Cardiorespiratory Fitness, Body Mass Index, and Markers of Insulin Resistance in Apparently Healthy Women and Men

BACKGROUND

Insulin resistance may be present in healthy adults and is associated with poor health outcomes. Obesity is a risk factor for insulin resistance, but most obese adults do not have insulin resistance. Fitness may be protective, but the association between fitness, weight, and insulin resistance has not been studied in a large population of healthy adults.

METHODS

A cross-sectional analysis of cardiorespiratory fitness, body mass index, and markers of insulin resistance was performed. Study participants were enrolled at the Cooper Clinic in Dallas, Texas. The analysis included 19,263 women and 48,433 men with no history of diabetes or cardiovascular disease. Cardiorespiratory fitness was measured using exercise treadmill testing. Impaired fasting glucose (100-125 mg/dL) and elevated fasting triglycerides (≥150 mg/dL) were used as a markers of insulin resistance.

RESULTS

Among individuals with normal weight, poor fitness was associated with 2.2-fold higher odds of insulin resistance in women (1.4-3.6; P = .001) and 2.8-fold higher odds in men (2.1-3.6; P <.001). The impact of fitness remained significant for overweight and obese individuals, with the highest risk group being the unfit obese. Among obese women, the odds ratio for insulin resistance was 11.0 for fit women (8.7-13.9; P <.001) and 20.3 for unfit women (15.5-26.5; P <.001). Among obese men, the odds ratio for insulin resistance was 7.4 for fit men (6.7-8.2; P < .001) and 12.9 for unfit men (11.4-14.6; P < .001).

CONCLUSIONS

Independent of weight, poor fitness is associated with risk of insulin resistance. Obese individuals, particularly women, may benefit from the greatest absolute risk reduction by achieving moderate fitness.

Plasma glucose concentration 60 min post oral glucose load and risk of type 2 diabetes and cardiovascular disease: Pathophysiological implications

AIM

The aim of this study was to gain insight into the pathophysiological significance of elevated plasma glucose concentrations (mmol/L) 60 min post oral glucose load in apparently healthy individuals.

METHODS

Comparison of resistance to insulin action and associated cardio-metabolic risk factors in 490 apparently healthy persons, subdivided into those with a plasma glucose concentration 60 min following a 75-g oral glucose challenge of <8.6 versus ⩾8.6.

RESULTS

Insulin resistance was significantly greater in persons with normal glucose tolerance whose 60-min glucose concentration was ⩾8.6, associated with higher blood pressure, plasma concentrations of glucose, insulin, triglyceride and lower high-density lipoprotein cholesterol concentrations. Similar differences were seen in persons with impaired fasting glucose, but not in those with impaired glucose tolerance or both impaired fasting glucose and impaired glucose tolerance. The group whose 60-min glucose was <8.6 (n = 318) contained primarily persons with normal glucose tolerance (88%), whereas the majority of those whose 60-min value was ⩾8.6 (n = 172) had prediabetes (59%) and in particular combined impaired fasting glucose and impaired glucose tolerance.

CONCLUSION

Plasma glucose concentration of ⩾8.6 mmol/L 60 min post oral glucose identifies higher proportions of combined impaired fasting glucose and impaired glucose tolerance individuals as well as normal glucose tolerance and impaired fasting glucose individuals with a more adverse cardio-metabolic profile, contributing to observed increased overall risk of type 2 diabetes and other metabolic diseases.

Impact of race/ethnicity on insulin resistance and hypertriglyceridaemia

OBJECTIVE

Insulin sensitivity affects plasma triglyceride concentration and both differ by race/ethnicity. The purpose of this study was to provide a comprehensive assessment of the variation in insulin sensitivity and its relationship to hypertriglyceridaemia between five race/ethnic groups.

RESEARCH DESIGN AND METHODS

In this cross-sectional study, clinical data for 1025 healthy non-Hispanic White, Hispanic White, East Asian, South Asian and African American individuals were analysed. Insulin-mediated glucose disposal (a direct measure of peripheral insulin sensitivity) was measured using the modified insulin suppression test. Statistical analysis was performed using analysis of co-variance.

RESULTS

Of the study participants, 63% were non-Hispanic White, 9% were Hispanic White, 11% were East Asian, 11% were South Asian and 6% were African American. Overall, non-Hispanic Whites and African Americans displayed greater insulin sensitivity than East Asians and South Asians. Triglyceride concentration was positively associated with insulin resistance in all groups, including African Americans. Nevertheless, for any given level of insulin sensitivity, African Americans had the lowest triglyceride concentrations.

CONCLUSION

Insulin sensitivity, as assessed by a direct measure of insulin-mediated glucose disposal, and its relationship to triglyceride concentration vary across five race/ethnic groups. Understanding these relationships is crucial for accurate cardiovascular risk stratification and prevention.

Can the Plasma Concentration Ratio of Triglyceride/High-Density Lipoprotein Cholesterol Identify Individuals at High Risk of Cardiovascular Disease During 40-Year Follow-Up?

BACKGROUND

The plasma concentration ratio of triglyceride (TG)/high-density lipoprotein cholesterol (HDL-C) is a simple way to estimate insulin resistance. We aimed to evaluate the TG/HDL-C ratio as a simple clinical way to identify apparently healthy individuals with insulin resistance and enhanced risk of future cardiovascular disease (CVD).

METHODS

One thousand seven hundred twenty men, aged 50 years, free from diabetes and CVD when evaluated at baseline in 1970-1974 were followed for 40 years regarding incident CVD (myocardial infarction and/or ischemic stroke, n = 576).

RESULTS

Participants with a high TG/HDL-C ratio (highest quartile >1.8) at baseline were more insulin resistant, with a significantly more adverse cardiometabolic risk profile (P < 0.001) at baseline, compared with those with a lower ratio. This group also showed an increased risk of CVD [hazard ratio, HR 1.47 (95% confidence interval 1.26-1.93) P < 0.001]. Fourteen percent of subjects with metabolic syndrome, in whom insulin resistance is increased, were also at enhanced CVD risk [HR 1.75 (1.42-2.16) P < 0.001].

