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THEENERGY
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overview of The MicronuTrienTs
Overview of the Micronutrients 281
overview of The MicronuTrienTs
Can food be medicine? Consider the following examples:
• Fatigue, bleeding gums, bruising, and scaly skin . . . these are the symptoms of
scurvy, which plagued seamen during long ocean voyages until 1753, when
James Lind, a physician in the British Navy, identified that consumption of citrus
fruits could prevent this disease.
• Imagine the epidemic of rickets that occurred among children in post-Industrial
Revolution Britain during the late eighteenth century. They suffered from bone
pain; frequent fractures; weakness; and deformities, such as bowed legs. In 1922,
cod liver oil was determined to be an effective treatment for rickets.
• First noted in medical literature in the mid-sixteenth century, chlorosis was a disorder characterized by a green skin color, extreme weakness, and poor appetite.
Chlorosis was mainly described among adolescent women, so some physicians
of the era declared it to be a hysterical condition. In the early 1700s, the British physician Thomas Sydenham prescribed that afflicted women should drink
“mineral water impregnated with the Iron Mine.”
How do citrus fruits, cod liver oil, and mineral water prevent or cure such serious
ailments? As nutrition science has evolved, the discovery of essential compounds
in the foods we eat has overturned old misconceptions about the origins of some
diseases. These essential compounds are collectively known as micronutrients. Citrus fruits, sure cures for scurvy, contain vitamin C. Cod liver oil, a preventive treatment for rickets, is an excellent source of vitamin D. The mineral water prescribed
by Sydenham supplied iron for his patients suffering from chlorosis, a form of irondeficiency anemia.
Vitamin C, vitamin D, and iron are a few examples of micronutrients. In Chapters 4, 5, and 6, you learned about carbohydrates, lipids, and proteins. Along
with water, these energy-yielding nutrients are known as macronutrients. These
are essential components needed in relatively large amounts (grams) in the
human diet. On the other hand, micronutrients yield no energy and are required
in small amounts (milligrams or micrograms). However slight its requirement,
each micronutrient is necessary for one or more functions in the body (Overview
Fig. 1). Too little or too much of any specific micronutrient leads to deterioration
of physical health.
The micronutrients can be chemically grouped based upon the presence of carbon
atoms bonded to hydrogen atoms in their chemical structures. Organic micronutrients
are classified as vitamins and inorganic micronutrients are classified as minerals.
By definition, vitamins are essential organic (carbon-containing) substances
needed in small amounts in the diet for normal function, growth, and maintenance of the body. In general, humans require a total of about 1 ounce (28 grams)
of vitamins for every 150 pounds (70 kilograms) of food consumed. Vitamins can
be divided into two broad classes based on solubility. Vitamins A, D, E, and K are
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characterized by weakness, fatigue, slow
wound healing, opening of previously
healed wounds, bone pain, fractures, sore
and bleeding gums, diarrhea, and pinpoint
hemorrhages on the skin.
rickets A disease characterized by poor
mineralization of newly synthesized bones
because of low calcium content. Arising in
infants and children, this deficiency is caused
by insufficient amounts of the vitamin D
hormone in the body.
chlorosis In traditional medical terminology, a form of iron-deficiency anemia characterized by pale or greenish skin, weakness,
fatigue, and shortness of breath. In modern
medical literature, chlorosis is termed hypochromic anemia.
micronutrient A nutrient needed in milligram or microgram quantities in a diet.
vitamin Compound needed in small
viTaMins: viTal DieTarY coMPonenTs
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scurvy The vitamin C deficiency disease
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amounts in the diet to help regulate and
support chemical reactions and processes in
the body.
mineral Element used in the body to promote chemical reactions and to form body
structures.
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overview figure 1 c Micronutrients
contribute to many functions in the body.
Bone Health
Energy
Metabolism
Vitamin C
Vitamin D
Vitamin K
Calcium
Phosphorus
Magnesium
Fluoride
Boron
Silicon
Thiamin
Riboflavin
Niacin
Pantothenic acid
Biotin
Vitamin B-12
Iodide
Chromium
Manganese
Molybdenum
Fluid and
Electrolyte
Balance
Antioxidant
Systems
Vitamin A
Vitamin C
Vitamin E
Carotenoids
Selenium
Zinc
Copper
Manganese
Sodium
Potassium
Chloride
Phosphorus
Blood
Health
Vitamin B-6
Vitamin B-12
Folate
Vitamin K
Iron
Zinc
Copper
fat-soluble vitamin Vitamins that dissolve in fat and such substances as ether and
benzene but not readily in water. These vitamins are A, D, E, and K.
water-soluble vitamins Vitamins that
dissolve in water. These vitamins are the B
vitamins and vitamin C.
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fat soluble (Overview Table 1), whereas the B vitamins and vitamin C are water
soluble (Overview Table 2). The B vitamins include thiamin, riboflavin, niacin,
pantothenic acid, biotin, vitamin B-6, folate, and vitamin B-12. Choline is a related
nutrient, but is not classified as a vitamin.
