demand for calcium supplements is reflected
by retail sales data. In 1993, calcium supplements
accounted for 6.7% of total supplement sales
or $245 million a year in the US. Between 1994
and 1999, sales for calcium supplements increased
60%. Reasons why individuals take calcium supplements
are varied and include: concerns about the adequacy
of the calcium content of their diets; perceived
or actual milk protein allergy/lactose intolerance;
and a desire to provide insurance against calcium
deficiency or to treat or prevent disease.
is 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
shedding 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.
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.
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.
to a recent review of calcium preparations,
there are at least a dozen common calcium preparations
and hundreds of different formulations available.
Calcium carbonate is the most common preparation;
some others include tricalcium phosphate, dicalcium
phosphate, bone meal, calcium citrate-malate,
oyster shell, calcium lactate, and calcium gluconate.
These calcium preparations differ in a variety
of ways. Calcium carbonate has the highest concentration
of calcium by weight (40%), whereas calcium
citrate has 21% calcium and calcium phosphate
has 8% calcium by weight.
calcium carbonate has the highest concentration
of calcium by weight, this form of calcium is
relatively insoluble, especially at a neutral
pH. In contrast, calcium citrate, although containing
about half as much calcium by weight, is a more
soluble form of calcium. Because calcium citrate
does not require gastric acid for absorption,
it is a better choice for patients with achlorhydria
(i.e., limited gastric acid production).
addition to the amount (dosage) of calcium in
various supplements, the solubility and absorption
of calcium must be considered. Prior to
absorption, calcium preparations must dissociate
into elemental calcium. The more soluble a calcium
supplement product is in vitro (i.e., measured
by the ability to dissolve in 6 ounces of vinegar
within 30 minutes), the more soluble the calcium
preparation is in the body.
dosage and solubility can influence the bioavailability
of calcium from calcium supplements, the timing
of intake and meal conditions also are important.
Calcium from supplements appears to be more
efficiently absorbed when consumed in divided
doses, each containing less than 200 mg of elemental
calcium. The NIH Consensus Conference recommends
consuming calcium supplements between meals
to increase calcium bioavailabilty.
long-term safety of consuming large doses of
single nutrients including calcium is of concern.
Although calcium intakes up to 2,000 mg/day
appear to be safe for most individuals, potential
adverse effects can occur as a result of chronic
high intakes or intakes of specific calcium
preparations. Potential adverse effects include
gastrointestinal problems such as constipation.
Certain preparations of calcium (e.g., bone
meal, dolomite) may contain contaminants such
as lead, aluminum, arsenic, mercury, and cadmium.
Significant amounts were identified in calcium
carbonate supplements labeled oyster shell or
natural source. Chronic intake of these supplements
may pose an unnecessary risk. Most commercial
calcium preparations are tested for heavy metal
intakes of calcium supplements may interfere
with the absorption of other nutrients such
as iron and zinc. Intake of calcium supplements
also may interfere with the absorption of concurrently
consumed medications, and vice versa. Other
potential adverse effects of chronic intakes
of high doses of calcium include milk-alkali
syndrome (ectopic calcium deposition), hypervitaminosis
D (i.e., in the case of supplements containing
calcium and vitamin D), and possible hypercalciuria
leading to kidney stone formation. However,
recent studies indicate that increased intake
of calcium does not increase risk of kidney
stones. Moreover, restricting dietary calcium
may increase urinary excretion of oxalate which
in turn increases risk of kidney stones.
certain individuals who cannot meet their calcium
needs from foods, calcium supplements are warranted.
However as reviewed above, a number of factors
influence the choice of calcium preparation.
Individuals who need calcium supplements should
choose one that contains a relatively high percentage
of elemental calcium by weight, disintegrates
readily, provides a form of calcium that is
bioavailable and inexpensive, is manufactured
by a reputable pharmaceutical company, and is
free of toxicants. In general, absorption of
calcium is most efficient when the supplement
is consumed in doses of 200 mg or less. Intake
of calcium supplements with vitamin D should
be limited because of the risk for vitamin D
products are generally absorbed easily in the
body. Tablets and pills are not the best solution
for an added intake of calcium, as they vary
in their ability to be fully digested. 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 hasnít dissolved
within this time it probably will not dissolve
in the stomach.
calcium supplements dissolve well because they
are broken down before they enter the stomach.
are some "high tech" calcium supplements available
that must be mixed in a liquid, than drunk.
These deliver nearly 100% of their available
mineral solution as they are in a nearly "pre-digested"
whether from the diet or supplements, is absorbed
best by the body when it is taken several times
a day in amounts of 200 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
calcium supplements generally are a satisfactory
option for many people, certain preparations
may cause side effects, such as gas or
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 200 mg a day
for a week, then add more calcium slowly.
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.
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. 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.
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.