Annual skeletal balance and metabolic bone marker changes in healthy early postmenopausal women: results of a prospective study

The aim of this study was to establish the duration and annual rate of menopause-related bone loss and to investigate the relationship between bone turnover and bone loss in early healthy postmenopausal women. The rate of change in bone mineral density (BMD) at the lumbar spine and in bone turnover was measured twice at the exact interval of 12 months by dual-energy X-ray absorptiometry (DXA) and by the determination of plasma alkaline phosphatase levels (ALP) and fasting urinary hydroxyproline/creatinine ratio (OHPr/Cr), respectively, in 123 healthy premenopausal and postmenopausal women 45–60 years of age. The subjects were divided into nine groups according to their menstrual status and years since menopause (YSM). Annual bone loss at the lumbar spine of women who were menopausal for 1, 2, 3, 4, and 5 years was −2.62 ± 0.37 (95% confidence interval −3.66, −1.58), −3.87 ± 0.96 (−6.02, −1.73), −2.50 ± 0.37 (−3.29, −1.70), −2.86 ± 0.73 (−4.44, −1.27), and −1.54 ± 0.41 (−2.42, −0.66), respectively, and was significantly less than zero. But, the annual bone loss of women who were premenopausal or menopausal for 6, 7, and 8 years was −0.76 ± 0.60 (−2.04, +0.53), −1.16 ± 0.68 (−2.61, +0.29), 0.24 ± 0.48 (−0.78, +1.26), and 0.16 ± 0.63 (−1.18, −1.49), respectively, and was not significantly different from zero. These results demonstrate that the early hormone-dependent bone loss commences in the first year after menopause and is arrested within 6 years after the onset of menopause. The overall bone loss for this phase is estimated to be approximately 15%. Annual change in ALP and OHPr/Cr seems to indicate that bone resorption prevails on bone formation in the first 2 YSM, whereas osteoblastic activity relatively prevails from YSM 3 to YSM 5, which explains the progressive repairing of the imbalance between bone resorption and formation.