CONCLUSIONS

Twenty-five percent of apparently healthy 50-year-old men with the highest TG/HDL-C plasma concentration ratio had a significantly more adverse cardiometabolic profile at baseline, and developed more CVD over the next 40 years, compared with those not meeting this cut point. Determining the TG/HDL-C ratio in middle-aged men provided a simple and potentially clinically useful way to identify increased risk of developing CVD in persons free of diabetes or manifest CVD.

Adapting to insulin resistance in obesity: role of insulin secretion and clearance

AIMS/HYPOTHESIS

The aim of this study was to quantify the relative contributions of increased insulin secretion rate (ISR) and decreased insulin clearance rate (ICR) in the compensatory hyperinsulinaemia characteristic of insulin-resistant individuals without diabetes.

METHODS

Obese (BMI ≥30 kg/m²) individuals without diabetes (n = 91) were identified from a registry of volunteers. Volunteers underwent the following measurements: oral glucose tolerance; insulin resistance (steady-state plasma glucose [SSPG] concentration during the insulin suppression test [IST]); ISR (using the graded glucose infusion test [GGIT]); and ICR (using the IST and GGIT). Participants were stratified into tertiles based on SSPG concentration: SSPG-1(insulin-sensitive); SSPG-2 (intermediate); and SSPG-3 (insulin-resistant).

RESULTS

There were no differences in BMI and waist circumference among the SSPG tertiles. Serum alanine aminotransferase concentrations were higher in the SSPG-2 and SSPG-3 groups compared with the SSPG-1 group (p = 0.02). Following an oral glucose challenge, there was a progressive increase in the total integrated insulin response from the most insulin-sensitive to the most insulin-resistant tertiles (p < 0.001). Following intravenous glucose, the SSPG-3 group had significantly greater integrated glucose (median [interquartile range], 32.9 [30.8-36.3] mmol/l × h) and insulin responses (1711 [1476-2223] mmol/l × h) compared with the SSPG-1 group (30.3 [28.8-32.9] mmol/l × h, p = 0.04, and 851 [600-1057] pmol/l × h, p < 0.001, respectively). Furthermore, only the SSPG-3 group had significant changes in both ISR and ICR (p < 0.001). In the SSPG-2 group, only the ICR was significantly decreased compared with the SSPG-1 group. Therefore, ICR progressively declined during the IST with increasing insulin resistance (SSPG-1, 0.48 [0.41-0.59]; SSPG-2, 0.43 [0.39-0.50]; SSPG-3, 0.34 [0.31-0.40]).

CONCLUSIONS/INTERPRETATION

While both increases in ISR and decreases in ICR compensate for insulin resistance, decreases in ICR may provide the first adaptation to decreased insulin sensitivity.

Relationship between several surrogate estimates of insulin resistance and a direct measure of insulin-mediated glucose disposal: Comparison of fasting versus post-glucose load measurements

AIMS

The study aim was to determine the correlation of several surrogate estimates of insulin resistance with a direct measure of insulin action and the ability of these estimates to identify insulin resistant persons.

METHODS

Retrospective analysis of 454 apparently healthy individuals studied in a clinical research center. The correlations between 11 surrogate estimates of insulin resistance, using either fasting or post-oral glucose challenge values, and a direct measure of insulin-mediated glucose uptake (SSPG concentration during the Insulin Suppression Test) were determined as well as the ability of the surrogate estimates to identify insulin resistant individuals.

RESULTS

All surrogate estimates were significantly (P < .001) correlated with SSPG concentrations and successfully identified insulin resistant persons. These relationships were of lesser magnitude when estimates were based on fasting data, with the exception of the McAuley index-derived from fasting data, but resembling post-glucose challenge estimates. Moreover, correlation with SSPG concentration, and positive identification of insulin resistance, varied considerably among estimates.

CONCLUSION

All 11 surrogate estimates of insulin resistance significantly correlated with insulin-mediated glucose disposal and identified insulin resistant persons with a reasonable degree of sensitivity and specificity. For identification of insulin resistant individuals, indices based on post-glucose challenge measurements performed better than those based on fasting measurements, with the exception of McAuley index. The quantitative information derived from this analysis should help investigators select the surrogate marker of insulin resistance best suited for their study.

Relationship between simple markers of insulin resistance and coronary artery calcification

BACKGROUND

Insulin resistance in apparently healthy persons is associated with a cluster of metabolic abnormalities that promote coronary atherosclerosis. Identifying these individuals before manifest disease would provide useful clinical information.

OBJECTIVE

We hypothesized that combining 2 simple markers of insulin resistance, prediabetes (PreDM) and triglyceride (TG) concentration ≥150 mg/dL, would identify apparently healthy persons with adverse cardiometabolic risk profiles and increased coronary artery calcium (CAC) compared with those with neither or only 1 abnormality.

METHODS

A cross-sectional analysis was performed using data from 25,886 apparently healthy individuals (18,453 men and 7433 women) evaluated at the Cooper Clinic from 1998 to 2015. Participants were divided into those with a normal fasting glucose concentrations (<100 mg/dL = normal fasting glucose) or PreDM (fasting plasma glucose ≥100 and <126 mg/dL) and further subdivided into those with a plasma TG concentration <150 or ≥150 mg/dL. These 4 groups were compared on the basis of multiple coronary artery disease risk factors and the presence of CAC determined during their evaluation.

RESULTS

Participants with PreDM and a TG concentration ≥150 mg/dL had a significantly more adverse coronary artery disease risk profile than individuals with either abnormality or only 1 abnormality (PreDM or TG concentration ≥150 mg/dL). Furthermore, the odds of detectable CAC were higher in participants with PreDM and a TG ≥ 150 mg/dL than in participants with neither or only 1 abnormality.