Vitamins are generally essential in human diets because they can’t be synthesized
in the human body or because their synthesis can be decreased by environmental
factors. Notable exceptions to having a strict dietary need for a vitamin are vitamin
A, which we can synthesize from certain pigments in plants; vitamin D, synthesized
in the body if the skin is exposed to adequate sunlight; niacin, synthesized from the
amino acid tryptophan; and vitamin K and biotin, synthesized to some extent by bacteria in the intestinal tract.
To be classified as a vitamin, a compound must meet the following criteria: (1)
the body is unable to synthesize enough of the compound to maintain health; and
(2) absence of the compound from the diet for a defined period produces deficiency
symptoms that, if caught in time, are quickly cured when the substance is resupplied.
A substance does not qualify as a vitamin merely because the body can’t make it. Evidence must suggest that health declines when the substance is not consumed.
As scientists began to identify various vitamins, related deficiency diseases such as
scurvy and rickets were dramatically cured. For the most part, as the vitamins were
discovered, they were named alphabetically: A, B, C, D, E, and so on. Later, many substances originally classified as vitamins were found not to be essential for humans and
were dropped from the list. Other vitamins, thought at first to be only one chemical
turned out to be several chemicals, so the alphabetical names had to be broken down
by numbers (B-6, B-12, and so on).
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Overview of the Micronutrients 283 overview Table 1 Summary of the Fat-Soluble Vitamins
Vitamin
Major Functions
RDA or Adequate
Intake
Dietary Sources
Deficiency
Symptoms
Toxicity
Symptoms
Vitamin A • Promote vision: Females: 700
Preformed Vitamin A:
• Night blindness
• Fetal (preformed night and color
micrograms RAE
• Liver
• Xerophthalmia malformations vitamin A and
• Promote growth
• Fortified milk
• Poor growth
• Hair loss provitamin A)
• Prevent drying Males: 900
• Fortified • Dry skin
• Skin changes of skin and eyes
micrograms RAE breakfast
• Bone pain • Promote cereals
• Fractures resistance to 2300–3000 IU if bacterial infection as preformed
Provitamin A:
Upper Level is and overall immune (vitamin A)
• Sweet potatoes
3000 micrograms system function
• Spinach
of preformed • Greens
vitamin A • Carrots
(10,000 IU) based • Cantaloupe
on the risk birth • Apricots
defects and liver • Broccoli
toxicity
Vitamin D
• Increase 5–15 micrograms
• Vitamin D
• Rickets in
• Growth absorption of fortified milk children retardation calcium and (200–600 IU)
• Fortified
• Osteomalacia
• Kidney damage phosphorus breakfast in adults
• Calcium • Maintain optimal cereals deposits in blood calcium • Fish oils soft tissue and calcification • Sardines of bone
• Salmon
Upper Level is 50 micrograms (2000 IU) based on the risk of elevated blood calcium
Vitamin E
• Antioxidant 15 milligrams
• Plant oils
• Hemolysis of
• Muscle prevents alpha-tocopherol
• Products made red blood cells weakness breakdown of from plant oils
• Nerve
• Headaches vitamin A and 22 IU natural
• Some greens degeneration
• Nausea unsaturated form, 33 IU
• Some fruits
• Inhibition of fatty acids
(synthetic form)
• Nuts and seeds vitamin K • Fortified metabolism breakfast cereals
Upper Level is 1000 milligrams (1100 IU synthetic
form, 1500 IU
natural form)
based on the risk
of hemorrhage
Vitamin K
• Activation of Females: 90 • Green
blood-clotting micrograms vegetables
factors
• Liver • Activation of Males: 120
• Some plant oils proteins micrograms
• Some calcium involved in supplements bone metabolism
• Hemorrhage
• Fractures
No Upper Level has been set Abbreviations: RAE = retinol activity equivalents; IU = international units
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OVERVIEW Table 2 Summary of the Water-Soluble Vitamins and Choline
Vitamin
Major Functions
RDA or Adequate
Intake
Dietary Sources*
Thiamin
• Coenzyme of 1.1–1.2
• Sunflower seeds
carbohydrate milligrams
• Pork
metabolism
• Whole and
• Nerve function enriched grains
• Dried beans
• Peas
Deficiency
Symptoms
Toxicity
Symptoms
Beriberi
• Nervous tingling • Poor coordination • Edema • Heart changes • Weakness
None Riboflavin†
• Coenzyme of 1.1–1.3
carbohydrate milligrams
metabolism
• Milk
• Inflammation of the
• Mushrooms mouth and tongue • Spinach
• Cracks at the corners • Liver of the mouth • Enriched grains
• Eye disorders
None Niacin
• Coenzyme of 14–16
energy milligrams
metabolism
(niacin
• Coenzyme of equivalents)
fat synthesis
