humans are needed to support this. Selenium is
important for the function of several proteins. One of these is glutathione
peroxidase, an enzyme that prevents oxidative damage to cells from a
variety of peroxides. Selenium also appears to bind to some minerals
such as arsenic and mercury and decrease their toxicity.
Deficiency
Although selenium deficiency is uncommon in the United States, low
levels in the body may be associated with acute illness and prolonged IV
nutrition. Symptoms of selenium deficiency include muscle
weakness and pain, inflammation
of the muscles, fragile red blood cells, degeneration of the pancreas,
and abnormal coloration. There have also been associations of selenium
deficiency with several diseases affecting the heart muscle, but a
protective effect against heart disease has not been proven. In
geographic areas where selenium is deficient in the soil and therefore
in food, human deficiencies have been reported to cause dilation of the
heart and congestive heart
failure.
Toxicity
Side effects with high doses of selenium supplements include hair
and nail loss, skin
lesions, fatigue, irritability, liver and kidney damage, nausea,
vomiting and abnormal blood clotting. Animals in the west grazing on
plants that have accumulated selenium show acute or chronis selenium
poisoning. Chronic selenium toxicity (alkaline disease) is characterised
by muscle degeneration, rough coat, labored breathing and cardiovascular
failure. Acute selenium toxicity (blind staggers) manifests as weight
loss, anorexia, excessive salivation, jaundice or necrosis of the heart
and liver.
For cancer prevention, a typical dose of selenium is 200 micrograms per
day. The RDA for women over 19 years is 55 micrograms; for pregnant
women, 65 micrograms; for lactating women, 75 micrograms; and for men
over 19 years, 70 micrograms.
Fluoride
Fluoride may not actually function as an essential trace element but it
has beneficial effects on skeletal and dental
health. Fluoride assists in the prevention of tooth decay. It works
by increasing the tooth resistance to acid, promoting remineralization,
and inhibiting the process by which bacteria promote cavities. There is
also evidence that fluoride helps protect against osteoporosis.
It is associated with a decrease in bone demineralization. Fluoridation
of the water supply is an effective method for providing fluoride. Oral
supplements are available for people that do not have access to
fluoridated water. Although there is no RDA for fluoride, the protective
effect of fluoride for teeth occurs at an intake of 1.5 mg/day or more
for adults. Intakes over 2.5 mg/day in children may cause mottling of
the teeth.
Toxicity
Acute toxicity has occurred by ingestion of household products
containing high levels of fluoride such as certain insecticides. The
mechanism of fluoride toxicity is conversion in the stomach to
hydrofluoric acid. Gastrointestinal symptoms predominate and include nausea,
vomiting, diarrhea, and abdominal pain. Chronic ingestion of high
amounts of fluoride during tooth development results in dental fluorosis
and mottling of teeth. It can also result in increased density and
calcification of bone, and in severe cases is referred to as crippling
skeletal fluorosis.
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