CONCLUSION

The presence of 2 markers of insulin resistance, PreDM and TG concentration ≥150 mg/dL, is associated with increased cardiometabolic risk and detectable CAC within a population of apparently healthy individuals.

Effect of Pioglitazone on Cardiometabolic Risk in Patients With Obstructive Sleep Apnea

Prevalence of insulin resistance is increased in patients with obstructive sleep apnea (OSA). Because insulin resistance is an independent predictor of cardiovascular disease (CVD), this study was initiated to see if pioglitazone administration would improve insulin sensitivity and thereby decrease risk of CVD in overweight/obese, nondiabetic, insulin-resistant patients with untreated OSA. Patients (n = 30) were administered pioglitazone (45 mg/day) for 8 weeks, and measurements were made before and after intervention of insulin action (insulin-mediated glucose uptake by the insulin suppression test), C-reactive protein, lipid/lipoprotein profile, and gene expression profile of periumbilical subcutaneous fat tissue. Insulin sensitivity increased 31% (p <0.001) among pioglitazone-treated subjects, associated with a decrease in C-reactive protein concentration (p ≤0.001), a decrease in plasma triglyceride, and increase in high-density lipoprotein cholesterol concentrations (p ≤0.001), accompanied by significant changes in apolipoprotein A1 and B concentrations and lipoprotein subclasses known to decrease CVD risk. In addition, subcutaneous adipose tissue gene expression profile showed a 1.6-fold (p <0.01) increase in GLUT4 expression and decreased expression in 5 of 9 inflammatory genes (p <0.05). In conclusion, enhanced insulin sensitivity can significantly decrease multiple cardiometabolic risk factors in patients with untreated OSA, consistent with the view that coexisting insulin resistance plays an important role in the association between OSA and increased risk of CVD.

Relationship among age, insulin resistance, and blood pressure

The effect of age to modify the relationship between insulin resistance and hypertension is unclear. In this retrospective, cross-sectional study, median age was used to create two age groups (<52 vs. ≥52 years), and comparisons were made of metabolic characteristics, including steady-state plasma glucose (SSPG) concentrations measured during the insulin suppression test to quantify insulin resistance. Individuals were stratified into SSPG tertiles and categorized as having normal blood pressure (BP), prehypertension, or hypertension. SSPG concentrations were similar in the two age groups (161 vs. 164 mg/dL). In the most insulin-resistant tertile, distribution of normal BP, prehypertension, and hypertension was equal in those aged <52 years, whereas in those aged ≥52 years, prevalence of hypertension was increased approximately fivefold compared with those with normal BP. Multivariate regression analysis demonstrated significant interaction between age and SSPG in predicting systolic BP (P = .023). In stratified analysis, SSPG, but not age, was an independent predictor of systolic BP and diastolic BP in ≥52 years group, whereas the reverse was true in the younger group. The adverse impact of insulin resistance on BP was accentuated in older individuals and may have a greater impact than further aging.

Comparison of two surrogate estimates of insulin resistance to predict cardiovascular disease in apparently healthy individuals

BACKGROUND AND AIMS

Insulin resistance is associated with a cluster of abnormalities that increase cardiovascular disease (CVD). Several indices have been proposed to identify individuals who are insulin resistant, and thereby at increased CVD risk. The aim of this study was to compare the abilities of 3 indices to accomplish that goal: 1) plasma triglyceride × glucose index (TG × G); 2) plasma triglyceride/high-density lipoprotein cholesterol ratio (TG/HDL-C); and 3) Metabolic Syndrome (MetS).

METHODS AND RESULTS

In a population sample of 723 individuals (486 women and 237 men, 50 ± 16 and 51 ± 16 years old, respectively), baseline demographic and metabolic variables known to increase CVD risk and incident CVD were compared among individuals defined as high vs. low risk by: TG × G; TG/HDL-C; or MetS. CVD risk profiles appeared comparable in high risk subjects, irrespective of criteria. Crude incidence of CVD events was increased in high risk subjects: 12.2 vs. 5.3% subjects/10 years, p = 0.005 defined by TG/HDL-C; 13.4 vs. 5.3% subjects/10 years, p = 0.002 defined by TG × G; and 13.4% vs. 4.5% of subjects/10 years, p < 0.001 in subjects with the MetS. The area under the ROC curves to predict CVD were similar, 0.66 vs. 0.67 for TG/HDL-C and TG × G, respectively. However, when adjusted by age, sex and multiple covariates, hazard ratios for incident CVD were significantly increased in high risk patients classified by either TG/HDL-C ratio (2.18, p = 0.021) or MetS (1.93, p = 0.037), but not by TG × G index (1.72, p = 0.087).

CONCLUSION

Although the 3 indices identify CVD risk comparably, the TG × G index seems somewhat less effective at predicting CVD.

Dissecting the relationship between obesity and hyperinsulinemia: Role of insulin secretion and insulin clearance

OBJECTIVE

The aim of this study was to better delineate the complex interrelationship among insulin resistance (IR), secretion rate (ISR), and clearance rate (ICR) to increase plasma insulin concentrations in obesity.

METHODS

Healthy volunteers (92 nondiabetic individuals) had an insulin suppression test to measure IR and graded-glucose infusion test to measure ISR and ICR. Obesity was defined as a body mass index (BMI) ≥30 kg/m² , and IR was defined as steady-state plasma glucose (SSPG) ≥10 mmol/L during the insulin suppression test. Plasma glucose and insulin concentrations, ISR, and ICR were compared in three groups: insulin sensitive/overweight; insulin sensitive/obesity; and insulin resistant/obesity.

RESULTS

Compared with the insulin-sensitive/overweight group, the insulin-sensitive/obesity had significantly higher insulin area under the curve (AUC) and ISR AUC during the graded-glucose infusion test (P < 0.001). Glucose AUC and ICR were similar. The insulin-resistant/obesity group had higher insulin AUC and ISR AUC compared with the insulin-sensitive/obesity but also had higher glucose AUC and decreased ICR (P < 0.01). In multivariate analysis, both BMI and SSPG were significantly associated with ISR.

