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Calcium
is essential for many body functions,
including regulation of the heartbeat,
conduction of nerve impulses,
stimulation of hormone secretions and
clotting of blood, as well as for
building and maintaining a healthy
skeleton.
Calcium
is a mineral found in many foods and
adequate calcium intake is important
because the human body cannot produce
calcium. Even after reaching full
skeletal growth, adequate calcium intake
is important because the body loses
calcium every day through shed skin,
nails, hair, and sweat as well as
through urine and feces. This lost
calcium must be replaced daily through
the diet. When the diet does not contain
enough calcium to perform these
activities, calcium is taken from the
bones, the storage area for calcium.
The National Academy of Sciences and the
National Osteoporosis Foundation
recommend daily calcium intakes of
1000-1200 mg/day for adult men and
women. According to experts, food is the
best source of calcium; however, most
Americans do not have enough calcium in
their diets. Fortunately,
calcium-fortified foods and calcium
supplements can fill the gap, ensuring
that the daily calcium requirement is
met. The amount needed from a supplement
depends on how much calcium is consumed
from food sources.
Calcium exists in nature only in
combination with other substances called
compounds. Several different calcium
compounds are used in supplements,
including calcium carbonate, calcium
phosphate and calcium citrate. These
compounds contain different amounts of
elemental calcium, which is the actual
amount of calcium in the supplement. It
is important to read the label carefully
to determine how much elemental calcium
is in the supplement and how many doses
or pills to take.
Calcium supplements are available
without a prescription in a wide range
of preparations and strengths, which can
make selecting one a confusing
experience. Many people ask which
calcium supplement they should take; the
"best" supplement is the one that meets
an individual’s needs based on
tolerance, convenience, cost and
availability. In choosing a calcium
supplement, the following are important
considerations:
Purity
Choose calcium supplements that are
known brand names with proven
reliability. Look for labels that state
"purified" or have the USP (United
States Pharmacopeia) symbol. Since
applying for the USP symbol is
voluntary, however, many fine products
may not display this symbol. Avoid
calcium from unrefined oyster shell,
bone meal or dolomite without the USP,
as these historically have contained
higher lead levels or other toxic
metals.
Absorbability
Most brand name calcium products are
absorbed easily in the body. If the
product information does not state that
it is absorbable, how well a tablet
dissolves can be determined by placing
it in a small amount of warm water for
30 minutes, stirring it occasionally. If
it hasn’t dissolved within this time it
probably will not dissolve in the
stomach. Chewable and liquid calcium
supplements dissolve well because they
are broken down before they enter the
stomach.
Calcium, whether from the diet or
supplements, is absorbed best by the
body when it is taken several times a
day in amounts of 500 mg or less, but
taking it all at once is better than not
taking it at all. Calcium carbonate is
absorbed best when taken with food.
Calcium citrate can be taken any time.
Tolerance
While calcium supplements generally are
a satisfactory option for many people,
certain preparations may cause side
effects, such as gas or constipation, in
some individuals. If simple measures
such as increased fluids and fiber
intake do not solve the problem, another
form of calcium should be tried. Also,
it is important to increase supplement
intake gradually; take 500 mg a day for
a week, then add more calcium slowly.
Calcium Interactions
It is important to talk with a physician
or pharmacist about possible
interactions between prescription or
over-the-counter medications and calcium
supplements. For example, calcium
supplements also may reduce the
absorption of the antibiotic
tetracycline. Calcium also interferes
with iron absorption, so a calcium
supplement should not be taken at the
same time as an iron supplement. The
exception to this is when the iron
supplement is taken with vitamin C or
calcium citrate. Any medication to be
taken on an empty stomach should not be
taken with calcium supplements.
Combination Products
Calcium supplements are available in a
dazzling array of combinations with
vitamins and other minerals. While
vitamin D is necessary for the
absorption of calcium, it is not
necessary that it be in the calcium
supplement (see winter 1998 issue of
Osteoporosis Report for information on
vitamin D). Minerals such as magnesium
and phosphorus also are important, but
usually are obtained through food or
multivitamins. Most experts recommend
that nutrients come from a balanced
diet, with multivitamins used to
supplement dietary deficiencies.
Most published studies show that low
calcium intake is associated with low
bone mass, rapid bone loss and high
fracture rates. Adequate calcium intake
will help ensure that calcium deficiency
is not contributing to a weakening of
the skeleton; however, this is only one
of the steps necessary for bone health.
A high calcium intake will not protect a
person against bone loss caused by
estrogen deficiency, physical
inactivity, smoking, alcohol abuse or
various medical disorders or treatments.
This Strategy for Osteoporosis appeared
in the Spring 1999 Issue of NOF's
Quarterly Member Newsletter,
Osteoporosis Report. NOF thanks Murray
J. Favus, M.D., University of Chicago,
for his assistance in reviewing this
article.
Individual Members of NOF, receive our
quarterly newsletter, Osteoporosis
Report, and a copy of our newly revised,
70-page handbook, Boning Up on
Osteoporosis.
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