The effect of dietary sodium on calcium metabolism in premenopausal and postmenopausal women

Objective: To investigate the effects of high and low sodium diets on urinary calcium, bone turnover and calcium absorption in pre and postmenopausal women. Design: Experimental, prospective and longitudinal study. Setting: Samples were taken at the hospital and the diets were followed at home. Subjects: Volunteers were recruited from the hospital and were either hospital staff or post-graduate students. No volunteers failed to complete the study but one was omitted from analysis due to lack of compliance. Interventions: Eleven healthy premenopausal women aged 22–47 y and 11 healthy postmenopausal women ages 45–70 y followed a high (300 mmol/d) and a low (50 mmol/d) sodium diet for one week each. On the 7th day of each diet, blood and urine samples were taken. Results: On the high sodium diet 24 h urinary sodium and calcium values relative to creatinine were significantly higher for all subjects (P<0.05). Postmenopausal women on the high sodium diet had biochemical evidence of increased bone resorption in relation to the low sodium diet. However in premenopausal women there was no such change. Calcium absorption did not change significantly in either group. Conclusions: It appears that postmenopausal, but not premenopausal, women respond to a high sodium diet by an increase in bone resorption which may lead to reduced bone density. Sponsorship: Arthritis and Rheumatism Council Project Grant R44.