From Metabolically Healthy Obesity to Metabolically Unhealthy Obesity Populations: Decreased Bone Turnover Bioactivity

PURPOSE: A bone turnover marker reflects bone bioactivity. The effects of metabolically healthy compared with metabolically unhealthy obesity phenotypes on bone metabolism are not well understood. The aim of the study was to evaluate differences of bone transformation indexes in these two obesity phenotypes. PATIENTS AND METHODS: A total of 419 obese subjects were recruited, 64 with metabolically healthy obesity (MHO) and 351 with metabolically unhealthy obesity (MuHO). BTMs and clinical parameters were measured. RESULTS: Bone metabolism indexes, including tartrate resistant acid phosphatase (TRACP, p < 0.05), β carboxyl terminal peptide of collagen (β-CTX, p < 0.01), and bone alkaline phosphatase (BAP, p < 0.01), were higher in subjects with MHO than MuHO, but parathyroid hormone (PTH) was lower (p < 0.05). The between-group difference in serum calcium was not significant. Low bone turnover activity was associated with significant hyperglycemia, insulin resistance, and body fat index (p < 0.05). Multivariate logistic regression found that TRACP, β-CTX, and BAP were independently associated with the presence of MHO. Receiver operating characteristic curve analysis found that the maximum area under the curve value for the definition of MHO was (0.8221) and was obtained when sex, age, body mass index (BMI), TRACP, β-CTX and BAP were included simultaneously, resulting in a sensitivity of 81.25% and specificity: 72.3%. CONCLUSION: The MHO group had significantly increased circulating TRACP and β-CTX compared with the MuHO group and BAP levels were within the physiological range. Obesity with the metabolically healthy phenotype had slightly increased bone turnover activity that may be an early compensatory response of skeletal metabolism to the increased BMI.