Almost all the calcium that makes its way into dietary supplements is mined from the earth and occurs as calcium carbonate. Another source for the same type of calcium is coral reefs. A spate of advertisements have claimed that this form of calcium is superior and more absorbable. If we don a scuba tank and do some investigating, however, we find just a few studies that support such bubbly claims. In one human study, 12 subjects ate one serving of crackers fortified with either 525 mg of calcium from Japanese coral (containing a 2:1 ratio of calcium to magnesium) or from terrestrial calcium carbonate. Researchers found a modestly stronger absorption with coral calcium, though the method of measurement was less than exact. In another study, researchers found that oral supplementation with a different kind of Japanese coral calcium, containing a 17:1 ratio of calcium to magnesium, boosts the immune system of mice more than oral supplementation with terrestrial calcium carbonate.

No human studies have yet examined the effects of coral calcium on bone density or bone metabolism—the real reasons behind supplementation with calcium from any source. Because numerous studies on humans support taking land-derived calcium carbonate, or other forms such as citrate or citrate malate, to improve or maintain bone density, the touted benefits of coral calcium still sound fishy. And consider, too, that widespread use of these products might damage fragile coral reef environments.

Nutrition and exercise biochemist Anthony Almada, MS, has collaborated on more than 45 university-based studies, is co-founder of Experimental and Applied Sciences (EAS), and is founder and chief scientific officer of IMAGINutrition.