• Coenzyme of fat breakdown
• Mushrooms
• Bran
• Tuna
• Salmon
• Chicken
• Beef • Liver • Peanuts • Enriched grains
Upper Level is
35 milligrams from supplements, based on flushing of skin Pantothenic acid
• Coenzyme of 5 milligrams
energy metabolism
• Coenzyme of fat synthesis • Coenzyme of fat breakdown
• Mushrooms
• No natural
• Liver deficiency • Broccoli disease or • Eggs symptoms Biotin
• Coenzyme of 30 micrograms
glucose production
• Coenzyme of fat synthesis
• Cheese
• Egg yolks
• Cauliflower
• Peanut butter
• Liver
Pellagra
• Diarrhea
• Dermatitis
• Dementia
• Death
None Most foods have some
• Coenzyme of 1.3–1.7
• Animal protein
Vitamin B-6†
protein milligrams foods
metabolism
• Spinach
• Neurotransmitter
• Broccoli
synthesis
• Bananas
• Hemogloblin • Salmon
synthesis
• Sunflower seeds
Many other functions
• Dermatitis
• Tongue soreness • Anemia • Depression Unknown • Headache
• Anemia
• Convulsions
• Nausea
• Vomiting • Flaky skin • Sore tongue Upper Level is 100 milligrams, based on nerve destruction • Green leafy • Megaloblastic
None likely Folate (folic acid)† • Coenzyme involved 400 micrograms
in DNA synthesis
(dietary folate vegetables anemia
equivalents)
• Orange juice
• Inflammation
Upper Level for Many other functions
• Organ meats of tongue
adults set at • Sprouts
• Diarrhea 1000 micrograms • Sunflower seeds
• Poor growth
for synthetic folic • Depressionacid (exclusive of food folate), based on masking of B-12 deficiency
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Overview of the Micronutrients 285 Vitamin
Major Functions
RDA or Adequate
Intake
Dietary Sources*
Deficiency
Symptoms
Toxicity
Symptoms
Vitamin B-12†
• Coenzyme of 2.4 micrograms
• Animal foods • Macrocytic
folate metabolism (not natural in plants) anemia
• Nerve function
Older adults and
• Organ meats
• Poor nerve vegans should use
• Oysters function Many other functions
fortified foods or • Clams supplements.
• Fortified, ready-to-eat breakfast cereals
None Vitamin C
• Connective tissue 75–90
• Citrus fruits
• Scurvy
synthesis
milligrams
• Strawberries
• Poor wound
• Hormone synthesis
• Broccoli healing
• Neurotransmitter Smokers should
• Greens
• Pinpoint synthesis
add 35 hemorrhages
• Possible antioxidant milligrams
• Bleeding gums
activity
Upper Level is 2 grams, based on development of diarrhea Choline†
• Neurotransmitter 425–550
synthesis
milligrams
• Phospholipid synthesis
Can also alter some diagnostic
tests
Widely distributed
No natural
Upper Level is 3.5 in foods and deficiency
grams per day synthesized by
based on devel- the bodyopment of fishy
body odor and
reduced blood
pressure
*Fortified ready-to-eat breakfast cereals are good sources for most of these vitamins and a common source of B vitamins for many of us.
These nutrients also participate in homocysteine metabolism, which in turn may reduce the risk of developing cardiovascular disease.
†
In addition to their use in correcting deficiency diseases, a few vitamins have also
proved useful in treating several nondeficiency diseases. These medical applications
require administration of megadoses, well above typical human needs for the vitamins. For example, megadoses of a form of niacin can be used as part of blood cholesterol-lowering treatment for certain individuals. Still, any claimed benefits from use
of vitamin supplements, especially intakes in excess of the Upper Level (if set), should
be viewed critically because unproved claims are common.
Plant and animal foods supply vitamins in the human diet. Vitamins isolated from
foods or synthesized in the laboratory are the same chemical compounds and work
equally well in the body. Contrary to claims in the health-food literature, “natural”
vitamins isolated from foods are, for the most part, no more healthful than those
synthesized in a laboratory, but there are exceptions. Vitamin E is much more potent
in its natural form. In contrast, synthetic folic acid, the form of the vitamin added
to ready-to-eat breakfast cereals and flour, is 1.7 times more potent than the natural
vitamin form.
megadose Intake of a nutrient beyond
estimates of needs to prevent a deficiency or
what would be found in a balanced diet; two
to 10 times human needs is a starting point
for such a dosage.
Absorption and Storage of Vitamins in the Body
The fat-soluble vitamins A, D, E, and K are absorbed along with dietary fat. These vitamins then travel with dietary fats as part of chylomicrons through the bloodstream
to reach body cells. Special carriers in the bloodstream help distribute some of these
vitamins. Fat-soluble vitamins are stored mostly in the liver and fatty tissues.
