Introduction: Oxytocin (OT), a neurohypophysial hormone regulated by estrogen and leptin, may play a role in bone metabolism in humans as suggested by animal studies. This study assessed the relationship between OT and bone status in a large population of postmenopausal women.
Subjects and methods: Subjects were included in the Osteoporosis and Ultrasound study, a 6-year prospective study in a population-based cohort. Final visit data were used for this cross-sectional study. OT, leptin, and estradiol serum levels were measured in 1097 postmenopausal women and compared with bone mineral density (BMD), fractures, and the bone turnover markers (BTMs) procollagen type 1 N-terminal propeptide, bone alkaline phosphatase, and C-telopeptide of type 1 collagen.
Results: The median age was 70.8 years, 16% were osteoporotic, 48% were osteopenic, and 29% had at least one fracture. The OT serum level was related to spine (r = +0.12, P = .0002) and total hip BMD (r = +0.21, P < .0001) and with BTM (procollagen type 1 N-terminal propeptide: r = -0.13, P < .0001, bone alkaline phosphatase: r = -0.07, P = .02, C-telopeptide of type 1 collagen: r = -0.18, P < .0001). The relationship of OT with BMD was independent of BTM. After adjustment for confounding factors, the correlation between OT serum level and BMD remains significant at the hip in women with unmeasurable estradiol or leptin above the median value. There was no significant relationship between OT serum levels and fractures.
Conclusion: High OT levels are associated with high BMD, especially at the hip in women with low estradiol or high leptin serum levels. The mechanism may be explained by the effect of OT on bone turnover.
Trial registration: ClinicalTrials.gov NCT01192893.