As one of the leading proponents of natural products, I am a firm believer in the value of proper nutritional supplementation. Over the years, however, I have been angered by the shameless marketing of bogus products with unsubstantiated, absolutely ridiculous claims. The latest in this growing list of shame is “coral calcium.” Since I am fielding an ever-growing number of questions about this product, I have decided to finally address it formally. Be patient, read the whole article and you will hopefully see that while it is true that calcium is an essential mineral, coral calcium is not a quality calcium supplement.

What is Coral?

Coral is composed of tiny, fragile living organisms called coral polyps. The coral polyps take calcium carbonate or limestone from the sea and build protective structures around themselves. As coral polyps die, new generations of coral polyps then grow on top of the coral, and coral reefs are formed.

While coral reefs cover less than 1 percent of the planet’s surface, they are homes to over 25 percent of all marine life (over 4,000 different species of fish, 700 species of coral and thousands of other plants and animals). Since coral reefs are among the world’s most fragile and endangered ecosystems, strict laws are enforced to preserve them.

What is Coral Calcium?

Since it is severely illegal to mine “live” coral reefs, coral calcium has to come from a different source. Marketers tell us that it is either taken from old seabeds buried in the so-called “pristine” desert, mined from “fossilized coral sands that accumulated on the sea floor” or harvested from “only coral that washes up on the shore.” Sounds good, right? The bottom line, however, is that it doesn’t make much difference.

What is the Hype?

What the marketers of coral calcium do is exploit and exaggerate the known importance and function of calcium and then try to tie those benefits and more to their product. Here is just a brief list of the diseases claimed to be miraculously cured by coral calcium:

  • Cancer
  • Diabetes
  • Arthritis
  • Heart disease
  • Osteoporosis
  • Eczema
  • Alzheimer’s disease
  • Fibromyalgia
  • High cholesterol
  • Muscle cramps
  • Kidney stones
  • Gallstones
  • Gout
  • Indigestion
  • Chronic fatigue syndrome
  • Lupus
  • Hiatal hernia
  • Hypertension
  • Headaches

Wow!! Wouldn’t it be fantastic if it were true that coral calcium could cure all of these diseases? While it is true that in most of these diseases you can find a small, indirect association between calcium and the disease, the marketers take it way over the top.

Is Coral Calcium a Superior Form of Calcium?

Sorry, it is not. The calcium content of coral calcium ranges from 24 to 38 percent and is composed primarily of calcium carbonate. The marketers often call it “aragonite” or “calcite” to confuse and mislead the masses into thinking it is something different than the chief ingredient of Tums. Marketers use the “coral story” to hype their product, but just like mined land sources of calcium (e.g., limestone and dolomite), the bottom line here is that the calcium is bound in the form of an inorganic salt.

There are considerable dangers in using these mined sources of calcium, whether it comes above sea level or below, or whether the source is fossilized coral, limestone, or dolomite. For millions of years, volcanoes have been spewing their molten lava and ash full of poisonous heavy metals like lead, mercury, cadmium and iridium into the earth and sea. Although I have not seen a detailed analysis of heavy metals for a coral calcium product, even the marketers acknowledge the high content of aluminum by stating that their product contains montmorillonite. Some will tell us that montmorillonite is a natural clay that comes from volcanic ash. Others will come clean and recognize it as colloidal aluminum silicate.

I should point out that there has been one study comparing the absorption of coral calcium to calcium carbonate. However, this study is fraught with methodological errors and used urinary calcium measurements instead of more accurate measurements of calcium absorption—after all, it is not how much calcium you excrete that is important; it is how much you absorb and retain. No conclusions can be made from this study as it looks like it was constructed simply to promote coral calcium instead of answering more important questions.

Why Should I Avoid Natural Sources of Calcium?

Again, the major problem is lead contamination. This issue has been addressed in numerous studies looking at commercial calcium supplements. In one study, the lead content of 136 brands of calcium supplements was determined. The calcium in the products was derived from natural sources (bone meal, dolomite or oyster shells) or was synthesized and/or refined (chelated and nonchelated calcium such as calcium citrate and carbonate). Two-thirds of those calcium supplements failed to meet the acceptable lead levels (1.5 mcg per daily dose of calcium) in consumer products. The most likely products to contain lead were the natural forms, while the products most likely not to contain lead were products like calcium citrate or refined (purified) calcium carbonate. The results from this study are consistent with all of the others. It is quite alarming, as lead from calcium supplements definitely contributes to elevated lead levels in the body.

So What is the Best Form of Calcium?

The bottom line is that the most widely used form—calcium carbonate—appears suitable for most people. The possible exception is in people who do not produce enough stomach acid, especially postmenopausal women. But even in these people, it appears that taking calcium carbonate with food overcomes this shortcoming.

While calcium bound to citrate and other Krebs cycle intermediates such as fumarate, malate, succinate and aspartate, as well as lactate, have advantages over calcium carbonate in that they are (a) easily ionized, (b) almost completely degraded and utilized by the body, (c) virtually nontoxic and (d) able to increase the absorption of not only calcium but other minerals as well, the problem with these calcium supplements is their bulk. It basically requires three to four times as many capsules or tablets to provide the same level of calcium compared to calcium carbonate sources.

It is also important to point out that microcrystalline calcium hydroxyapatite—another hyped form of calcium—does not provide any greater benefit than other forms of calcium, including calcium carbonate. In fact, in one study looking at five commercially available forms of calcium, microcrystalline calcium hydroxyapatite was the poorest absorbed.

Advantages and Disadvantages of the Various Forms of Calcium

Form Disadvantages Advantages
Calcium carbonate May not be adequately absorbed in people with insufficient output of stomach acid. Should be taken with foods for maximal absorption. Inexpensive. Easier to take because it is not as bulky as other forms.
Coral calcium, oyster shell calcium, dolomite and bone meal May contain high levels of lead and other impurities. Since these sources of calcium are essentially calcium carbonate, it makes more sense to used purified calcium carbonate products. None.
Calcium citrate, calcium bound to other Krebs cycle intermediates, calcium gluconate, calcium lactate Larger molecule is bulkier than calcium carbonate, thus requiring more tablets/capsules to achieve the same dosage as calcium carbonate. Easily absorbed regardless of the output of stomach acid.
Calcium phosphate Poorly absorbed compared to other forms. Has a greater effect in blocking the absorption of iron and other minerals. Least likely to cause constipation.
Microcrystalline calcium hydroxyapatite Poorly absorbed compared to other forms. More expensive. May exert additional benefits in bone health due to other components.


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