The increase in bone mineral density by bisphosphonate with active vitamin D analog is associated with the serum calcium level within the reference interval in postmenopausal osteoporosis

<p><b>Objectives:</b> To examine the factors associated with increase in lumbar spine bone mineral density (LS-BMD) by bisphosphonates (BPs) with active vitamin D analog (aVD).</p> <p><b>Methods:</b> Two independent postmenopausal osteoporotic patients treated by BPs with aVD for 24 months (Study 1: <i>n</i> = 93, Study 2: <i>n</i> = 99) were retrospectively analyzed.</p> <p><b>Results:</b> In Study 1, LS-BMD of the patients significantly increased for 24 m (5.4%, <i>p</i> < .001). A multiple regression analysis among baseline characteristics revealed that serum calcium (sCa: 8.5–10.5 mg/dL) was associated with an increased LS-BMD by treatment (<i>r</i>²: 0.088, <i>p</i> = .02). While average sCa of the patients was 9.2 mg/dL before treatment, it increased time-dependently to 9.6 mg/dL for 24 m by treatment. As each patient had their LS-BMD five times during the study, there were four instances of %LS-BMD in each patient, resulting in 372 instances of %LS-BMD in Study 1. The smallest Akaike’s information criterion value for the most appropriate cut-off levels of sCa for %LS-BMD by treatment every 6 m was 9.3 mg/dL. The %LS-BMD by treatment for 6 m during 24 m period in patients with sCa ≥9.3 mg/dL (1.5%) was significantly higher than that in patients with sCa <9.3 mg/dL (0.8%, <i>p</i> = .038). The results of Study 2 were similar to those of Study 1, confirming the phenomena observed.</p> <p><b>Conclusion:</b> sCa was associated with an increased LS-BMD by BPs with aVD.</p