Minerals are inorganic elements that originate in the earth and cannot be made in the body. They play important
roles in various bodily functions and are necessary to sustain life and maintain optimal health, and thus are essential
nutrients. Most of the minerals in the human diet come directly from plants and water, or indirectly from animal foods.
However, the mineral content of water and plant foods varies geographically because of variations in the mineral
content of soil from region to region.
The amount of minerals present in the body, and their metabolic roles, varies considerably. Minerals provide
structure to bones and teeth and participate in energy production, the building of protein, blood formation, and
several other metabolic processes. Minerals are categorized into major and trace minerals, depending on the
amount needed per day. Major minerals are those that are required in the amounts of 100 mg (milligrams) or more,
while trace minerals are required in amounts less than 100 mg per day. The terms major and trace, however, do not
reflect the importance of a mineral in maintaining health, as a deficiency of either can be harmful.
Some body processes require several minerals to work together. For example, calcium, magnesium, and
phosphorus are all important for the formation and maintenance of healthy bones. Some minerals compete with each
other for absorption, and they interact with other nutrients as well, which can affect their bioavailability.
Mineral Bioavailability
The degree to which the amount of an ingested nutrient is absorbed and available to the body is called
bioavailability. Mineral bioavailability depends on several factors. Higher absorption occurs among individuals who
are deficient in a mineral, while some elements in the diet (e.g., oxalic acid or oxalate in spinach) can decrease
mineral availability by chemically binding to the mineral. In addition, excess intake of one mineral can influence the
absorption and metabolism of other minerals. For example, the presence of a large amount of zinc in the diet
decreases the absorption of iron and copper. On the other hand, the presence of vitamins in a meal enhances the
absorption of minerals in the meal. For example, vitamin C improves iron absorption, and vitamin D aids in the
absorption of calcium, phosphorous, and magnesium.
In general, minerals from animal sources are absorbed better than those from plant sources as minerals are present
in forms that are readily absorbed and binders that inhibit absorption, such as phytates, are absent. Vegans (those
who restrict their diets to plant foods) need to be aware of the factors affecting mineral bioavailability. Careful meal
planning is necessary to include foods rich in minerals and absorption-enhancing factors.
Supplementation
It is generally recommended that people eat a well-balanced diet to meet their mineral requirements, while avoiding
deficiencies and chemical excesses or imbalances. However, supplements may be useful to meet dietary
requirements for some minerals when dietary patterns fall short of Recommended Dietary Allowances (RDAs) or
Adequate Intakes (AIs) for normal healthy people.
The Food and Nutrition Board currently recommends that supplements or fortified foods be used to obtain desirable
amounts of some nutrients, such as calcium and iron. The recommendations for calcium are higher than the average
intake in the United States. Women, who generally consume lower energy diets than men, and individuals who do
not consume dairy products can particularly benefit from calcium supplements. Because of the increased need for
iron in women of childbearing age, as well as the many negative consequences of iron-deficiency anemia, iron
supplementation is recommended for vulnerable groups in the United States, as well as in developing countries.
Mineral supplementation may also be appropriate for people with prolonged illnesses or extensive injuries, for those
undergoing surgery, or for those being treated for alcoholism. However, extra caution must be taken to avoid intakes
greater than the RDA or AI for specific nutrients because of problems related to nutrient excesses, imbalances, or
adverse interactions with medical treatments. Although toxic symptoms or adverse effects from excess
supplementation have been reported for various minerals (e.g., calcium, magnesium, iron, zinc, copper, and
selenium) and tolerable upper limits set, the amounts of nutrients in supplements are not regulated by the
Food and Drug Administration (FDA). Therefore, supplement users must be aware of the potential adverse effects
and choose supplements with moderate amounts of nutrients.
Major Minerals
The major minerals present in the body include sodium, potassium, chloride, calcium, magnesium, phosphorus, and
sulfur.
Functions.
The fluid balance in the body, vital for all life processes, is maintained largely by sodium, potassium, and chloride.
Fluid balance is regulated by charged sodium and chloride ions in the extracellular fluid (outside the cell) and
potassium in the intracellular fluid (inside the cell), and by some other electrolytes across cell membranes. Tight
control is critical for normal muscle contraction, nerve impulse transmission, heart function, and blood pressure.
