Low calcium intake is associated with increased bone resorption in postmenopausal Japanese women: Yokogoshi Study.

OBJECTIVE: Low Ca intake is common among Japanese women, but its effect on bone metabolism has not been fully elucidated. The aim of the present study was to determine the relationship between Ca intake and serum markers of bone turnover in postmenopausal Japanese women.

DESIGN: A cross-sectional study.

SETTING: A community setting.

SUBJECTS: Subjects were 595 home-dwelling postmenopausal Japanese women. Ca intake was assessed by a validated FFQ. Serum type I collagen cross-linked N-telopeptides (NTX) and osteocalcin were measured as markers of bone turnover. The relationships between demographic characteristics, lifestyles, serum Ca, vitamin D and intact serum parathyroid hormone and bone turnover were also assessed.

RESULTS: The average age of the subjects was 64.5 (sd 5.8) years and the mean Ca intake was 527 (sd 160) mg/d. Ca intake was significantly associated with serum NTX (P = 0.0104), but not with serum osteocalcin. Mean serum NTX concentration in the lowest quartile of Ca intake (<417 mg/d) was significantly higher than in the fourth, referent quartile. Among these Japanese postmenopausal women, very low Ca intake (less than approximately 400 mg/d) was associated with increased bone resorption but not bone formation.

CONCLUSIONS: Increased bone resorption may be one mechanism by which this Ca-depleted population normalizes bone metabolism and prevents osteoporosis.