The influence of Na load on bone metabolism was investigated in postmenopausal women using urinary deoxypyridinoline (DPD) as a marker of bone resorption. In a cross-over study, fourteen postmenopausal women were divided into two groups of seven. A fixed diet providing 816 mg Ca/d with either 60 or 170 mmol Na/d was consumed. At the end of an 8 d period the groups switched diets for a further 8d period. Urine was collected daily for the last 4d of each period. There was no significant difference in DPD excretion between high-Na and low-Na diets (129 nmol/d v. 132 nmol/d; P = 0·18). There was, however, a significant relationship (P = 0·02) between the changes in DPD excretion and urinary Ca. Plasma Mg fell from 0·83 to 0·81mmol/l on the high Na intake (P<0·001), but there was no significant effect on plasma Ca or intact parathyroid hormone levels. It is concluded that varying dietary Na intake may affect Ca and Mg metabolism, but we were unable to demonstrate an effect on bone resorption at the levels of intake used
