J Bone Miner Metab (2003) 21:415–420 DOI 10.1007/s00774-003-0437-3 © Springer-Verlag 2003 The relationship of sodium intake to calcium and sodium excretion and bone mineral density of the hip in postmenopausal African-American and Caucasian women Laura D. Carbone 1 , Andrew J. Bush 2 , Karen D. Barrow 1 , and Andrew H. Kang 1 1 Department of Medicine, University of Tennessee Health Science Center, 956 Court Ave, Coleman Bldg., Room E336, Memphis, TN 38163, USA 2 Department of Preventive Medicine, University of Tennessee Health Science Center, Memphis, TN, USA Introduction Sodium intake in the United States exceeds recom- mended allowances in both African-Americans and Caucasians [1]. The role of sodium in hypertension is well documented; however, less well appreciated is the fact that sodium may also affect bone health. Calcium and sodium share a common transport mechanism in the kidney. Reabsorption of calcium parallels the reab- sorption of sodium at the renal tubular level. Sodium may directly (through effects on tubular reabsorption) and indirectly (through effects on parathyroid hormone (PTH)) inﬂuence renal reabsorption of calcium and re- sult in increased calcium excretion [2,3]. In Caucasian postmenopausal women, it has been estimated that ap- proximately 1 mmol calcium is excreted per 100 mmole sodium [4]. Epidemiological studies in patients with idiopathic hypercalciuria suggest that hypercalciuria is linked to low bone density [5–7], and low bone density is a signiﬁcant determinant of osteoporotic fractures [8]. However, the relationship of sodium intake to bone mineral density (BMD) is somewhat controversial, with some authors suggesting that 24-h urine sodium levels and BMD are negatively correlated [9], and others sug- gesting that there may actually be a small beneﬁcial effect of sodium on bone [10]. The purpose of this study was to determine the rela- tionship of sodium excretion to calcium excretion, the factors that may modify the relationship of sodium excretion to calcium excretion, and the relationship of calcium and sodium excretion to BMD of the total hip in elderly African-American and Caucasian postmeno- pausal women. Abstract During the past several decades in the United States, there has been a shift in dietary habits, with an in- creased consumption of processed foods that are high in so- dium. It is known that calcium and sodium metabolism are linked and that higher sodium intakes may increase calcium excretion. Epidemiological studies in patients with idiopathic hypercalciuria suggest that hypercalciuria is linked to low bone mass. However, the relationship of sodium intake to bone mineral density (BMD) is controversial in Caucasians and has not been explored in African-Americans. To deter- mine the consequences of sodium intake on bone in African- American and Caucasian postmenopausal women, sodium and calcium excretion and BMD of the total hip were mea- sured in 50 Caucasian and 39 African-American postmeno- pausal women. After adjustment for race and urine volume, sodium excretion was a signiﬁcant predictor of calcium excre- tion (P  0.01). This relationship was modulated by calcium intake (P  0.01), but not by race (P = 0.63). There was no signiﬁcant effect of sodium excretion (P = 0.42) or calcium excretion (P = 0.90) on BMD of the total hip after adjusting for race and urine volume. Sodium excretion is a signiﬁcant predictor of calcium excretion in both postmenopausal African-American and Caucasian women. The relationship between sodium and calcium excretion is modulated by cal- cium intake, and the relationship is strongest at low calcium intakes (1000 mg/day). However, sodium excretion in the range of 53.75–283.33 mmole/g/total volume (mmole/g/TV) is not a signiﬁcant predictor of total hip BMD in elderly African- American and Caucasian postmenopausal women. Key words calcium · sodium · BMD Offprint requests to: L. Carbone Received: November 18, 2002 / Accepted: March 24, 2003