When fat absorption is efficient, about 40% to 90% of the fat-soluble vitamin is absorbed. Anything that interferes with normal digestion and absorption of fats, however,
also interferes with fat-soluble vitamin absorption. For example, people with cystic fibrosis, a disease that often hampers fat absorption, may develop deficiencies of fat-soluble
vitamins. Some medications, such as the weight-loss drug orlistat (Xenical), discussed in
Chapter 7, also interfere with fat absorption. Unabsorbed fat carries these vitamins to the
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bioavailability The degree to which an
ingested nutrient is absorbed and thus is
available to the body.
large intestine, where they are excreted in the feces. People with such conditions are especially susceptible to vitamin K deficiency because body stores of vitamin K are lower than
those of the other fat-soluble vitamins. Vitamin supplements, taken under a physician’s
guidance, are part of the treatment for preventing a vitamin deficiency associated with
fat malabsorption. Finally, people who use mineral oil as a laxative at mealtimes risk
fat-soluble vitamin deficiencies. The intestine does not absorb mineral oil, so fat-soluble
vitamins are eliminated with the mineral oil in the feces.
Water-soluble vitamins are handled much differently than fat-soluble vitamins. After
being ingested, the B vitamins are first broken down from their active coenzyme forms
into free vitamins in the stomach and small intestine. The vitamins are then absorbed,
primarily in the small intestine. Typically, about 50% to 90% of the B vitamins in the
diet are absorbed, which means they have relatively high bioavailability. Water-soluble
vitamins are transported to the liver via the portal vein and are distributed to body tissues. Once inside cells, the active coenzyme forms are resynthesized. There is no need to
consume the coenzyme forms. Some vitamins are sold in their coenzyme forms but these
are broken down during digestion and we activate them when needed.
Except for vitamin K, the fat-soluble vitamins are not readily excreted from the
body. In contrast, excesses of the water-soluble vitamins are rapidly lost from the
body, partly because the water in cells dissolves these vitamins and excretes them out
of the body via the kidneys. Water-soluble vitamins B-6 and B-12 are exceptions; these
are stored much more readily than the other water-soluble vitamins.
The limited storage of many vitamins dictates that they should be consumed in the
diet daily, although an occasional lapse in the intake of even water-soluble vitamins
causes no harm. Symptoms of a vitamin deficiency occur only when that vitamin is
lacking in the diet and the body stores are essentially exhausted. For example, an average person must consume no thiamin for 10 days or no vitamin C for 20 to 40 days
before developing the first symptoms of deficiency of these vitamins.
Vitamin Toxicity
Intakes in excess of daily needs for the water-soluble vitamins are rapidly lost from the
body because the kidneys efficiently filter the excess from the blood and excrete these compounds in urine. Notable exceptions are vitamin B-6 and vitamin B-12, stored in the liver.
Although they are water-soluble, these two B vitamins may accumulate to toxic levels.
In contrast to the water-soluble vitamins, fat-soluble vitamins are not readily excreted, so some can easily accumulate in the body and cause toxic effects. Although a
toxic effect from an excessive intake of any vitamin is theoretically possible, toxicity
of the fat-soluble vitamin A is the most frequently observed. With long-term intake,
Vitamin A causes toxicity in as little as two times human need. Vitamin E and the
water-soluble vitamins niacin, vitamin B-6, and vitamin C can also cause toxic effects,
but only when consumed in large amounts (15 to 100 times human needs or more).
vvitamins are unlikely to cause toxic effects unless taken in supplement (pill) form.
Some people believe that consuming vitamins far in excess of their needs provides them
with extra energy, protection from disease, and prolonged youth. They seem to think that
if a little is good, then more must be better. A “one-a-day” type of multivitamin and mineral supplement usually contains less than two times the Daily Values of the components,
so daily use of these products is unlikely to cause toxic effects in men and nonpregnant
women. But consuming many vitamin pills, especially potent sources of vitamin A, can
cause problems. Today, concentrated vitamin A supplements are widely available in grocery, drug, and health-food stores and pose risks for toxicity when used inappropriately.
Preservation of Vitamins in Foods
Good sources of vitamins can be found in all food groups, especially fruits and vegetables (Overview Figure 2). Substantial amounts of vitamins can be lost from the time
a fruit or vegetable is picked until it is eaten. The water-soluble vitamins, particularly
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Overview of the Micronutrients 287 MyPyramid:
Sources of Vitamins
and Choline
Grains
• Thiamin
• Riboflavin
• Niacin
• Folic acid
Vegetables
• Vitamin A
• Vitamin K
• Folate
• Vitamin C
Fruits
• Vitamin A
• Vitamin C
Oils
• Vitamin E
Milk
• Vitamin D
• Riboflavin
• Vitamin B-12
• Choline
overview figure 2 c Certain
groups of MyPyramid are especially
rich sources of various vitamins and
choline. This is true for those listed.
Each may be also found in other
groups in the pyramid but in lower
amounts. Pantothenic acid is also
present in moderate amounts in many
groups.
Meat & Beans
• Thiamin
• Riboflavin
• Niacin
• Biotin
• Vitamin B-6
• Vitamin B-12
• Choline
thiamin, vitamin C, and folate, can be destroyed with improper storage and excessive
cooking. Heat, light, exposure to the air, cooking in water, and alkalinity are factors
that can destroy vitamins. The sooner a food is eaten after harvest, the less chance of
nutrient loss.
