Associations Of Central Fat Accumulation With Type2Diabetes And Metabolically Obese Normal Weight Phenotype

Over the past two decades, with the rapid economic development, an accelerated pace of nutrition transition, and an increased physical inactivity, increasing rates of obesity in China are especially alarming. The rapidly increasing prevalence of obesity in China and abroad continues to be a problem of great concern and is gaining epidemic proportions. A marked increase in obesity has contributed to a tripling in diabetes incidence over the past15years in China, with the prevalence of diabetes increased from3%in1994to9.7%in2008. Surprisingly, there are a great number of people suffered from diabetes among those with normal body mass index (BMI). Despite the evidence that BMI is a key component of choice to provide a standardized definition of obesity for the purposes of national surveillance, the prevalence of obesity as defined by BMI should be interpreted cautiously as it is a poor indicator of body fat distribution. Since waist circumference (WC) is strongly correlated with central fat localization, it is a sensitive measure of central-type obesity. Evidence shows that central obesity is thought to be more pathogenic than overall obesity and the association between WC and mortality was strongest in those with a normal BMI. In addition, emerging evidence showed that significant increase in the prevalence of central obesity seems to be more pronounced than that of general obesity at given periods in both China and other countries. Furthermore, epidemiology studies indicated that a larger increase in WC may not be related to the change in BMI. Hence, even among those with normal BMI, there may be a number of people suffered from central obesity, which suggests that these individuals are predisposed to an increased risk of diabetes. The first objective of our study was to describe the secular trends in the prevalence of central obesity among Chinese adults with normal BMI from1993to2009.Visceral adiposity is independently associated with incident diabetes. Chinese individuals are characterized by a greater amount of abdominal adipose especially visceral adipose tissue than Europeans at a given BMI. Hence, even among those with relatively low BMI, there may be a lot of people present visceral adiposity accumulation, which triggers the incidence of metabolic disorder. Several prospective cohort studies have indicated that metabolically obese normal weight (MONW) phenotype exhibited increased incidences of diabetes, cardiovascular diseases, and all-cause mortality. The second objective of our study was to explore the prevalence of MONW phenotype among Chinese adults with normal BMI.The visceral adiposity is the distinguishing factor separating metabolically healthy normal weight (MHNW) individuals from MONW individuals. The magnetic resonance imaging (MRI) and computed tomography (CT) constitute the gold standard for quantitative evaluation of visceral adiposity, but the costs and radiation exposure associated with these methods represent major barriers to their widespread use in clinical practice. Recent studies shows that the lipid accumulation product (LAP) and visceral adiposity index (VAI) are two reliable indexes of central lipid accumulation that might be surrogate markers of excess visceral adiposity accumulation. Both LAP and VAI are indexes estimated with the use of both anthropometric (BMI and WC) and metabolic (triglyceride [TG] and high-density lipoprotein cholesterol [HDL-C]) parameters. Hence, LAP and VAI, simple and convenient markers of visceral obesity, are practical and acceptable. The third objective of our study was to investigate the usefulness of LAP and VAI for identifying individuals as having the MONW phenotype in persons with normal BMI.As far as we known, information on the associations of visceral adiposity indicators like VAI, LAP, and Hypertriglyceridemic waist (HTGW) with diabetes risk is scarce. Hence, the fourth objective of our study was to investigate the associations of VAI, LAP, and HTGW with risk of diabetes. Part One Increasing trends in central obesity among Chinese adults with normal body mass index,1993-2009Objective:The objective of our study was to determine secular trends in the prevalence of central obesity amongChinese adults with normal BMI from1993to2009and to examine the impact of performance of combined BMI and WC on the prevalence of obesity in Chinese adults.Methods:We used data from the China Health and Nutrition Survey (CHNS) conducted from1993to2009.From which we included a total of52023participants aged>18years. According to the International Diabetes Federation recommendations for Asians, central obesity is defined as WC≥90cm for men and≥80cm for women. The estimated prevalence was age-standardized to2000census of the Chinese adult population by the direct method.Cox proportional-hazards models were used to predict the incident hypertension and diabetes from WC within BMI categories.Results:The age-standardized prevalence of central obesity among Chinese adults with BMI<25kg/m2increased from11.9%in1993to21.1%in2009(P for linear trend <0.001). The upward trends were noted in both genders, all ages, rural/urban settings, and education groups (all P for linear trend＜O.001), with greater increments in men, participants aged18-64years, and rural residents (P for interaction terms survey x sex, survey x age, and survey x rural/urban settings were0.042,0.003, and<0.001, respectively).Trends in the prevalence of central obesity were similar when a more stringent BMI<23kg/m2cut point (Asian cut point) was applied.More than65%individuals with obesity would be missed if solely BMI was measured. Among participants with normal BMI category, the central obesity-associated hazard ratios(HR) with95%confidence intervals(CIs) forincident hypertension and diabetes werel.3(1.1-1.5) and1.8(1.4-2.5), respectively. Conclusion:We observed an upward trend in the prevalence of