Dietary calcium, sodium, phosphorus, and protein and bone metabolism in elderly Japanese women: a pilot study using the duplicate portion sampling method.

Objectives: Associations between dietary factors and bone metabolism in Asians have not been thoroughly investigated. The purpose of this study was to determine the effect of dietary intake of calcium (Ca), phosphorus (P), sodium (Na), and protein on bone metabolism in elderly Japanese women by the duplicate portion sampling method.

Methods: The subjects were 43 healthy female volunteers (mean age, 68.3 y; standard deviation, 6.8). Dietary nutrients were directly determined by using a 24-h duplicate meal portion. Serum osteocalcin and bone alkaline phosphatase and urinary deoxypyridinoline (DPD) and type I collagen cross-linked N-telopeptides (NTX-I) were measured as markers of bone turnover. Hormones related to bone metabolism, including serum 25-hydroxyvitamin D(3), 1,25-dihydroxyvitamin D(3), and intact parathyroid hormone also were determined. Urinary parameters were corrected for urinary creatinine concentration.

Results: The mean (standard deviation) daily dietary intakes of Ca, P, Na, and protein were 660 (195) mg, 996 (208) mg, 4080 (1142) mg, and 63.9 (15.5) g, respectively. Dietary Ca was negatively correlated with urinary DPD (r = -0.417, P = 0.005) and NTX-I (r = -0.324, P = 0.034), and dietary P was negatively correlated with urinary DPD (r = -0.307, P = 0.045). Multiple regression analysis showed that only dietary Ca was associated with urinary DPD and NTX-I. Dietary Ca intake was significantly associated with bone resorption markers, but no other dietary factors were associated with any of the biochemical markers.

Conclusion: The major factor having an adverse effect on the bone health of the elderly Japanese women is low Ca intake and not other dietary minerals or protein.