Calcium Forms, Bioavailability Subject of Industry Discussion
by
Kurt Schneider
Reprinted
by permission from Boston Mountain
Laboratories
Calcium
is returning to the forefront of the dietary supplement industry. Much of the
recent publicity has centered on coral calcium, including supplier claims of
higher absorptivity and bioavailability. Coral calcium can be considered 'young'
calcium carbonate ore, which is an economical, pure and widely available source
of calcium.
Calcium is a mineral
often taken for granted in our diets, usually consisting of a daily dose of a
multi-vitamin or a calcium supplement. Despite supplementation, osteoporosis--or
bone density loss--remains prevalent. The human body needs a source of calcium
that can be absorbed at a level effective in fighting osteoporosis. To do so,
there are many forms of calcium currently available, such as calcium carbonate,
calcium citrate, calcium gluconate, oyster shell, scallop shell, eggshell, milk
products and, the latest, coral calcium. While there has been much debate over
which type is best, it is clear that whatever form is taken, it needs to be
absorbed by the body to provide any benefit.
As calcium is ingested,
the acid in the stomach begins to break down the molecule into its atomic
components. In the case of calcium carbonate, the components are elemental
calcium and carbonic acid, which further breaks down into carbon dioxide. At
this point the calcium is in its ionic, or positively charged, state. In this
state, the calcium can pass through the intestinal tract, into the bloodstream,
and into the bones. It is this rate of calcium absorption, or bioavailability,
that determines how much of the ingested calcium actually can be used by the
body. The higher the bioavailability, the more calcium ions can travel into the
body. In addition, the faster the supplement can obtain this ionic state, the
faster it becomes available for absorption. Since time is critical, it is
important to ensure as much calcium is absorbed before it passes through the
body. Studies have shown that as long as the body absorbs enough calcium, the
rate of absorption is not indicative of the quality of the calcium. The
bioavailability or absorption and uptake of calcium are partly a function of pH.
Acidity favors absorption while alkalinity hinders absorption. An increase in
acidophilic flora (i.e., L. acidophilus)
in the intestine favors calcium absorption.1 With normal gastric
function, almost all calcium forms become soluble and bioavailable. Further,
studies have shown that solubility of calcium forms does not significantly
affect absorption.2 Calcium carbonate is not soluble in water; it is
soluble in acid and is well-absorbed in normal gastric function.
Levels of calcium in
various products also vary. Calcium percentages range from 9 percent for calcium
gluconate to nearly 40 percent for calcium carbonate.3 It would
appear that the higher starting level of calcium would provide better absorption
and bioavailability; this is not necessarily the case. As the supplement passes
through the body, studies have shown there is little difference in
bioavailability between all major types of calcium. When taken with meals,
calcium carbonate has been shown to be as or more absorbable (39%) as five other
forms of calcium, including calcium acetate (32%), calcium lactate (32%), milk
(31%), calcium citrate (30%) and calcium gluconate (27%).4
There are other factors
that play a role in how well the body absorbs calcium. "Nutrients in foods
interact with each other, and the absorption of any nutrient depends, in part,
upon the foods that are eaten with it and the nutrients and other substances
those foods contain," wrote Suzanne Havala, M.S., R.D., in the Vegetarian
Journal. "It also depends upon the body's need for the
particular nutrient. Our bodies can adapt to varying dietary conditions; when we
need more of many nutrients, the body may compensate and become more efficient
at absorbing them."5
Even similar forms of
calcium may come from different sources. For example, calcium carbonate can come
from a variety of fossilized deposit sources: limestone, precipitated limestone,
oyster shell, scallop shell, eggshell, fish bones and coral. According to
geologist Jose N. Peralta Villar, the age of the deposit is the only major
difference between the sources.6 "Some deposits were literally
formed yesterday such as those oyster shells, scallops and corals currently
living and dying now, adding to the topmost layer of newly forming deposits.
Others are millions of years old. Recent deposits are subjected to all elements
in the surrounding water, and, with the state of the rivers and oceanic margins
becoming more polluted, it may be wise to find a calcium carbonate source that
is from a high quality mine, further inland, that is much less susceptible to
environmental pollutants. A reef, for example, is made up almost exclusively of
animals that use dissolved calcium carbonate in the water to make either an
internal or external calcium carbonate structure. As time goes on, the deposit
accumulates to various levels. Some deposits are thousands of feet thick while
others are just a few. It all depends on the initial environment and time."
The majority of the
coral calcium products sold in the United States is made of calcium carbonate
from coral reefs, which, apart from age, is no different than calcium carbonate
from other sources such as limestone. Some studies have even stated the claimed
benefits of coral calcium are derived from a separate compound found in the
water, calcium aspartate, and not the coral itself.7
If all calcium
carbonate sources are basically the same in regard to source and bioavailability,
what is the best way for manufacturers to choose a source? Five criteria should
be considered: grade, lead level, quality, color and cost. For grade, there are
basically just two--food and pharmaceutical--with numerous permutations. For
lead level, California Proposition 65 has set the standard for dietary
supplement lead intake, and has had a great impact on the calcium carbonate
industry. Tablet manufacturers are requiring lower lead levels, with some
sources moving into the low parts per billion range. Basically, the lower the
lead level, the more options for formulation.
Quality of the material
has come under scrutiny lately. Besides ensuring the material meets all chemical
specifications (including lead), a manufacturer needs to pay close attention to
the microbiological activity of the material. Laboratory tests conducted by
Silliker Laboratories in Carson, Calif., for Nutri Granulations showed micro
counts as high as 31,000 APC in some coral samples. With a USP standard
specification of less than 3,000 APC, diligence in raw material testing is
critical.
Overall, selecting a
calcium carbonate raw material depends on how it meets the manufacturer's needs.
Given the similarities of the various sources, as well as similar
bioavailability levels, it is apparent that the end benefits for the consumer
are the same, regardless of the origin of the calcium.
References
1.
Harper's Review of Biochemistry, 17th ed., p. 575-6, 1979; Normal and
Therapeutic Nutrition, 14th ed., p. 105-6, 1972.
2.
Modern Nutrition in Health and Disease, p. 151, 1994.
3.
Sheikh MS et al. "Gastrointestinal absorption of calcium from milk
and calcium salts." NEJM, 317, 9:532-6, 1987.
4.
ibid.
5.
Havala S, "Calcium content in tahini." Vegetarian
Journal, July/August 1996.
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