CONCLUSIONS

Plasma insulin concentration and ISR are increased in individuals with obesity, irrespective of degree of IR, but a decrease in ICR is confined to the subset of individuals with IR.

Hypertriglyceridemia: A simple approach to identify insulin resistance and enhanced cardio-metabolic risk in patients with prediabetes

AIMS

Prediabetes (PreDM) is a metabolically heterogeneous condition, differing in degree of insulin resistance and risk of type 2 diabetes mellitus and coronary heart disease (CHD). This study was initiated to evaluate the hypothesis that a fasting plasma triglyceride (TG) concentration ⩾1.7mmol/L can aid in identifying the subset of individuals with PreDM who are most insulin resistant and at greatest risk to develop CHD as well as type 2 diabetes mellitus.

METHODS

In this cross-sectional study, measurements were made of: (1) steady-state plasma glucose (SSPG) concentration during the insulin suppression test to ascertain degree of insulin resistance and (2) conventional CHD risk factors in 587 apparently healthy individuals with normal fasting plasma glucose (NFG, n=370) or PreDM (n=217).

RESULTS

Subjects with PreDM were significantly (P<0.001) more insulin resistant (higher SSPG concentrations) and had a more adverse CHD risk profile than those with NFG. A TG concentration ⩾1.7mmol/L identified a subset of individuals with PreDM (38%) who had a higher mean SSPG concentration (11.3±3.5mmol/L vs. 9.3±3.9mmol/L, P<0.001), were more likely to be insulin resistant (66% vs. 39%, P<0.001), and had a more adverse CHD risk factor profile.

CONCLUSIONS

Measurement of fasting TG concentration in individuals with PreDM may provide a simple clinical approach to identify those who are insulin resistant, at enhanced risk of CHD, and more likely to develop type 2 diabetes mellitus.

Use of the triglyceride/high-density lipoprotein cholesterol ratio to identify cardiometabolic risk: impact of obesity?

There is evidence that the plasma concentration ratio of triglyceride (TG)/high-density lipoprotein cholesterol (HDL-C) identifies insulin resistance and increased cardiometabolic risk and outcome in apparently healthy individuals. Since use of the TG/HDL-C ratio to accomplish this task in persons over a wide range of adiposity has not been studied, the ability of previously defined sex-specific TG/HDL-C cut-points to identify increased cardiometabolic risk was evaluated in apparently healthy normal weight, overweight, and obese individuals. Data were analyzed from a population-based study of apparently healthy men (n=416) and women (n=893), subdivided into categories by body mass index (BMI, kg/m2): normal weight (BMI 20.0–24.9), overweight (BMI 25.0–29.9) and obese (BMI 30.0–34.9). The adiposity groups were further stratified on the basis of their TG/HDL-C ratio into groups defined as being either at ‘high risk’ versus ‘low risk’ of cardiometabolic disease. Multiple cardiometabolic risk factors were compared between these subgroups, as was their degree of insulin resistance assessed by fasting plasma insulin concentration and homeostasis model assessment of insulin resistance. The proportion of high-risk individuals varied with BMI category, ranging from 14% (normal weight) to 36% (obese). However, within each BMI category high-risk individuals had a significantly more adverse cardiometabolic risk profile. Finally, the adjusted OR of being insulin resistant was significantly greater in those with a high TG/HDL-C ratio in the normal (3.02), overweight (2.86), and obese (2.51) groups. Thus, irrespective of differences in BMI, the TG/HDL-C ratio identified apparently healthy persons with a more adverse cardiometabolic risk profile associated with an increased prevalence of insulin resistance.

Relationship between insulin sensitivity and insulin secretion rate: not necessarily hyperbolic

AIMS

There is general acceptance that the physiological relationship between insulin sensitivity and insulin secretion is hyperbolic. This conclusion has evolved from studies in which one test assessed both variables, and changes in plasma insulin concentration were used as a surrogate measure for insulin secretion rate. The aim of this study was to see if a hyperbolic relationship would also emerge when separate and direct measures were used to quantify both insulin sensitivity and insulin secretion rate.

METHODS

Steady-state plasma glucose (SSPG) was determined in 146 individuals without diabetes using the insulin suppression test, with 1/SSPG used to quantify insulin sensitivity. The graded-glucose infusion test was used to quantify insulin secretion rate. Plasma glucose and insulin concentrations obtained during an oral glucose tolerance test (OGTT) were used to calculate surrogate estimates of insulin action and insulin secretion rate. A hyperbolic relationship was assumed if the β coefficient was near -1 using the following model: log (insulin secretion measure) = constant + β × log (insulin sensitivity measure).

RESULTS

OGTT calculations of insulin sensitivity (Matsuda) and plasma insulin response [ratio of insulin/glucose area-under-the-curve (AUC) or insulin total AUC] provided the expected hyperbolic relationship [β = -0.95, 95% CI (-1.09, -0.82); -1.06 (-1.14, -0.98)]. Direct measurements of insulin sensitivity and insulin secretion rate did not yield the same curvilinear relationship [β = -1.97 (-3.19, -1.36)].

CONCLUSIONS

These findings demonstrate that the physiological relationship between insulin sensitivity and insulin secretion rate is not necessarily hyperbolic, but will vary with the method(s) by which it is determined.

Insulin clearance: an underappreciated modulator of plasma insulin concentration

Plasma glucose concentrations are tightly regulated and maintained within a narrow range in non-diabetic individuals. Maintenance of this physiological state is primarily a function of the ability of the pancreatic β-cells to modify insulin secretion rate (ISR), thus preventing wide-swings in plasma glucose concentrations. As a consequence, and in contrast to plasma glucose concentrations, plasma insulin concentrations vary substantially in non-diabetic individuals. Although differences in ISR are primarily responsible for the variability in plasma insulin concentration, there is increasing evidence that differences in insulin clearance rate (ICR) also play a role in regulation of plasma insulin concentration. The goal of this mini-review is to highlight situations that demonstrate the important role of ICR in both insulin and glucose homeostasis.

