Delineating the Relationship Between Leptin, Fat Mass, and Bone Mineral Density: A Mediation Analysis.

To test the hypothesis that the relationship between fat mass (FM) and bone mineral density (BMD) is mediated by leptin. The study involved 611 individuals aged 20-89 years who were randomly sampled from Ho Chi Minh City (Vietnam). BMD at the femoral neck (FN), lumbar spine (LS), and whole body (WB) was measured by DXA. Lean mass and FM were derived from the WB DXA scan. Leptin was measured by ELISA (DRG Diagnostics, Germany). The regression method was used to partition the variance of leptin and FM on BMD. The mediated effect of leptin was analyzed by the mediation analysis model. In the multiple linear regression, leptin, FM, and age collectively accounted for ~34 % variation in FNBMD in men and women. However, only 0.5 % of this explained variance was due to leptin. Of the total effect of FM on FNBMD, the mediated effect of leptin accounted for 6.1 % (P = 0.38) in men and 7.1 % (P = 0.99) in women. The same trend was observed for LS and WBBMD. These data suggest that greater FM is associated with greater BMD, but the association is not mediated by leptin, and that leptin has a non-significant influence on bone mass.

Reference ranges for bone mineral density and prevalence of osteoporosis in Vietnamese men and women.

BACKGROUND: The aim of this study was to examine the effect of different reference ranges in bone mineral density on the diagnosis of osteoporosis. METHODS: This cross-sectional study involved 357 men and 870 women aged between 18 and 89 years, who were randomly sampled from various districts within Ho Chi Minh City, Vietnam. BMD at the femoral neck, lumbar spine and whole body was measured by DXA (Hologic QDR4500). Polynomial regression models and bootstraps method were used to determine peak BMD and standard deviation (SD). Based on the two parameters, we computed T-scores (denoted by TVN) for each individual in the study. A similar diagnosis was also done based on T-scores provided by the densitometer (TDXA), which is based on the US White population (NHANES III). We then compared the concordance between TVN and TDXA in the classification of osteoporosis. Osteoporosis was defined according to the World Health Organization criteria. RESULTS: In post-menopausal women, the prevalence of osteoporosis based on femoral neck TVN was 29%, but when the diagnosis was based on TDXA, the prevalence was 44%. In men aged 50+ years, the TVN-based prevalence of osteoporosis was 10%, which was lower than TDXA-based prevalence (30%). Among 177 women who were diagnosed with osteoporosis by TDXA, 35% were actually osteopenia by TVN. The kappa-statistic was 0.54 for women and 0.41 for men. CONCLUSION: These data suggest that the T-scores provided by the Hologic QDR4500 over-diagnosed osteoporosis in Vietnamese men and women. This over-diagnosis could lead to over-treatment and influence the decision of recruitment of participants in clinical trials.

Discordance in the diagnosis of diabetes: Comparison between HbA1c and fasting plasma glucose.

OBJECTIVE: HbA1c has been introduced as a complementary diagnostic test for diabetes, but its impact on disease prevalence is unknown. This study evaluated the concordance between HbA1c and fasting plasma glucose (FPG) in the diagnosis of diabetes in the general population. MATERIALS AND METHODS: The study was designed as a population based investigation, with participants being sampled from the Ho Chi Minh City, Vietnam. Blood samples were collected after overnight fasting and analyzed within 4 hours after collection. HbA1c was measured with high pressure liquid chromatography (Arkray Adams, Japan). FPG was measured by the hexokinase method (Advia Autoanalyzer; Bayer Diagnostics, Germany). Diabetes was defined as HbA1c ≥ 6.5% or FPG ≥ 7.0 mmol/L. Prediabetes was classified as HbA1c between 5.7% and 6.4%. RESULTS: The study included 3523 individuals (2356 women) aged 30 years and above. Based on the HbA1c test, the prevalence of diabetes and prediabetes was 9.7% (95%CI, 8.7-10.7%; n = 342) and 34.6% (33.0-36.2; n = 1219), respectively. Based on the FPG test, the prevalence of diabetes and prediabetes was 6.3% (95%CI, 5.5-7.2%; n = 223) and 12.1% (11.1-13.2; n = 427). Among the 427 individuals identified by FPG as "pre-diabetes", 28.6% were classified as diabetes by HbA1c test. The weighted kappa statistic of concordance between HbA1c and FPG was 0.55, with most of the discordance being in the prediabetes group. CONCLUSION: These data indicate that there is a significant discordance in the diagnosis of diabetes between FPG and HbA1c measurements, and the discordance could have significant impact on clinical practice. FPG appears to underestimate the burden of undiagnosed diabetes.

Association between lean mass, fat mass, and bone mineral density: a meta-analysis.

CONTEXT: Body weight is the most important anthropometric determinant of bone mineral density (BMD). Body weight is mainly made up of lean mass (LM) and fat mass (FM), and which component is more important to BMD has been a controversial issue. OBJECTIVE: This study sought to compare the magnitude of association between LM, FM, and BMD by using a meta-analytic approach. DATA SOURCE: Using an electronic and manual search, we identified 44 studies that had examined the correlation between LM, FM, and BMD between 1989 and 2013. These studies involved 20,226 men and women (4966 men and 15,260 women) aged between 18 and 92 years. We extracted the correlations between LM, FM, and BMD at the lumbar spine, femoral neck, and whole body. The synthesis of correlation coefficients was done by the random-effects meta-analysis model. RESULTS: The overall correlation between LM and femoral neck BMD (FNBMD) was 0.39 (95% confidence interval, 0.34 to 0.43), which was significantly higher than the correlation between FM and FNBMD (0.28; 95% confidence interval, 0.22 to 0.33). The effect of LM on FNBMD in men (r=0.43) was greater than that in women (r=0.38). In premenopausal women, the effect of LM on BMD was greater than the effect of FM (r=0.45 vs r=0.30); however, in postmenopausal women, the effects of LM and FM on BMD were comparable (r=0.33 vs r=0.31). CONCLUSION: LM exerts a greater effect on BMD than FM in men and women combined. This finding underlines the concept that physical activity is an important component in the prevention of bone loss and osteoporosis in the population.