The dietary intake and the urinary and fecal excretion of naturally occurring226 Ra and226 Ra balances were determined in man under strictly controlled dietary conditions. These provided the basis for calculating the226 Ra balances. These balance studies were carried out during a low calcium intake, during the addition of different amounts of calcium given as calcium gluconate, and during the intake of milk.226 Ra balances were also determined during conditions which affect the metabolism of calcium: during intravenous infusions of stable strontium, during infusions of ACTH, and during total calorie starvation. During a low calcium intake of an average of 243 mg/day, the urinary226 Ra excretion averaged 0.016 pCi/day, during a calcium intake of 1300 mg or 2600 mg/day, given as calcium gluconate, the urinary226 Ra excretion did not increase, while during supplementation of the diet with milk the urinary226 Ra excretion increased. On all calcium intakes the urinary226 Ra excretion averaged 3% of the total excretion except that it was 12% on milk intake. The major pathway of226 Ra excretion was via the intestine and the226 Ra balances were in equilibrium under all study conditions. There was no correlation between the urinary226 Ra and the urinary calcium excretion.

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