Cardiometabolic Risk in South Asian Inhabitants of California: Hypertriglyceridemic Waist vs Hypertriglyceridemic Body Mass Index

OBJECTIVE

Hypertriglyceridemic waist (HTG-waist), an increased waist circumference (WC) with an elevated triglyceride (TG) concentration, can identify increased cardiometabolic risk in apparently healthy individuals. Since WC and BMI are highly correlated, we examined whether an HTG-BMI would be as effective as an HTG-waist in identifying cardiometabolic risk in apparently healthy South Asians.

DESIGN SETTING AND PARTICIPANTS

In this cross-sectional study, we classified South Asian women (n=1156) and men (n=1842) without diabetes mellitus as having an HTG-waist (TG ≥150 mg/dL and a WC ≥80 cm in women or ≥ 90 cm in men) and an HTG-BMI (TG ≥150 mg/dL and a BMI ≥23 kg/m²).

OUTCOME MEASURES

We measured cardiometabolic risk factors, including blood pressure and fasting lipid profile, glucose, insulin, fibrinogen, and high-sensitivity C-reactive protein.

RESULTS

An HTG-waist was present in 670 individuals, of whom 648 (97%) had an HTG-BMI. The cardiometabolic profile was significantly more adverse in those in whom an HTG-waist was present vs absent; and the same was true when individuals with an HTG-BMI were compared with those without.

CONCLUSIONS

Essentially every individual with an HTG-waist also had an HTG-BMI. An HTG-BMI identified cardiometabolic risk as effectively as an HTG-waist in a population composed entirely of South Asians.

Insulin resistance: The linchpin between prediabetes and cardiovascular disease

The aim of this study was to test the hypothesis that cardiovascular disease occurs to the greatest extent in persons with prediabetes mellitus who are also insulin resistant. In 2003, 664 non-diabetic women (n = 457) and men (n = 207), aged 52 ± 16 and 53 ± 15 years, were surveyed during a programme for cardiovascular disease prevention. Fasting plasma glucose concentrations defined participants as having normal fasting plasma glucose (fasting plasma glucose <5.6 mmol/L) or prediabetes mellitus (fasting plasma glucose ⩾ 5.6 and <7.0 mmol/L). The tertile of prediabetes mellitus subjects with the highest fasting plasma insulin concentration was classified as insulin resistant. Baseline cardiovascular disease risk factors were accentuated in prediabetes mellitus versus normal fasting glucose, particularly in prediabetes mellitus/insulin resistant. In 2012, 86% of the sample were surveyed again, and the crude incidence for cardiovascular disease was higher in subjects with prediabetes mellitus versus normal fasting glucose (13.7 vs 6.0/100 persons/10 years; age- and sex-adjusted hazard ratio = 1.88, p = 0.052). In prediabetes mellitus, the crude incidences were 22.9 versus 9.6/100 persons/10 years in insulin resistant versus non-insulin resistant persons (age- and sex-adjusted hazard ratio = 2.36, p = 0.040). In conclusion, cardiovascular disease risk was accentuated in prediabetes mellitus/insulin resistant individuals, with a relative risk approximately twice as high compared to prediabetes mellitus/non-insulin resistant subjects.

Use of plasma triglyceride/high-density lipoprotein cholesterol ratio to identify increased cardio-metabolic risk in young, healthy South Asians

Background & objectives:

Prevalence of insulin resistance and associated dyslipidaemia [high triglyceride (TG) and low high-density lipoprotein cholesterol (HDL-C) concentrations] are increased in South Asian individuals; likely contributing to their increased risk of type-2 diabetes and cardiovascular disease. The plasma concentration ratio of TG/HDL-C has been proposed as a simple way to identify apparently healthy individuals at high cardio-metabolic risk. This study was carried out to compare the cardio-metabolic risk profiles of high-risk South Asian individuals identified by an elevated TG/HDL-C ratio versus those with a diagnosis of the metabolic syndrome.

Methods:

Body mass index, waist circumference, blood pressure, and fasting plasma glucose, insulin, TG, and HDL-C concentrations were determined in apparently healthy men (n=498) and women (n=526). The cardio-metabolic risk profile of “high risk” individuals identified by TG/HDL-C ratios in men (≥ 3.5) and women (≥2.5) was compared to those identified by a diagnosis of the metabolic syndrome.

Results:

More concentrations of all cardio-metabolic risk factors were significantly higher in “high risk” groups, identified by either the TG/HDL-C ratio or a diagnosis of the metabolic syndrome. TG, HDL-C, and insulin concentrations were not significantly different in “high risk” groups identified by either criterion, whereas plasma glucose and blood pressure were higher in those with the metabolic syndrome.

Interpretation & conclusions:

Apparently healthy South Asian individuals at high cardio-metabolic risk can be identified using either the TG/HDL-C ratio or the metabolic syndrome criteria. The TG/HDL-C ratio may be used as a simple marker to identify such individuals.

Hyperinsulinemia in individuals with obesity: Role of insulin clearance

OBJECTIVE

Several studies have shown decreased insulin clearance rate (ICR) in individuals with obesity, but it remains unclear whether this is predominately due to obesity-associated insulin resistance (IR) or obesity itself. This study aimed to clarify the complex interrelationship that exists between obesity, IR, and ICR.

METHODS

Healthy volunteers (n = 277) had measurement of IR and ICR using the insulin suppression test (IST). IR was quantified by determining the steady-state plasma glucose (SSPG) during the IST. ICR was estimated by dividing the insulin infusion rate by the steady-state plasma insulin concentration. We performed our analysis by stratifying the experimental population into four dichotomous categories, varying in obesity and IR. Obesity was defined as a body mass index (BMI) ≥ 30 kg/m(2) , and IR was defined as SSPG ≥ 150 mg/dL.