Frozen vegetables and fruits are often as nutrient-rich as freshly picked ones because fruits and vegetables are often frozen immediately after harvesting. As part of
the freezing process, vegetables are quickly blanched in boiling water. This destroys
the enzymes that would otherwise degrade the vitamins. If a food is not eaten within
a few days, freezing is the best preservation method to retain nutrients.
Minerals: An Overview
Whereas vitamins are compounds consisting of many elements (e.g., carbon, oxygen,
and hydrogen), minerals are individual chemical elements. The mineral content of
foods is sometimes called “ash” because it is all that remains after the whole food has
been destroyed by high temperatures or chemical degradation. In humans, minerals
make up about 4% of adult body weight (Overview Figure 3). A mineral is essential
for humans if a dietary inadequacy results in a physiological or structural abnormality, and its addition to the diet prevents such illness or reinstates normal health. Sixteen minerals are known to be essential in the diet.
Minerals are categorized based on the amount we need per day. Recall from Chapter 1 that if we require greater than 100 milligrams (1/50 of a teaspoon) of a mineral
per day, it is considered a major mineral (Overview Table 3). These include calcium,
phosphorus, magnesium, sulfur, sodium, potassium, and chloride. Trace minerals
are required at levels less than 100 milligrams per day (Overview Table 4). Nine essential trace minerals (iron, zinc, copper, iodine, selenium, molybdenum, fluoride,
manganese, and chromium) have been identified for humans. There are several additional trace minerals (sometimes called ultratrace minerals) found in the human
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major mineral Vital to health, a mineral
required in the diet in amounts greater than
100 milligrams per day.
trace mineral Vital to health, a mineral
required in the diet in amounts less than 100
milligrams per day.
ultratrace mineral A mineral present
in the human diet in trace amounts but
that has not been shown to be essential to
human health.
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overview figure 3 c Approximate
1200
1200
1100
Some trace minerals
Major minerals
1000
Grams in Human Body
amounts of various minerals present in the
average human body. Other trace minerals
of nutritional importance not listed include
chromium, fluoride, molybdenum, selenium,
and zinc.
900
800
700
650
600
500
400
300
100
100
ide
er
pp
Co
ese
an
0.03
Iod
0.12
0.16
ng
esi
gn
10
n
um
ide
Ma
Ch
lor
m
diu
So
r
lfu
Su
m
siu
tas
Po
ho
osp
Ph
Ca
lciu
m
rus
30
Iro
180
100
Ma
200
200
Minerals
body, but many of them have no known requirements. These include arsenic, boron,
nickel, silicon, and vanadium.
Absorption and Storage of Minerals in the Body
oxalic acid (oxalate) An organic acid
found in spinach, rhubarb, and other leafy
green vegetables that can depress the absorption of certain minerals present in the food,
such as calcium.
phytic acid (phytate) A constituent of
plant fibers that binds positive ions to its
multiple phosphate groups.
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Foods offer us a plentiful supply of many minerals, but the ability of our bodies to
absorb and use them varies. The bioavailability of minerals depends on many factors,
including many nonmineral components of foods. Age, gender, genetic variables, nutritional status, and diet will affect mineral absorption and bioavailability. Numerous
prescription drugs also adversely affect mineral absorption. The mineral content listed
in a food composition table for the amount of a mineral in a food is a starting point
for estimating the contribution the food will make to our mineral needs.
Components of fiber, such as phytic acid (phytate) and oxalic acid (oxalate), can
limit absorption of some minerals by binding to them. Spinach, for example, contains
plenty of calcium, but only about 5% (compared to the typical 25% bioavailability of
calcium from foods) of it can be absorbed because of the vegetable’s high concentration of oxalic acid, which binds calcium. High-fiber diets—particularly those in excess
of current recommendations of 25 (adult women) to 38 (adult men) grams of fiber
per day—can decrease the absorption of iron, zinc, and possibly other minerals.
Many minerals, such as magnesium, calcium, iron, and copper, are of similar sizes
and electrical charges. Having similar sizes and the same electrical charge causes these
minerals to compete with each other for absorption, and therefore they affect each
other’s bioavailabilty. An excess of one mineral decreases the absorption and metabolism of other minerals. For example, a large intake of zinc decreases copper absorption. Therefore, people should avoid taking individual mineral supplements unless a
dietary deficiency or medical condition specifically warrants it. Food sources, however,
pose little risk for these mineral interactions, giving us another reason to emphasize
foods in meeting nutrient needs.
