Menopause is accompanied by a decrease in bone mineral density which can be caused by a reduction in bone volume and/or degree of bone matrix mineralization. Both of them are suggested to contribute to the increased fracture risk in postmenopausal individuals. In the present work, we aimed for information whether a drop in bone matrix mineralization is occurring in the perimenopausal stage of women. For this purpose, we measured the bone mineralization density distribution (BMDD) by quantitative backscatter electron imaging (qBEI) in n=17 paired transiliac bone biopsy samples premenopausal baseline and 12 months after last menses (taken at the average ages of 49±2 and 55±2 years) from healthy perimenopausal women. Our study participants were a subgroup of a larger study where significant perimenopausal increases of about 80% in both activation frequency and bone formation rate have been reported.
In the current study, we found that none of the BMDD parameters of the postmenopausal BMDDs were significantly different compared to those of the premenopausal ones (signed rank tests, all P>0.05). Moreover, the average calcium concentration of cancellous bone was found to be in the normal reference range before as well as after menopause (22.11 (21.88; 22.75) wt%Ca vs 22.09 (21.79; 22.60) wt%Ca, median (25th, 75th percentiles) respectively, P=0.255).
Our findings surprisingly revealed that the rise in histomorphometric bone turnover indices was not accompanied by changes in bone matrix mineralization. This might indicate that the substantial increase in bone turnover took place during the last months before the second biopsy (in line with the previously reported transmenopausal increases in osteocalcin) and the bone mineralization changes were lagging these bone turnover changes. We conclude that during the perimenopausal observation time BMDD measured by qBEI is preserved and does not contribute to decreases in bone mineral density.
17 May 2014 - 20 May 2014