Does serum osteoprotegerin level relate to fragility fracture in elderly women with low vitamin D status?

Background: Increased osteoprotegerin (OPG) with elevated bone turnover is supposed to be a homeostatic mechanism limiting bone loss.

Material/methods: Whether osteoprotegerin relates to low-energy fracture in elderly women was investigated by analyzing the relationship between OPG and bone turnover. Sixty-nine women with a first fragility hip fracture participated. The reference group consisted of 23 age-matched women. Serum calcium, 25-OHD3, parathormone, osteocalcin (OC), cross-linked C-terminal telopeptides (CTX-I), tartrate-resistant acid phosphatase (TRAP5b), and osteoprotegerin were assayed immediately post-fracture.

Results: In both groups, median vitamin D and calcium concentrations were in the low reference range, CTX-I were moderately elevated, and TRAP5b activity and parathormone were within the reference range. Significantly lower osteocalcin, a trend to higher OPG, and an inverse correlation between OPG and osteocalcin was found in the fracture group. The distribution of fracture was related to osteocalcin and OPG concentrations: the lower the OC level, the higher the number of women with fracture at increasing OPG concentrations. A relative imbalance between bone formation and resorption was found in the fracture group. The lowest osteocalcin level (Q1) was observed only and vitamin 25-OHD3 insufficiency predominantly in the fracture group and higher OPG, TRAP5b, and elevated CTX-I concentrations (Q3) were found more often or predominantly in this group.

Conclusions: The data demonstrate a relative imbalance between bone formation and resorption associated with fragility fracture in elderly women with low vitamin D status. The authors suggest that compensatory elevation of serum OPG, particularly with reduced bone formation, is insufficient to limit bone loss leading to fracture.