Calcium, absorption balance, osteoporosis

In extensive studies of the effect of fluoride In patients with osteoporosis carried out In this Research Unit, a therapeutic dally dose of 45 mg fluoride per day was used as sodium fluoride. The main effect of fluoride on calcium metabolism was a decrease of the urinary calcium, while the fecal calcium did not change and the calcium balance also remained unchanged. Also, the Intestinal absorption of calcium remained unchanged during the high fluoride Intake (Table I), The decrease In urinary calcium, Induced by sodium fluoride, may be due to decreased bone resorption, a very desirable effect for patients with osteoporosis. 

Phosphate balance in adults is almost always zero, in contrast to calcium balance, which is usually negative, because of the effective action of PTH on renal tubules to block Pi reabsorption. In late life, however, intestinal phosphate absorption decreases and the serum phosphate concentration declines. These physiological decrements may contribute to disease, especially to increased bone loss and osteopenia or more severe osteoporosis. Typically, these changes in Pi balance are also accompanied by similar changes in calcium balance. Too little dietary phosphorus and too little dietary calcium may be determinants of low bone mass and density and, hence, increased bone fragility. The usual scenario invoked to explain osteoporosis in old age, however, is that too little dietary calcium in the presence of adequate dietary phosphorus stimulates PTH release and bone loss (Figure 1). 

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