Of all the minerals in the body, there is more calcium than any other. It makes up somewhere around 2% of our total adult body weight, stored mostly in our bones and teeth. Bone is made up of a crystalline mineral compound embedded within a living protein matrix. This crystalline mineral compound, called hydroxyapatite, is formed principally from calcium and phosphorus. It is essential for healthy bone development and bone maintenance, and gives our bones both strength and rigidity.
Here in the United States, about 80% of our calcium comes from dairy sources. But research indicates that dietary calcium from sources such as vegetables, fruits, or the small bones of fish such as canned salmon or anchovies, may be much more readily absorbed than calcium from dairy foods. While most Americans think they need to drink milk to get enough calcium, bok choy, a variety of Chinese cabbage, is one of the best calcium bargains around as far as absorbability per unit of energy — providing around 1800 mg calcium per 100 calories! Another good source is bones themselves: since the invention of fire, people have been boiling up bones for the rich nutrients they contain. (Homemade broth is not only curative for the common cold, it’s prophylactic for bone health!)
As for calcium supplements, it’s true that not all are created equally. We hear a lot about the different forms of supplemental calcium and which ones are best. But the biggest story with calcium is not so much about which form to use as it is about calcium absorption — which itself is contingent on a complex interplay of hormones and other factors, chief of which is related to vitamin D.
While it’s interesting that calcium comes in all these various forms, without adequate vitamin D on board (vitamin D sufficiency is commonly defined as a 25(OH)D blood level of at least 32–34 ng/mL), all the calcium in the world will result in little material gain for our bones. In fact, noted calcium researcher Dr. Robert Heaney has found that different individuals can have a nearly threefold difference in their calcium absorption rates — a phenomenon for which we currently have only limited explanation. Aside from how replete our vitamin D stores are, how well we absorb calcium has much to do with the health of our digestive system.
As to which forms optimize both absorption and bioavailability, alkalizing calcium salts are the best calcium compounds known to date. These forms include calcium citrate, calcium citrate–malate, calcium ascorbate, and calcium carbonate. Calcium citrate and its relative, calcium citrate–malate (CCM), are sources that do not require hydrochloric acid (HCl) from the stomach for absorption, so the calcium in them is very bioavailable to the body and a good choice for people with low stomach acid. Calcium in the form of calcium citrate also appears to play a protective role against the formation of kidney stones, and does not appear to interfere with iron absorption from food. Calcium carbonate is often found not to be as well absorbed as citrate, but does alkalize well in the body if taken with food. (Calcium absorption from all forms is generally better when taken with a meal.)
Regardless of what form your calcium supplementation takes, it should always be balanced with magnesium supplementation. Some bone specialists favor magnesium-centered formulations with equal or slightly more magnesium than calcium. As a rule of thumb, I recommend at least half as much magnesium as calcium (a ratio of 1 part magnesium to 2 parts calcium), and in most cases I prefer nearly as much magnesium as calcium. People with osteoarthritis, in particular, want to use equal amounts of magnesium and calcium.
Many US experts now suggest that the ideal daily calcium intake from all sources, including food and supplements, would be in the range of 1000–1200 mg. (For more on how bone serves as a calcium reserve for everyday body processes, see our article on the natural approach to bone health.) See also our list of calcium-rich foods for the best dietary sources of this important bone-building mineral.