Study Of The Relationships Of Serum Bone Alkaline Phosphatase (BAP),Serum Osteocalcin (sOC),Serum Cross-linked N-telopeptide Of Collagen Type Ⅰ(sNTX) With Age And Bone Mineral Density (BMD) In Males

AIM To study the relationships of serum cross-linked N-telopeptide of collagen type I (sNTX), serum bone alkaline phosphatase (BAP) with age and bone mineral density (BMD) in normal men aged 20-80 years old.METHODS sNTX and BAP were measured using ELISA, areal BMD at anteroposterior (AP) lumbar spine, supine lateral lumbar spine, and hip using DXA (QDR 4500A), in 309 normal males. Correlations of bone biomarkers with age and BMD were fitted in the whole male population by ten regression models.RESULTS (1) sBAP and sNTX were negatively correlated with age (all P < 0.05). The cubic regression model was better fitted with age-related changes of bone biomarkers as compared to other regression models, with the coefficients of determination (R~2) of fitting curve 0.029, 0.026, respectively (P < 0.005). (2) All subjects were stratified by 10-year age groups, the sBAP and sNTX values during 20-29 years of age were the highest, then decreased gradually, after 40 years lower the highest values, and to the lowest level in the 50-59 years of group. After 40 years the sNTX values increased slowely while the sBAP values keep stable. No difference was found in 40～59 years of age groups. (3) BMD values at all sites were negatively correlated with age (r = -0.151, -0.185, -0.259, -0.428, -0.570, respectively. all P < 0.05). (4) All subjects were stratified by 10-year age groups, BMD values at all sites were the highest during 20-29 years of age, then decreased gradually, and keep stable during 40-60 years of age, and decreased again post after 60 years of age. Accumulative lose rates of BMD at all sites rang in 7.29%-39.29%, that of BMD at Ward's region highest. (5) BMD values at all sites were negatively correlated with BAP; After adjusted age, weight and smoking, BMD values at all sites but supine lateral lumbar spine were negatively correlated with BAP (r=-0.171, -0.148, -0.191, -0.105, P < 0.05); BMD value at anteroposterior (AP) lumbar spine was negatively correlated with sNTX (r =-0.164, P < 0.05); No correlations were found between sOC values and BMD values at all sites. (6) All subjectes were categorized into two groups according to whether smoking or not, there was a lower mean BMD of all sites and a higher sBAP values in those smoking men (all P < 0.05). (7) After adjusted age and BMI, smoking years was negatively correlated with BMD values at at all sites but supine lateral lumbar spine. Smoking amount per day was negatively correlated with BMD values at anteroposterior (AP) lumbar spine and Ward's region (all P < 0.05). (8) Multiply regression analysis was made, taking BMD values at all sites as dependent variables, and age, BMI, sBAP, sNTX, smoking age and quantity as independent variables. Age and BMI enter all regression equation of BMD in all sites; smoking enters the regression equation of BMD at anteroposterior (AP) lumbar spine and hip region and Ward's region; besides the regression equation of supine lateral lumbar spine, BAP enters the others of BMD in all sites (all P<0.05) . sNTX enters the ones of BMD at anteroposterior (AP) lumbar spine, which suggest age, BMI, and smoking, BAP and sNTX were the decision factors of BMD. Age accounts for the percentages of variance of BMD were 17.7%, 27.4%, 27.8%, 49.9% and 56.6%, whereas BAP explains the percentages of variance of BMD 16.5%, 18.0%, 13.4 and 10.8% respectively at anteroposterior (AP) lumbar spine, supine lateral lumbar spine, total hip, femoral neck and Ward's region. NTX acconts for the percentages of variance of BMD 15.7% at anteroposterior (AP) lumbar spine.CONCLUSION (1) Age is an important factor affecting on bone turn over in males; sBAP and sNTX may be the sensitive and relatively specific markers to evaluate age-dependent decreasing of bone turnover. (2) Bone lose with age in men due to bone turn over level decreasing and a focal imbalance between resorption and formation. (3) BMD values at all sites are negatively correlated with BAP; After adjusted age, weight and smoking, BMD values at all sites but supine lateral lumbar spine are negatively correlated with BAP. BMD value at anteroposterior (AP) lumbar spine is negatively correlated with sNTX. (4) Smoking raises bone turnover rate and accelerates bone lose.