There are multiple sources of calcium and many brands of calcium. Regardless of the multiple brands and forms of calcium, some forms of calcium are better absorbed. This raises the subject of coral calcium. Coral calcium is simply calcium carbonate derived from coral beds. What's so special about coral calcium? Well, it is said to be better absorbed by the human gut, thus giving you more of what you truly need or even more bang for your buck. You be the judge.
In a study by Ishitani and others (J Nutr Sci Vitminol. 1999; 45(5):509-17), one group of patients were fed crackers with powdered calcium carbonate from a non-coral source and the other group powdered coral calcium carbonate. There was a significant difference between the absorption of calcium between the two groups. The coral calcium group had superior absorption.
Calcium With D
Coral Calcium usually have trace minerals which may contribute to absorption. Be careful of how your coral calcium is harvested. Make sure it comes from a reputable company and is certified pure from harmful contaminants.
Animal studies have shown enhanced bone growth at injured site (periodontal) when that tissue is implanted with calcium from a coral source. J Clin Periodontol. 2005; 32(1):104-10. So, not all calcium supplements are created equally.
So don't be fooled! There are varying quality of calcium supplements based on the form of calcium and calcium content. Always read the labels and ask questions. Again, look for not only the form of calcium but the source of the calcium. For example, people who are on dialysis and use a calcium product to neutralize excess phosphorous should use calcium acetate, not carbonate. The reason for this is that calcium acetate is not as bioavailable or absorbed. That's why kidney patients use the acetate because they are usually calcium overloaded.
A final word: If you are vitamin D deficient, your body will not efficiently absorb calcium. You need adequate intake of calcium and vitamin D in addition to a healthy liver and kidneys. Ask your healthcare provider to see if you need to have your vitamin D levels assessed.