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 indi-
viduals 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 chemi-
cally binding to the mineral. In addition, excess intake
of one mineral can influence the absorption and
metabolismof other minerals. For example, the pres-
ence of a large amount ofzincin the diet decreases the
absorption ofironand copper. On the other hand, the
presence ofvitaminsin a meal enhances the absorp-
tion of minerals in the meal. For example,vitamin C
improves iron absorption, andvitamin Daids in the
absorption of calcium, phosphorous, and magnesium.
In general, minerals from animal sources are
absorbed better than those from plant sources as min-
erals 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 nec-
essary to include foods rich in minerals and absorp-
tion-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 Daily
Allowances(RDAs) or Adequate Intakes(AIs) for nor-
mal healthy people.
The Food and Nutrition Board currently recom-
mends 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 supple-
ments. Because of the increased need for iron in
women of childbearing age, as well as the many neg-
ative 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 inju-
ries, 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, magne-
sium, iron, zinc, copper, andselenium) and tolerableTrace minerals that can be found in commercial
preparations of colloidal mineralsAluminum Molybdenum
Antimony Neodymium
Arsenic Nickel
Barium Niobium
Beryllium Nitrogen
Bismuth Osmium
Boron Oxygen
Bromine Phosphorus
Cadmium Platinum
Calcium Potassium
Carbon Praseodymium
Cerium Ralladium
Cesium Rhodium
Chloride Rubidium
Chromium Ruthenium
Cobalt Samarium
Copper Scandium
Dyprosium Selenium
Erbium Silicon
Europium Silver
Fluoride Sodium
Gadolinium Strontium
Gallium Sulfur
Germanium Tantalum
Gold Tellurium
Hafnium Terbium
Holmium Thalium
Hydrogen Thenium
Indium Thorium
Iodine Thulim
Iridium Tin
Iron Titanium
Lanthanum Tungsten
Lead Vanadium
Lithium Ytterbium
Lutetium Yttrium
Magnesium Zinc
Manganese Zirconium
MercuryColloidal mineral supplements are usually liquid extracts of
minerals mainly derived from humic shale deposits or from
aluminosilicate-containing clays.(Illustration by GGS Informa-
tion Services/Thomson Gale.)
Minerals