| Background. To date, the evidence used to determine calcium (Ca) requirement was accumulated primarily in Caucasians. Limited data are available in Asian populations.; Objective. This study aims to assess Ca intake that achieves zero Ca balance, evaluate the cross-sectional association between habitual Ca intake and bone mass and the longitudinal association with bone loss in postmenopausal Chinese women aged 48--63 years, and postmenopausal within 12 years.; Methods. This thesis includes: (1) a Ca balance study, (2) a cross-sectional study on habitual Ca intake and bone mass, and (3) an 18-month cohort study on habitual Ca intake and bone loss.; 21 eligible women participated in this three-phase balance study. Each phase consisted of a 5-week treatment period with either: 0, 500 or 1000 mg/d of Ca supplementation, and followed by a 2-week washout period. During the 5th week of intervention period, 5-day balance tests were conducted using a dual stable isotope technique.; 685 community-based eligible women were enrolled for the cross-sectional study. 454 of them were further followed up over 18 months with measurements conducted at 9th and 18th month. The measurements included bone mineral density (BMD) and bone mineral content (BMC), dietary intake, physical activities, and characteristics of the subjects.; Results. (1) In the balance study, the association between Ca retention and intake was fitted with the following logistic mixed-effects model: Caretention = [454 + u1]/[1+ e (2.45 - 0.00455 x Ca intake) - 323. Based on this model, it was further predicted that a mean Ca intake of 735 (95%CI 620--951) or 628 (95%CI 530--766) mg/d was required to achieve zero balance assuming dermal Ca is 50 or 0 mg/d, respectively. (2) Multiple linear regression analyses showed that habitual dietary Ca intake had a significantly positive association with current BMD/BMC at the sites with higher load of weight bearing (the legs and hip, p < 0.05), in women with longer YSM, lower body weight or higher protein intake. Analysis of covariance (ANCOVA) showed similar results. (3) Both ANCOVA and Multiple linear regression analyses showed that habitual dietary calcium intake had a marginal beneficial effect on bone loss over the followup period at the whole body and some regions of the hip.; Conclusion. Our findings suggest that Chinese postmenopausal women require a mean intake of 735 mg Ca/d to yield zero balance. Habitual Ca intake had an independent favorable association with bone mass/bone loss, and the association with bone mass varied with YSM, body weight and protein intake. |
