ADELAIDE, AUSTRALIA. It is generally accepted that a negative calcium balance leads to osteoporosis and bone fractures. It is also known that bone fractures are relatively uncommon in developing countries where calcium intakes are low and relatively common in developed countries where calcium intakes are high and many people supplement with calcium in order to ensure an adequate intake. Does this make sense? Dr. Christopher Nordin at the Institute of Medical and Veterinary Science believes it does. Dr. Nordin points out that it is not the total calcium intake which determines bone strength (density), but rather the difference between what is taken in and what is excreted. Research has shown that for each gram of animal protein consumed one milligram of calcium is lost in the urine. This means that a 40-gram reduction in animal protein intake reduces the urinary calcium loss by 40 mg which in turn corresponds to a reduction in calcium requirements of 200 mg (assuming an absorption of 20 per cent). A reduction in sodium (salt) intake of 2.3 grams also reduces urinary calcium loss by 40 mg lowering requirements by another 200 mg. So a person with a low intake of protein and salt might have half the calcium requirements of a person eating a typical North American diet. This and the fact that developing countries generally get more sunshine (vitamin D) than developed countries go a long way towards explaining the difference in the incidence of osteoporosis and bone fractures between different cultures and individuals. Dr. Nordin concludes that there is no single, universal calcium requirement, only a requirement linked to the intake of other nutrients especially animal protein and sodium.
Nordin, B.E. Christopher. Calcium requirement is a sliding scale. American Journal of Clinical Nutrition, Vol. 71, June 2000, pp. 1381-83