Recently, there has been a tremendous amount of publicity surrounding a particular calcium supplement called "coral calcium". Coral calcium is derived from the natural coral reefs of Okinawa, Japan (1,2). Depending on the particular brand, coral calcium can be sourced from the fossilized coral located above sea level, dead coral, or the live reef itself (1,2). This specific calcium supplement is being advertised as having various health benefits, including added longevity. It is also described as having significant levels of minerals and as being a highly ionized and readily absorbable form (1,2). The purpose of this article is to help clarify the actual chemistry behind coral calcium and to reveal how it compares to other calcium supplements.

Coral calcium is composed of calcium carbonate and its absorption is based on the known properties of any calcium carbonate supplement (1-3). Calcium carbonate contains 40% calcium by weight as opposed to calcium citrate, which contains 21% calcium (4). However, the key difference between these two forms of calcium is their bioavailability. Calcium carbonate requires a substantial amount of acid to pry off the carbonate chelate and allow the calcium to be absorbed. Calcium citrate, on the other hand, is already acidic and therefore does not require a low pH in order to render the calcium available for absorption (4). Thus, while calcium carbonate supplements contain more calcium by weight, the majority of it is unavailable for tissue uptake (5). This can be a particularly important point when searching for the right calcium supplement, especially for those with low gastric acid levels common with aging (5). Even those with healthy stomach acid levels typically only absorb 22% of the calcium in calcium carbonate, whereas people with insufficient gastric acid output may only absorb 4% (5). In contrast, 45% of the calcium is absorbed from calcium citrate in people with low stomach acid (5).

Depending on the brand or supplier, coral calcium can contain anywhere from 20% to 40% calcium by weight, as well as roughly 0.5% to 20% magnesium (1,2). Many coral calcium supplements will have a 2:1 calcium to magnesium ratio, however, this is not always the naturally occurring ratio and largely depends on the source of the coral reef (1,2). In one study published in the Journal of Nutrition Science and Vitaminology, coral calcium absorption was better than absorption of a calcium carbonate supplement (6). This result may, however, be mainly due to coral calcium's magnesium level. The coral calcium used in this experiment did in fact contain a ratio of calcium to magnesium of 2:1 and the calcium carbonate used contained 1/6 the magnesium that the coral calcium had (6). While magnesium may play a role in enhancing calcium regulation and uptake (4,5), it is important to keep in mind that the best solution is to start with a highly bioavailable form of calcium in the first place.

In summary, Okinawans lead active lifestyles, eat fish and vegetable based diets, and are exposed to less toxins and stress as compared to other populations. These factors are most likely the major contributors to Okinawan longevity, not the consumption of coral calcium. Coral calcium is a source of calcium carbonate and magnesium. Multiple studies have demonstrated an enhanced bioavailability of calcium citrate compared to calcium carbonate (4,5). Chelating with Krebs cycle intermediates, such as citrate, aspartate, and malate allows calcium to be easily absorbed and enhances the absorption of other minerals (5). Pure Encapsulations offers Calcium (citrate) and Calcium Magnesium (citrate), Calcium (citrate/malate) and Calcium/Magnesium (citrate/malate), and Calcium (aspartate) and Calcium/Magnesium (aspartate). All Pure Encapsulations calcium supplements are tested for heavy metals.