Postmenopausal osteoporosis is characterised by increased bone turnover and an imbalance between bone resorption and formation.

Bisphosphonate treatment reduces bone turnover but their effect on bone balance is yet to be fully investigated.

Using the T-score approach our aims were to:​ i) investigate the effects of oral nitrogen-containing bisphosphonates on bone balance and turnover in postmenopausal women with osteoporosis and ii) determine the relationship of the change in bone balance and turnover with the change in BMD at the lumbar spine and total hip.

Women were recruited, mean age 67 years, and randomised to receive:​ ibandronate (n = 55, 150 mg/month), alendronate (n = 54, 70 mg/week) or risedronate (n = 56, 35 mg/week). They also received calcium and vitamin D daily. A fasting serum sample was collected at baseline and weeks 1, 2, 4, 12, 13, 48 and 96. The control group were 226 healthy premenopausal women receiving no treatments. PINP and CTX were measured using the iSYSIDS analyser and BMD (in g/cm2) of the lumbar spine and total hip were measured by DXA (Hologic Inc). PINP and CTX values were log10-transformed and normalised. T-scores were calculated using the mean and standard deviation from the premenopausal group. Bone turnover and bone balance were calculated from the T-scores.

Mean levels (95% CI) of balance and turnover are shown in the table. The change in turnover at weeks 4, 12 and 48 was inversely correlated with the change in lumbar spine and total hip BMD at weeks 48 and 96, (p < .01 to p < .001). The change in balance at week 4 positively correlated with the change in total hip BMD at weeks 48, (p < .01).

Bisphosphonates resulted in an initial positive balance and a reduction in turnover. Some of these changes were associated with increases in BMD. Bone turnover is a better predictor of BMD than bone balance.