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Overview of the Micronutrients 289 OVERVIEW Table 3 Summary of the Major Minerals
Mineral
Major Functions
RDA, or
Adequate
Intake
Dietary Sources
Deficiency
Symptoms
Toxicity
Symptoms
Sodium
• Major positive ion Age 19–50 years:
• Table salt
• Muscle cramps
• Contributes to of the extracellular 1500 milligrams
• Processed foods hypertension in fluid
Age 51–70 years: • Condiments susceptible • Aids nerve impulse 1300 milligrams
• Sauces individuals transmission
Age > 70 years • Soups
• Increases • Water balance
1200 milligrams
• Chips calcium loss in urine
• Upper Level is 2300 milligrams
Potassium
• Major positive ion 4700 milligrams
of intracellular fluid
• Aids nerve impulse transmission
• Water balance
• Spinach
• Irregular heart beat
• Slowing of the • Squash
• Loss of appetite heartbeat, as • Bananas
• Muscle cramps seen in kidney • Orange juice failure • Milk • Meat • Legumes • Whole grains
Chloride
• Major negative ion 2300 milligrams
• Table salt
• Convulsions in
• Linked to of extracellular • Some infants hypertension in fluid vegetables susceptible • Participates in acid • Processed people when production in foods combined with stomach sodium • Aids nerve impulse • Upper Level is transmission 3600 milligrams • Water balance
Calcium
• Bone and tooth Age 9–18 years:
• Dairy products
• Increased risk
• May cause kidney structure
1300 milligrams
• Canned fish of osteoporosis stones and other • Blood clotting
• Leafy problems in • Aids in nerve impulse Age > 18 years:
vegetables susceptible people transmission
1000–1200 milligrams • Tofu
• Upper Level is • Muscle contractions
• Fortified orange 2500 milligrams • Other cell functions juice (and other fortified foods)
• Dairy products
• Possibility of
• Impairs bone Phosphorus • Major ion of Age 9–18 years: intracellular fluid
1250 milligrams
• Processed foods poor bone health in people • Bone and tooth • Fish maintenance with kidney failure strength
• Soft drinks
• Poor bone • Part of various Age > 18 years:
• Bakery mineralization if metabolic 700 milligrams
products calcium intakes compounds
• Meats are low • Acid/base balance
• Upper Level is 3 to 4 grams
Magnesium • Bone formation
Men:
• Wheat bran
• Weakness
• Causes diarrhea and • Aids enzyme 400–420 milligrams
• Green
• Muscle pain weakness in people function vegetables
• Poor heart with kidney failure • Aids nerve and Women: • Nuts function
• Upper Level is heart function
310–320 milligrams
• Chocolate 350 milligrams, but • Legumes refers to nonfood
sources (e.g.,
supplements) only
Sulfur
• Part of vitamins and amino acids • Aids in drug detoxification • Acid/base balance
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OVERVIEW Table 4 A Summary of Key Trace Minerals
Mineral
Major Functions
RDA, or
Adequate
Intake
Dietary Sources
Deficiency
Symptoms
Toxicity
Symptoms
Iron
• Components of Men:
• Meats
• Fatigue
• Liver and heart hemoglobin and 8 milligrams
• Seafood
• Anemia damage other key compounds • Broccoli
• Low blood (extreme used in respiration
Premenopausal
• Peas hemoglobin cases) • Immune function
Women:
• Bran values
• GI upset • Cognitive 18 milligrams
• Enriched • Upper Level is development breads 45 milligrams
Zinc
• Required for nearly Men:
• Seafood
• Skin rash
• Reduced copper 200 enzymes
11 milligrams
• Meats
• Diarrhea absorption • Growth
• Greens
• Decreased • Diarrhea • Immunity
Women:
• Whole grains appetite and
• Cramps • Alcohol metabolism
8 milligrams sense of taste
• Depressed immune • Sexual development
• Hair loss function • Reproduction
• Poor growth and
• Upper Level is • Antioxidant protection development 40 milligrams • Poor wound healing
Selenium
• Part of an 55 micrograms
• Meats
• Muscle pain
• Nausea antioxidant system
• Eggs
• Weakness
• Vomiting • Fish
• Form of heart
• Hair loss • Seafood disease
• Weakness • Whole grains
• Liver disease • Upper Level is 400 micrograms
Iodide
• Component of 150 micrograms • Iodized salt
• Goiter
• Inhibition of thyroid hormones
• White bread
• Mental thyroid gland • Saltwater fish retardation function • Dairy products
• Poor growth in infancy • Upper Level is when mother is iodide 1.1 milligrams deficient during pregnancy
Copper
• Aids in iron 900 micrograms
metabolism
• Works with many antioxidant enzymes
• Involved with enzymes
of protein metabolism and hormone synthesis
• Liver
• Anemia
• Vomiting • Cocoa
• Low white • Nervous • Beans blood cell count system • Nuts
• Poor growth disorders • Whole grains
• Upper Level is • Dried fruits 8–10 milligrams Fluoride
• Increases Men:
• Fluoridated water
• Increased risk • Stomach upset resistance of tooth 3.8 milligrams
• Toothpaste of dental caries
• Mottling (staining) of enamel to dental • Tea teeth during development caries
Women:
• Seaweed
• Bone pain 3.1 milligrams
• Dental treatments
• Upper Level is 10 milligrams for adults
Chromium
• Enhances insulin 25–35
action
micrograms
• Egg yolks
• High blood • Whole grains glucose after
• Pork eating
• Nuts
• Mushrooms • Beer
Caused by industrial contamination, not dietary excesses, so no Upper Level has been set Manganese • Cofactor of some 1.8–2.3
• Nuts
None observed in
• Nervous system enzymes, such as milligrams
• Oats
humans disorders those involved in • Beans
• Upper Level is carbohydrate • Tea 11 milligrams metabolism • Works with some antioxidant systems
Molybdenum • Aids in action of 45 micrograms
some enzymes
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• Beans
None observed in
• Poor growth in • Grains
healthy humans laboratory animals • Nuts
• Upper Level is 2 milligrams
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Overview of the Micronutrients 291 Several beneficial vitamin-mineral interactions occur during nutrient absorption
and metabolism. When consumed in conjunction with vitamin C, absorption of certain forms of iron—such as that in plant products—improves. The active form of
vitamin D hormone improves calcium absorption. Many vitamins require specific
minerals to act as components in their structure and function. For example, the thiamin coenzyme requires magnesium or manganese to efficiently function.