Sodium plays an important role in the absorption of other nutrients, such as glucose, amino acids, and water.
Chloride is a component of hydrochloric acid, an important part of gastric juice (an acidic liquid secreted by glands in
the stomach lining) and aids in food digestion. Potassium and sodium act as cofactors for certain enzymes.
Calcium, magnesium, and phosphorus are known for their structural roles, as they are essential for the development
and maintenance of bones and teeth. They are also needed for maintaining cell membranes and connective tissue.
Several enzymes, hormones, and proteins that regulate energy and fat metabolism require calcium, magnesium
and/or phosphorus to become active. Calcium also aids in blood clotting. Sulfur is a key component of various
proteins and vitamins and participates in drug-detoxifying pathways in the body.
Disease prevention and treatment.
Sodium, chloride, and potassium are linked to high blood pressure (hypertension) due to their role in the body's fluid
balance. High salt or sodium chloride intake has been linked to cardiovascular disease as well. High potassium
intakes, on the other hand, have been associated with a lower risk of stroke, particularly in people with hypertension.
Research also suggests a preventive role for magnesium in hypertension and cardiovascular disease, as well as a
beneficial effect in the treatment of diabetes, osteoporosis, and migraine headaches.
Osteoporosis is a bone disorder in which bone strength is compromised, leading to an increased risk of fracture.
Along with other lifestyle factors, intake of calcium and vitamin D plays an important role in the maintenance of bone
health and the prevention and treatment of osteoporosis. Good calcium nutrition, along with low salt and high
potassium intake, has been linked to prevention of hypertension and kidney stones.
Deficiency.
Dietary deficiency is unlikely for most major minerals, except in starving people or those with protein-energy
malnutrition in developing countries, or people on poor diets for an extended period, such as those suffering from
alcoholism, anorexia nervosa, or bulimia. Most people in the world consume a lot of salt, and it is recommended that
they moderate their intake to prevent chronic diseases (high salt intake has been associated with an increased risk
of death from stroke and cardiovascular disease). However, certain conditions, such as severe or prolonged
vomiting or diarrhea, the use of diuretics, and some forms of kidney disease, lead to an increased loss of minerals,
particularly sodium, chloride, potassium, and magnesium. Calcium intakes tend to be lower in women and vegans
who do not consume dairy products. Elderly people with suboptimal diets are also at risk of mineral deficiencies
because of decreased absorption and increased excretion of minerals in the urine.
Toxicity.
Trace minerals can be toxic at higher intakes, especially for those minerals whose absorption is not regulated in the
body (e.g., selenium and iodine). Thus, it is important not to habitually exceed the recommended intake levels.
Although toxicity from dietary sources is unlikely, certain genetic disorders can make people vulnerable to overloads
from food or supplements. One such disorder, hereditary hemochromatosis, is characterized by iron deposition in
the liver and other tissues due to increased intestinal iron absorption over many years.
Chronic exposure to trace minerals through cooking or storage containers can result in overloads of iron, zinc, and
copper. Fluorosis, a discoloration of the teeth, has been reported in regions where the natural content of fluoride in
drinking water is high. Inhalation of manganese dust over long periods of time has been found to cause brain
damage among miners and steelworkers in many parts of the world.
In summary, minerals, both major and trace, play vital roles in human health, and care must be taken to obtain
adequate intakes from a wide variety of whole foods. The most common result of deficiencies is poor growth and
development in children. Minerals interact with each other and with other nutrients, and caution is required when
using supplements, as excess intake of one mineral can lead to the deficiency of another nutrient.
SEE ALSO ANEMIA; BIOAVAILABILITY; CALCIUM; DIETARY SUPPLEMENTS; OSTEOPOROSIS; VITAMINS,
FAT-SOLUBLE; VITAMINS, WATER-SOLUBLE.
Sunitha Jasti
Bibliography
Wardlaw, Gordon M. (1999). Perspectives in Nutrition, 4th edition. Boston: WCB McGraw-Hill.
Whitney, Eleanor N., and Rolfes, Sharon R. (1996). Understanding Nutrition, 7th edition. New York: West Publishing.