Relationship between Bone Specific Alkaline Phosphatase, Osteocalcin and Age in Osteoporotic Women

Background: Osteoporosis is a serious disabiliting disease and a leading cause of fractures, especially in postmenopausal women. Several serum markers of bone metabolism have been investigated, but their pattern over age and gender in the general population is unclear. The objective of this study was to examine the relationship between bone formation markers osteocalcin (OC), bone specific alkaline phosphatase (bALP) and age in postmenopausal women with osteoporosis. Patients and Methods: The study population was obtained from a cohort of 236 postmenopausal women who underwent osteodensitometry using dual energy X-ray absorptiometry with measurement of bone mineral density (BMD). Forty-eight (20.3%) patients (median age 62, range 49-76 years) with osteoporosis (Tscore < -2.5 SD) were enrolled in the study. There were 17 (35%) patients aged 49-59 years (Group A), and 31 (65%) patients aged over 59 years (Group B). Results: PTH (76.0±13.1 vs. 81.9±13.9 ng/L), calcium (2.23±0.41 vs. 2.32±0.56 mmol/L), and creatinine (68.1±15.2 vs. 71.0±26.1 μmol/L) serum levels did not differ significantly (p=NS) between Groups (A vs. B). In Group B patients, both OC (28.5±17.8 vs. 46.2±19.3 ng/mL; p=0.003), and bALP (57.3±12.4 vs. 66.4±8.7 U/ L; p=0.005) were higher, while the serum concentration of estradiol (78.1±18.6 vs. 66.7±17.8 pmol/L; p=0.001) was lower. Moreover, a significant relationship between age and both OC (r=0.39, p=0.008) and bALP (r=0.31, p=0.009) was found only in Group B patients, but there was no relationship (p=NS) with BMD. Conclusion: In postmenopausal women the increase of bone formation markers later in life may be an expression of increased bone turnover, which is partially the cause of osteoporosis, while the role of estrogen is still unclear.