and this is especially true in old age. It is also especially dangerous in old age, when a broken hip may spell the end of independent living and a shortened life span.
One of the complexities in determining the relationship between calcium consumption and bone health is the fact that calcium absorption rates are highly variable and are more closely tied to calcium levels than is the rate of calcium intake itself, as Heaney (2000) notes. Heaney (as well as a number of other scholars, of course), notes that one of the most important aspects in considering bone health is the fact that it is calcium absorption efficiency that is responsible for more of the variability in the calcium balance in a body than variability in the intake levels of calcium:
Moreover, the 95% probability range for the intake-adjusted absorption fraction is broad, extending from 0.12 to 0.41 in healthy adults at an intake of 20 mmol (0.8 g) Ca/d (2). This means that, after allowance is made for calcium entering the gut with digestive secretions, net absorption ranges from -0.027 to 0.245 g/d. Thus, it is understandable that there would be considerable interest in identifying factors that may influence calcium absorptive efficiency (Heaney 2000).
Heaney, who has done a repeated experiments in this field, has determined that the relationship between phosphorus and calcium is more complex than previously thought, because while phosphorus can inhibit the absorption of calcium, calcium can also inhibit the intake of phosphorus. Moreover, as has been previously established, a number of other factors also influence calcium uptake. One of these factors is the metabolic relationship with phosphorus. However, Heaney (2000) notes that the relationship between calcium and phosphorus is less important than some previous research suggested: Heaney notes that phosphorus has been "widely believed to form insoluble complexes with calcium" and as a result is considered to b...