Associations between bone turnover markers and bone mineral density in older adults

Objective: To examine the associations between bone turnover markers (BTMs) and bone mineral density (BMD) in older adults aged 60-85 years. Methods: A total of 1124 men (mean age, 69.1 years) and 1203 women (mean age, 70.7 years) from the National Health and Nutrition Examination Survey 1999-2002 were included in this cross-sectional analysis. Independent variables were serum bone-specific alkaline phosphatase (sBAP) and urinary N-telopeptide (uNTx), which are biomarkers of bone formation and resorption, respectively. Outcome variable was lumbar BMD. The associations of sBAP and uNTx levels with lumbar BMD was examined using multivariable linear regression models. Results: sBAP was negatively associated with lumbar BMD in each multivariable linear regression model, and this negative association was stable in both men and women men (men: beta = -0.0028, 95% CI: -0.0046 to -0.0010; women: beta = -0.0039, 95% CI: -0.0054 to -0.0023). On the other hand, uNTx was negatively associated with lumbar BMD after adjustment of relevant covariables (beta = -0.0328, 95% CI: -0.0523 to -0.0133). However, in the subgroup analysis stratified by gender, this negative association remained only in older women (beta = -0.0491, 95% CI: -0.0751 to -0.0231). Conclusion: Our study suggested that elevated sBAP and uNTX levels correlated with decreased lumbar BMD, especially in older women. This finding indicated that maintaining BTMs at low levels may be beneficial to bone health for older adults.