RESULTS

Individuals with obesity had higher fasting insulin compared with individuals without obesity, regardless of IR. ICR was similar between individuals with and without obesity but was higher in insulin resistant individuals compared with insulin-sensitive individuals. In multivariate analysis, both fasting insulin and SSPG were significantly associated with ICR. No significant relationships were observed between BMI and ICR.

CONCLUSIONS

Reduced ICR in obesity is secondary to IR, not excess adiposity.

Circulating microRNA-320a and microRNA-486 predict thiazolidinedione response: Moving towards precision health for diabetes prevention

INTRODUCTION

The aims of this study were to compare microRNA (miR) expression between individuals with and without insulin resistance and to determine whether miRs predict response to thiazolidinedione treatment.

MATERIALS AND METHODS

In a sample of 93 healthy adults, insulin resistance was defined as steady state plasma glucose (SSPG)≥180 mg/dL and insulin sensitive as <120 mg/dL. Response to thiazolidinedione therapy was defined as ≥10% decrease in SSPG. We selected a panel of microRNAs based on prior evidence for a role in insulin or glucose metabolism. Fold change and Wilcoxon rank sum tests were calculated for the 25 miRs measured.

RESULTS

At baseline, 81% (n=75) of participants were insulin resistant. Five miRs were differentially expressed between the insulin resistant and sensitive groups: miR-193b (1.45 fold change (FC)), miR-22-3p (1.15 FC), miR-320a (1.36 FC), miR-375 (0.59 FC), and miR-486 (1.21 FC) (all p<0.05). In the subset who were insulin resistant at baseline and received thiazolidinediones (n=47), 77% (n=36) showed improved insulin sensitivity. Six miRs were differentially expressed between responders compared to non-responders: miR-20b-5p (1.20 FC), miR-21-5p, (0.92 FC), miR-214-3p (1.13 FC), miR-22-3p (1.14 FC), miR-320a (0.98 FC), and miR-486-5p (1.25 FC) (all p<0.05).

DISCUSSION

This study is the first to report miRs associated with response to a pharmacologic intervention for insulin resistance. MiR-320a and miR-486-5p identified responders to thiazolidinedione therapy among the insulin resistant group.

Abnormalities of lipoprotein concentrations in obstructive sleep apnea are related to insulin resistance

STUDY OBJECTIVE

Prevalence of cardiovascular disease (CVD) is increased in patients with obstructive sleep apnea (OSA), possibly related to dyslipidemia in these individuals. Insulin resistance is also common in OSA, but its contribution to dyslipidemia of OSA is unclear. The study's aim was to define the relationships among abnormalities of lipoprotein metabolism, clinical measures of OSA, and insulin resistance.

DESIGN

Cross-sectional study. OSA severity was defined by the apnea-hypopnea index (AHI) during polysomnography. Hypoxia measures were expressed as minimum and mean oxygen saturation, and the oxygen desaturation index. Insulin resistance was quantified by determining steady-state plasma glucose (SSPG) concentrations during the insulin suppression test. Fasting plasma lipid/lipoprotein evaluation was performed by vertical auto profile methodology.

SETTING

Academic medical center.

PARTICIPANTS

107 nondiabetic, overweight/obese adults.

MEASUREMENTS AND RESULTS

Lipoprotein particles did not correlate with AHI or any hypoxia measures, nor were there differences noted by categories of OSA severity. By contrast, even after adjustment for age, sex, and BMI, SSPG was positively correlated with triglycerides (r = 0.30, P < 0.01), very low density lipoprotein (VLDL) and its subclasses (VLDL1+2) (r = 0.21-0.23, P < 0.05), and low density lipoprotein subclass 4 (LDL4) (r = 0.30, P < 0.01). SSPG was negatively correlated with high density lipoprotein (HDL) (r = -0.38, P < 0.001) and its subclasses (HDL2 and HDL3) (r = -0.32, -0.43, P < 0.01), and apolipoprotein A1 (r = -0.33, P < 0.01). Linear trends of these lipoprotein concentrations across SSPG tertiles were also significant.

CONCLUSIONS

Pro-atherogenic lipoprotein abnormalities in obstructive sleep apnea (OSA) are related to insulin resistance, but not to OSA severity or degree of hypoxia. Insulin resistance may represent the link between OSA-related dyslipidemia and increased cardiovascular disease risk.

Low circulating 25-hydroxyvitamin D concentrations are associated with defects in insulin action and insulin secretion in persons with prediabetes

BACKGROUND

Individuals with prediabetes mellitus (PreDM) and low circulating 25-hydroxyvitamin D [25(OH)D] are at increased risk of type 2 diabetes mellitus (T2DM).

OBJECTIVE

We aimed to determine whether low 25(OH)D concentrations are associated with defects in insulin action and insulin secretion in persons with PreDM.

METHODS

In this cross-sectional study, we stratified 488 nondiabetic subjects as having PreDM or normal fasting glucose (NFG) and a 25(OH)D concentration ≤20 ng/mL (deficient) or >20 ng/mL (sufficient). We determined insulin resistance by steady state plasma glucose (SSPG) concentration and homeostasis model assessment of insulin resistance (HOMA-IR) and insulin secretion by homeostasis model assessment of β-cell function (HOMA-β). We compared insulin resistance and secretion measures in PreDM and NFG groups; 25(OH)D-deficient and 25(OH)D-sufficient groups; and PreDM-deficient, PreDM-sufficient, NFG-deficient, and NFG-sufficient subgroups, adjusting for age, sex, race, body mass index, multivitamin use, and season.