central obesity among participantswith normal BMI irrespective of sex, age, rural/urban settings, and education level. Central obesity is associated with a higher risk of incident hypertension and diabetes within normal BMI category.Approximately two thirds of the individuals with obesity would be missed if WC was not measured. It is, therefore, urgent to emphasize the importance of WC as a measure to monitor the prevalence of obesity and to assess the risk of obesity associated complications. Part Two Section1The prevalence of metabooically obese normal weightphenotype among participants with normal body mass indexAim:We aimed to determine the prevalence of metabolically obese normal weight (MONW) phenotype among participants with normalBMI. Moreover, we aimed to explore the association between the MONW phenotype and diabetes risk.Methods:Normal-weight participants (BMI being of18.5-23kg/m2)(n=3552) in the2009nationwide China Health and Nutrition Survey were included in our analysis. Four different criteria that have been published were used to define MONW phenotype. Odds ratios (OR) and corresponding95%confidence intervals (CI) were estimated with the use of logistic regression analysis.Results:Compared withindividuals with metabolically healthy normal weight (MHNW) phenotype, individuals withMONW phenotype exhibited poorer cardiovascular risk profile. Moreover, the metabolic disorder was more frequent in individuals with MONW phenotype. The prevalence of MONW individuals ranged from28.2%to66.8%depending on the definition used for MONW phenotype. When MHNW phenotypewas used as the reference, the crudeORs (with95%CIs) for diagnosed diabetes werel7.91(10.17-31.53),5.42(3.88-7.56),9.33(6.70-12.98), and6.73(3.96-11.44)for those with MONW phenotypes diagnosed by the Wildman criterion, Karelis criterion, ATP Ⅲdefinition of metabolic syndrom, and HOMA index, respectively.These relations were persisted even after adjustment for potential confounding variables.Conclusion:Among Chinese adults with normal BMI, there are quite a lot of people present the MONW phenotype. The MONW phenotype is an independent factor for diabetes risk. Section2Lipid accumulation product and visceral adiposity index are effective markers for identifying the metabolically obese normal weight phenotypeAim:We aimed to investigate the ability of lipid accumulation product (LAP) and visceral adiposity index (VAI), two markers of visceral obesity, to identify the MONW phenotype.Methods:Normal-weight participants (BMI being of18.5-23kg/m2)(n=3552;50.3%men) in the2009nationwide China Health and Nutrition Survey were included in our analysis. Four different criteria that have been published were used to define MONW phenotype. A receiver operating characteristic (ROC) curve analysis was performed for each adiposity measure to determine its ability to correctly discriminate MONW phenotype. ORs and corresponding95%CIs were estimated with the use of logistic regression analysis. We compared the ORs across LAP or VAI quartiles and also estimated the ORs for1standard deviation (SD) increase in LAP or VAI.Results:ROC curve analysis revealed that, regardless of the definition used to define MONW phenotype, both LAP [area under the ROC curve (AUC) ranging from0.606to0.807depending on the criteria used for MONW phenotype] and VAI (AUC ranging from0.611to0.835depending on the criteria used for MONW phenotype) outperformed the anthropometric parameters including BMI, WC, waist-to-hip ratio and waist-to-height ratio for identifying MONW phenotype. Both LAP and VAI were strongly related to MONW phenotype, irrespective of the criteria used to define the MONW phenotype. Multivariable-adjusted ORs (with95%CIs) for MONW phenotype using Wildman criterion associated with1SD increase in LAP and VAI were2.81(2.44-3.29) and9.58(7.43-12.36), respectively. When other three criteria were used to define the MONW phenotype, results were largely replicated.Conclusion:Our study demonstrates, for the first time, that both LAP and VAI are effective markers for identifying the Chinese adults with MONW phenotype. Part Three Visceral adiposity index, hypertriglyceridemic waist and lipid accumulation product and risk of diabetes:the China Health and Nutrition Survey2009Objective:We aimed to examine the association between the VAI and risk for diabetes or between the hypertriglyceridemic waist (HTGW) phenotype and diabetes risk or between the LAP and diabetes risk.Methods:We conducted a cross-sectional analysis of7639Chinese men and women aged≥18years using data from the China Health and Nutrition Survey2009. Logistic regression was used to evaluate the associations.Results:For men,compared with participants in the lowest quartile of VAI scores, the multivariable-adjusted ORs (with95%CIs) for diagnosed diabetes were1.1(0.7-1.7),1.9(1.3-2.8), and3.6(2.5-5.3) for those in the second, third, and top quartile of VAI scores, respectively. For women, the corresponding figures were0.9(0.5-1.4),1.7(1.1-2.6), and2.8(1.9-4.2), respectively.The multivariate-adjusted ORs (with95%CIs) for diabetes in men with the HTGW phenotype compared with men with both WC and TG measurements below the defined cut points were3.7(2.6-5.4). For women, the corresponding figure was3.7(2.4-5.5).For men, compared with participants in the lowest quartile of LAP scores, the multivariable-adjusted ORs (with95%CIs) for diagnosed diabetes were1.5(0.9-2.5),2.4(1.6-3.8), and4.9(3.1-7.6) for those in the second, third, and top quartile of LAP scores, respectively. For women, the corresponding figures were1.0(0.6-1.7),1.6(0.9-2.5) and3.4(2.2-5.5), respectively.For both men and women, the associations between the4th quartile of VAI scores and risk of diabetes or between the HTGW phenotype and risk of diabetesorbetween the4th quartile of LAP scoresand risk of diabetes were consistently seen in various subgroups.Conclusion:Among Chinese adults, high VAI scores, the HTGW phenotype, and LAP are strongly associated with diabetes risk.