The average North American diet derives minerals from both plant and animal
sources. Overall, minerals from animal products are better absorbed than those
from plants because binders such as fiber are not present to hinder absorption.
The mineral content of plants greatly depends on mineral concentrations of the
soil in which they are grown. Vegans must be aware of the potentially poor mineral
content of some plant foods and choose some concentrated sources of minerals.
Soil conditions have less of an influence on the mineral content of animal products
because livestock usually consume a variety of plant products grown from soils of
differing mineral contents.
Like vitamins, the majority of the minerals are absorbed in the small intestine.
Minor amounts may be absorbed in the stomach, and some sodium and potassium is
absorbed in the large intestine. After minerals are absorbed, some travel freely in the
bloodstream, but many are carried by specific transport proteins to their site of action
or storage. Calcium is one example of a mineral that can travel as an ion in the blood
or bound to a blood protein called albumin. Iron, on the other hand, has damaging
effects in its unbound form, so it is transported bound to proteins, such as transferrin. Minerals are stored in various tissues throughout the body. Some minerals must
remain in the bloodstream to maintain fluid balance and supply body functions.
Others, such as calcium, phosphorus, magnesium, and fluoride, are stored mainly in
bones. Iron, copper, zinc, and many trace minerals are stored in the liver. Still others
are stored in muscle tissue, organs, or glands.
Mineral Toxicities
An excessive mineral intake, especially of trace minerals such as iron and copper, can have toxic results. For many trace minerals, the gap between just enough
and too much is small. Taking minerals as supplements poses the biggest threat
for mineral toxicity, whereas food sources are unlikely culprits. Mineral supplements exceeding current standards for mineral needs—especially those that supply
more than 100% of the Daily Values on supplement labels—should be taken only
under a physician’s supervision. The Daily Values are for the most part higher than
our current standards (e.g., Recommended Dietary Allowances [RDA]) for mineral
needs. Without close monitoring, doses of minerals should not exceed any Upper
Level set on a long-term basis.
The potential for toxicity is not the only reason to carefully consider the use of
mineral supplements. Harmful interactions with other nutrients are possible. Also,
contamination of mineral supplements—with lead, for example—is a possibility. Use
of brands approved by the United States Pharmacopeia (USP) lessens this risk. Even
with the best intentions, people may harm themselves using mineral supplements.
Preservation of Minerals in Foods
Minerals are found in plant and animal foods (Overview Figure 4), but as you previously read, the bioavailability of minerals varies widely. Minerals are not typically lost
from animal sources during processing, storage, or cooking, but for plant sources,
significant amounts may be lost during food processing. When grains are refined, the
final products have lost the majority of their vitamin E, many B vitamins, and trace
minerals. The more refined a plant food, as in the case of white flour, the lower its
mineral content. During the enrichment of refined grain products, iron is the only
mineral added, whereas the selenium, zinc, copper, and other minerals lost during
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292 Contemporary Nutrition: A Functional Approach www.mhhe.com/wardlawcontfa1
MyPyramid:
Sources of Minerals
Grains
• Sodium
chloride
• Calcium
(fortified
products)
• Phosphorus
• Magnesium
• Iron
• Zinc
• Copper
• Selenium
• Chromium
Vegetables
• Potassium
• Magnesium
Fruits
• Potassium
• Boron
Oils
• None
Milk
• Calcium
• Phosphorus
• Zinc
Meat & Beans
• Sodium
chloride
(processed
foods)
• Potassium
• Phosphorus
• Magnesium
• Selenium
• Iron
• Zinc
• Copper
overview figure 4 c Certain groups of MyPyramid are especially rich sources of various minerals. This is
true for the minerals listed. Each mineral may also be found in other groups, but in lower amounts. Other trace
minerals are also present in moderate amounts in many groups. With regard to the grains group, whole-grain
varieties are the richest sources of most trace minerals listed.
refinement are not replaced. Following the recommendation of the 2005 Dietary
Guidelines for Americans to “make half your grains whole” will effectively preserve
the mineral content of foods.
