Calcium absorption and calcium bioavailability.

Calcium is important for bone health. It has been customary to focus on dietary calcium intake, but of central importance for the body needs in the individual patient is the actual calcium absorption. This absorption consists of an active vitamin D-mediated component and a passive diffusional component. A number of different methods are available for the evaluation of calcium absorption. At present the calcium absorption tests using calcium isotopes (radioactive or stable) appear to be the most reproducible way of determining calcium absorption. The major nutrient sources for calcium are milk and milk products, whereas some of the green vegetables have a low bioavailability of calcium. When deciding whether an increased calcium intake is advisable, the following questions must be answered. What is the calcium absorptive status of the patient? How should the calcium supplement be dispensed? What calcium salt should be used? When should calcium supplements be taken? What is the compliance of the patient? When should the treatment be evaluated? The calcium supplement might be taken as milk (or milk products) or, in patients with lactose intolerance, as calcium supplements. Quite a number of calcium supplements are available on the market, and many of them are marketed without proper knowledge of the bioavailability of the actual preparation. For the benefit of our patients it is now reasonable to demand such investigations before marketing calcium supplements.