RESULTS

In the PreDM group, mean SSPG concentration and HOMA-IR were higher and mean HOMA-β was lower than in the NFG group (P < 0.001 for all comparisons). In the 25(OH)D-deficient group, mean SSPG concentration was higher (P < 0.001), but neither mean HOMA-IR nor HOMA-β was significantly different from that in the 25(OH)D-sufficient group. In the PreDM-deficient subgroup, mean (95% CI) SSPG concentration was higher (P < 0.01) than in the PreDM-sufficient, NFG-deficient, and NFG-sufficient subgroups [192 (177-207) mg/dL vs. 166 (155-177) mg/dL, 148 (138-159) mg/dL, and 136 (127-144) mg/dL, respectively]. Despite greater insulin resistance, mean HOMA-β was not significantly higher in the PreDM-deficient subgroup than in the PreDM-sufficient, NFG-deficient, and NFG-sufficient subgroups [98 (85-112) vs. 91 (82-101), 123 (112-136), and 115 (106-124), respectively].

CONCLUSION

Subjects with PreDM and low circulating 25(OH)D concentrations are the subgroup of nondiabetic individuals who are the most insulin resistant and have impaired β-cell function, attributes that put them at enhanced risk of T2DM.

Relative Effects of Insulin Resistance and Protease Inhibitor Treatment on Lipid and Lipoprotein Metabolism in HIV-Infected Patients

BACKGROUND

The relationship between insulin resistance, dyslipidemia, HIV infection, and antiretroviral therapy remains unclear, and the atherogenic nature of lipid and lipoprotein profiles in HIV-infected patients has not been fully characterized.

METHOD

We measured plasma lipid and lipoprotein subfractions using Vertical Auto Profile-II methodology and directly measured insulin-mediated glucose disposal in 45 protease inhibitor (PI)-treated and non-PI-treated HIV-infected patients.

RESULTS

PI-treated patients had higher total, LDL, and narrow-density LDL cholesterol (p <.05) and a trend toward higher triglycerides, whereas HDL cholesterol and LDL particle characteristics were unrelated to PI use or history of lipodystrophy. Insulin sensitivity did not differ on the basis of PI therapy, but decreased insulin sensitivity was associated with lower HDL and HDL-3 cholesterol (p <.01); elevated triglyceride (p <.01), VLDL 1+2, and VLDL 3a+3b lipoproteins (p <.01); and smaller, denser (more atherogenic) LDL particle characteristics (p <.01). Thus, the lipoprotein abnormality associated with PI use was increased LDL cholesterol, whereas changes in TG and HDL metabolism were associated with insulin resistance, independent of PI use.

CONCLUSION

The variables of PI-treatment, dyslipidemia, lipodsytrophy, and insulin resistance do not always cluster together in HIV-infected patients, which suggests that the metabolic phenotype emerging in treated patients results from a complex interplay of drug effects, immune restoration, and baseline insulin sensitivity.

Relationship among 25-hydroxyvitamin D concentrations, insulin action, and cardiovascular disease risk in patients with essential hypertension

BACKGROUND

Although low plasma 25-hydroxyvitamin D (25(OH)D) concentrations have been shown to predict risk of hypertension and associated cardiovascular disease (CVD), vitamin D repletion has not consistently lowered blood pressure or decreased CVD. One possibility for this discrepancy is the presence of considerable metabolic heterogeneity in patients with hypertension. To evaluate this possibility, we quantified relationships among insulin resistance, 25(OH)D concentration, and CVD risk factor profile in patients with essential hypertension.

METHODS

Measurements were made of 25(OH)D concentrations, multiple CVD risk factors, and insulin resistance by the steady-state plasma glucose concentration during the insulin suppression test in 140 otherwise healthy patients with essential hypertension.

RESULTS

As a group, the patients were overweight/obese and insulin resistant and had low 25(OH)D concentrations. The more insulin resistant the patients were, the worse the CVD risk profile was. In addition, the most insulin-resistant quartile had significantly lower 25(OH)D concentrations than the most insulin-sensitive quartile (20.3±1.4 vs. 25.8±1.4ng/ml; P = 0.005). In the entire group, 25(OH)D concentration significantly correlated with magnitude of insulin resistance (steady-state plasma glucose concentration; r = -0.20; P = 0.02).

CONCLUSIONS

There was considerable metabolic heterogeneity and substantial difference in magnitude of conventional CVD risk factors in patients with similar degrees of blood pressure elevation. The most insulin-resistant quartile of subjects had the lowest 25(OH)D concentration and the most adverse CVD risk profile, and they may be the subset of patients with essential hypertension most likely to benefit from vitamin D repletion.

Effect of liraglutide administration and a calorie-restricted diet on lipoprotein profile in overweight/obese persons with prediabetes

BACKGROUND AND AIMS

To evaluate the effects of 14 weeks of liraglutide plus modest caloric restriction on lipid/lipoprotein metabolism in overweight/obese persons with prediabetes.

METHODS AND RESULTS

Volunteers with prediabetes followed a calorie-restricted diet (-500 Kcal/day) plus liraglutide (n = 23) or placebo (n = 27) for 14 weeks. The groups were similar in age (58 ± 7 vs. 58 ± 8 years) and body mass index (31.9 ± 2.8 vs. 31.9 ± 3.5 kg/m(2)). A comprehensive lipid/lipoprotein profile was obtained before and after intervention using vertical auto profile (VAP). Weight loss was greater in the liraglutide group than in the placebo group (6.9 vs. 3.3 kg, p < 0.001), as was the fall in fasting plasma glucose concentration (9.9 mg/dL vs. 0.3 mg/dL, p < 0.001). VAP analysis revealed multiple improvements in lipid/lipoprotein metabolism in liraglutide-treated compared with placebo-treated volunteers, including decreases in concentrations of total cholesterol, low-density lipoprotein cholesterol and several of its subclasses, triglyceride, and non-high-density cholesterol. The liraglutide-treated group also had a significant shift away from small, dense low-density lipoprotein-particles, as well as decreases in apolipoprotein B concentration and ratio of apolipoprotein B/apolipoprotein A-1. There were no significant changes in the lipoprotein profile in the placebo-treated group.