The Functional Roles of Micronutrients
The next four chapters will explore the vitamins and minerals from a functional perspective. The micronutrients will be grouped and discussed as they apply to various
metabolic roles in the body. Keep in mind that each vitamin and mineral has multiple
roles in metabolism. For example, calcium, best known for its role in bone formation,
is also crucial for the transmission of nerve impulses through the body and plays a
role in blood clotting. Vitamin C contributes to cellular antioxidant function, bone
health, and metabolism of proteins. At all levels – cellular, tissue, organ, and whole
body – vitamins and minerals clearly play important and interrelated roles in maintaining healthy body functions.
Chapter 8 focuses on the roles of the micronutrients in fluid and electrolyte balance. Water balance requires sodium, potassium, chloride, and phosphorus. Levels of
these minerals in the blood are tightly regulated by the body and imbalances can have
dire consequences. In addition to maintaining the delicate balance between intracel-
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Overview of the Micronutrients 293 lular and extracellular water, these minerals participate in the transmission of nerve
impulses and acid-base balance.
Chapter 9 will enhance your understanding of the body’s antioxidant systems and
how various vitamins and minerals take part in protecting tissues from oxidative damage. Vitamin E, vitamin C, vitamin A and its precursor carotenoids, as well as selenium
are discussed in this chapter. In addition, the roles of beneficial plant chemicals in
protection of human health will be explored.
Before moving ahead in your study of vitamins and minerals as they participate in
antioxidant systems (and energy metabolism, discussed in Chapter 11), it is important
to understand how enzymes work.
Enzymes are catalysts for biochemical reactions in living organisms. A catalyst is a
compound that speeds the rate of a reaction but is not altered by the reaction. Most of
the chemical reactions in the body would not occur, or would occur only at very slow
rates, in the absence of catalysts. Enzymes allow for the breakdown of carbohydrates,
lipids, and proteins to generate energy. They also catalyze synthetic reactions, such as
the assembly of triglycerides for storage in adipose tissue. Enzymes are crucial players
in antioxidant reactions, which neutralize damaging free radicals in the body. Beyond
these few roles, thousands of other enzymes have been identified and studied.
Typically, enzymes are made of proteins, but many such proteins require the aid
of another compound (a cofactor, such as a coenzyme) for biological activity (Overview Figure 5). Frequently, the assisting compound is a vitamin or mineral, such as
copper or selenium. In some reactions, numerous vitamins and minerals are required
as coenzymes. Requirements for an enzyme and its coenzymes are specific, with little
or no enzymatic activity observed if another coenzyme is substituted for the required
one. Minerals are required for activation of about 30% of coenzyme all known enzymes.
In Chapter 10, you will learn how micronutrients are vital to bone health. When we
think of bone, we often imagine the hard, lifeless architecture of a skeleton hanging in
the back of our high school science classroom. However, bone is a living and dynamic
tissue that supports growth, houses nerves and blood vessels, produces blood cells,
and helps regulate blood levels of certain minerals. This chapter explores the roles of
calcium, phosphorus, vitamin D, vitamin K, magnesium, fluoride, and some other
vitamins and ultratrace minerals in bone health.
Chapter 11 delves into the roles of vitamins and minerals in energy metabolism
and blood health. Although vitamins and minerals yield no energy to the body, they
often participate as coenzymes in energy-yielding reactions. All of the B vitamins are
involved in metabolism of the macronutrients, as are many trace minerals. Blood
health encompasses immune function; clotting ability; and transport of oxygen, nutrients, and waste products. Blood health is influenced by vitamin K, iron, zinc, copper, and various B vitamins.
Micronutrients are vital to every aspect of human health. Although requirements
for vitamins and minerals are small, depriving the body of any one of these important
dietary factors can be debilitating or deadly. For most healthy children and adults,
foods are safe, effective, and enjoyable sources of vitamins and minerals, although
dietary supplements may be useful under some circumstances. As you study the next
four chapters, prepare to be amazed by the intricate interplay of micronutrients and
human health.
Inactive
enzyme
Vitamin
coenzyme
Active
enzyme
overview figure 5 c Coenzymes,
such as those formed from B vitamins, aid
in the function of various enzymes. Without
the coenzyme, the enzyme cannot function,
and deficiency symptoms associated with the
missing vitamin eventually appear. Healthfood stores sell the coenzyme forms of some
vitamins. These more expensive forms of vitamins are unnecessary. The body makes all the
coenzymes it needs from vitamin precursors.
enzyme A compound that speeds the rate
of a chemical reaction but is not altered by
the reaction. Almost all enzymes are proteins
(some are made of genetic material).
cofactor A substance that binds to a specific region on a protein, such as an enzyme,
and is necessary for the protein’s function.
coenzyme A compound (frequently a
.
vitamin or mineral) that combines with an
inactive enzyme to form a catalytically active
form. In this manner, coenzymes aid in enzyme function.
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