| Background: This newly identified feedback loop between bone and energy metabolism is mediated by osteocalcin, an osteoblast-produced protein, and has advanced academic progress in osteology and endocrinology. Osteocalcin has been recognized as a bone-derived hormone to regulate energy metabolism recently. Based on this assumption, the present study is to examine the association between serum osteocalcin and metabolic syndrome (MetS) in a Chinese male population.Study Design and Methods: We conducted a comprehensive demographic and health survey on 4303 continuous men aged 17 to 88 years, who participated in the large-scale physical examination in Fangchenggang First People's Hospital Medical Centre from September 2009 to December 2009. The current cross-sectional study was part of the cohort, and included a total of 2344 unrelated participants. A face-to-face interview was conducted by trained physicians to get the basic information of each participant. Anthropometric measurements were performed by trained personnel using a standardized protocol. Overnight fasting venous blood specimens were drawn. Triglycerides (TG), high-density lipoprotein cholesterol (HDL-c) and serum glucose were measured enzymatically on an automatic analyzer (Dade Behring, USA). Serum osteocalcin was measured with electrochemiluminescence immunoassay on COBAS 6000 system E601 (Elecsys module)immunoassay analyzers (Roche Diagnostics, IN, Germany) with the same batch of reagents. For continuous variables, the t test was used. And for categorical variables, the X~2 test was used. Spearman partial correlation coefficients of osteocalcin, body mass index (BMI), and elements of MetS were calculated after adjusting for age. A one-way analysis of variance (ANOVA) test was used to compare the difference among multiple sets of samples. If there were differences, post hoc comparisons were followed. Then a multinomial logistic regression was performed with the number of MetS components as the outcome variable and osteocalcin as the predictor. The binary logistic regression model was used to estimate the odd ratios (ORs) for the components of MetS or MetS itself. Data management and statistical analyses were performed with the SPSS 13.0. Statistical tests were 2-sided, and a p value <0.05 was considered statistically significant.Results: The mean serum osteocalcin concentration was 23.57ng/ml,with a standard deviation of 1.38ng/ml in the study population and decreased with age, with 24.29ng/ml in 20-44 years, 21.33ng/ml in 45-59 years and 20.69ng/ml in 60-69 years (P<0.001 for trend). The prevalence of MetS among adult males in Fangchenggang was 12.7%. Subjects with MetS had lower serum osteocalcin levels (-3.76, P<0.001) than subjects with non-MetS. Osteocalcin had a statistically significant positive correlation with HDL-c and a negative relationship with blood pressure, glucose, TG, waist circumference (WC), and BMI after adjustment for age (all P< 0.001). The strongest correlation was observed between osteocalcin and BMI (r=-0.26). In a multivariate analysis, decreased OR for the MetS and its components as well, were observed from the 1st to the 4th osteocalcin quartiles. After further adjustment for BMI, the OR decreased substantially. Statistically significant difference still existed in MetS (OR 1.77, 95% CI 1.10 to 2.85), hypertriglyceridemia (OR 1.66, 95%CI 1.22-2.27), hyperglycemia (OR 1.42, 95%CI 1.05-1.92), and low high-density lipoprotein cholesterol (OR 1.83, 95%CI 1.03-3.24), when compared these risks in the lowest quartile of osteocalcin levels with those in the highest quartile.Conclusions: In a Chinese male population, we firstly identified an inverse association of serum osteocalcin levels with MetS, independent from the well-known MetS risk factors. This may represent a further mechanism for the elevated cardiovascular disease or type 2 diabetes risk.
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