Objective: To study the age-related changes of bone formation markers, i.e., serum bone alkaline phosphatase (sBAP) and serum osteocalcin (sOC), bone resorption marker, i.e., cross-linked N-telopeptides of type 1 collagen (sNTX), and bone mineral density (BMD) in healthy men.
Methods: Serum sBAP, sOC, and sNTX of 389 randomly selected males, aged 20 - 80, all of Han nationality, were measured by using enzyme-linked immunosorbent (ELISA). Dual energy X-ray densitometer was used to measure the BMD of the lumbar vertebrae, left femoral neck, Ward's triangle, and hip. The relationships of these markers to age were analyzed.
Results: (1) The sBAP, sOC, and sNTX were negatively correlated with age, the cubic regression model being better with age-related changes of bone biochemical markers as compared with the other regression models (R(2) = 0.013 - 0.029, P < 0.05); (2) When all subjects were stratified by 10-years, the bone biochemical marker values were the highest in the age group 20 - 29, with the sBAP of 30.9 U/L +/- 12.6 U/L, sOC of 12.6 microg/L +/- 6.2 microg/L, and sNTX of 18.2 micromol/L +/- 6.6 micromol/L; then decreased with aging and to a nadir level in the age group 50 - 59, with the sBAP of 26.9 U/L +/- 8.6 U/L, sOC of 9.2 microg/L +/- 5.3 microg/L, and sNTX of 15.6 micromol/L +/- 6.1 micromol/L. After the age of 60, sNTX increased slightly 16.0 micromol/L +/- 6.1 micromol/L, however, BAP and sOC remained stable; (3) After adjustment for age, height, weight, BMI and smoking, serum BAP was negatively correlated with BMD of multiple skeletal sites. sOC was inversely associated with BMD of multiple skeletal sites except lateral spine; and sNTX was negatively correlated with BMD of the lumbar spine and total hip.
Conclusion: Negatively correlated with BMD, sBAP, sOC, and sNTX may be sensitive and relatively specific markers to evaluate age-related changes of bone turnover.