CONCLUSION

Treatment with liraglutide plus modest calorie restriction led to enhanced weight loss, a decrease in fasting plasma glucose concentration, and improvement in multiple aspects of lipid/lipoprotein metabolism associated with increased cardiovascular disease (CVD) risk. The significant clinical benefit associated with liraglutide-assisted weight loss in a group at high risk for CVD - obese/overweight individuals with prediabetes - as seen in our pilot study, suggests that this approach deserves further study.

Do differences in waist circumference modify the relationships among body mass index, insulin resistance, and related cardiometabolic risk factors in apparently healthy women?

OBJECTIVE

The aims of the study were to (1) compare the cardiometabolic risk profile between insulin-resistant and non-insulin-resistant women within similar body mass indexes (BMIs) and waist circumference (WC) groupings and (2) test the hypothesis that measurements of BMI are not inferior to WC in identifying insulin resistance.

METHODS

The sample consisted of 899 women without known cardiovascular disease or diabetes. BMI was used to divide participants in normal (<25.0 kg/m(2)), overweight (≥25-29.9 kg/m(2)), and obese (≥30.0 kg/m(2)) subgroups, and waist circumference ≥88 cm was used to identify women with or without abdominal obesity. The 25% of the population with highest fasting insulin concentrations was classified as insulin resistant. BMI, WC, blood pressure, and fasting plasma glucose, insulin, triglyceride, and high-density lipoprotein cholesterol concentrations were compared using analysis of covariance (ANCOVA). The relationships between obesity and insulin resistance were analyzed using univariate, multivariate, and logistic regression.

RESULTS

Triglyceride and glucose concentrations were higher and high-density lipoprotein cholesterol concentrations lower in the insulin-resistant group in each BMI category, as was the case when comparing by abdominal obesity. In the univariate analysis, correlations between obesity and the individual cardiometabolic risk factor were significant but weak. In multivariate analysis including both indices, only body mass independently predicted insulin resistance.

CONCLUSION

Insulin-resistant women were at greater cardiometabolic risk, irrespective of adiposity category. Obesity contributed to a modest variability in insulin resistance, and abdominal obesity does not add to the ability of BMI to predict insulin resistance.

Evaluation of fasting plasma insulin concentration as an estimate of insulin action in nondiabetic individuals: comparison with the homeostasis model assessment of insulin resistance (HOMA-IR)

Insulin-mediated glucose disposal varies severalfold in apparently healthy individuals, and approximately one-third of the most insulin resistant of these individuals is at increased risk to develop various adverse clinical syndromes. Since direct measurements of insulin sensitivity are not practical in a clinical setting, several surrogate estimates of insulin action have been proposed, including fasting plasma insulin (FPI) concentration and the homeostasis model assessment of insulin resistance (HOMA-IR) calculated by a formula employing fasting plasma glucose (FPG) and FPI concentrations. The objective of this study was to compare FPI as an estimate of insulin-mediated glucose disposal with values generated by HOMA-IR in 758 apparently healthy nondiabetic individuals. Measurements were made of FPG, FPI, triglyceride (TG), and high-density lipoprotein cholesterol (HDL-C) concentrations, and insulin-mediated glucose uptake was quantified by determining steady-state plasma glucose (SSPG) concentration during the insulin suppression test. FPI and HOMA-IR were highly correlated (r = 0.98, P < 0.001). The SSPG concentration also correlated to a similar degree (P < 0.001) with FPI (r = 0.60) and HOMA-IR (r = 0.64). Furthermore, the relationship between FPI and TG (r = 0.35) and HDL-C (r = -0.40) was comparable to that between HOMA-IR and TG (r = 0.39) and HDL-C (r = -0.41). In conclusion, FPI and HOMA-IR are highly correlated in nondiabetic individuals, with each estimate accounting for ~40% of the variability (variance) in a direct measure of insulin-mediated glucose disposal. Calculation of HOMA-IR does not provide a better surrogate estimate of insulin action, or of its associated dyslipidemia, than measurement of FPI.

Is measurement of non-HDL cholesterol an effective way to identify the metabolic syndrome?

BACKGROUND AND AIMS

The metabolic syndrome (MetS) has been shown to predict coronary heart disease (CHD). Non-high-density lipoprotein cholesterol (non-HDL-C) is also known to predict CHD, and recent evidence indicated non-HDL-C was able to predict MetS in adolescents. The study aim was to determine whether non-HDL-C serves as a useful metabolic marker for MetS in adults.

METHODS AND RESULTS

Fasting non-HDL-C measurements were obtained in 366 non-diabetic adults not on lipid-lowering therapy. In addition to traditional non-HDL-C cut-points based on Adult Treatment Panel III guidelines, receiver-operating characteristic curve analysis was used to identify an optimal cut-point for predicting MetS. A secondary goal was to assess the relationship between non-HDL-C and insulin resistance, defined as the upper tertile of steady-state plasma glucose concentrations measured during the insulin suppression test. Prevalence of MetS was 40% among participants. Those with MetS had higher mean non-HDL-C (4.17 ± 1.0 vs 3.70 ± 0.85 mmol/L, p < 0.001), and the upper vs lower tertile of non-HDL-C concentrations was associated with 1.8-fold increased odds of MetS (p < 0.05). Traditional non-HDL-C cut-points ≥ 4.14 and ≥ 4.92 mmol/L demonstrated respective sensitivities 46% and 24% (specificities 72% and 89%) for identifying MetS. The optimal non-HDL-C cut-point ≥ 4.45 mmol/L had sensitivity 39% (specificity 82%). Comparable results were observed when non-HDL-C was used to identify insulin resistance.

CONCLUSION

While MetS was associated with increased non-HDL-C, an effective non-HDL-C threshold to predict MetS in adults was not identified. Dyslipidemic nuances may explain why non-HDL-C may be less useful as a metabolic marker for MetS and/or insulin resistance than for CHD.

Habitual shortened sleep and insulin resistance: an independent relationship in obese individuals

OBJECTIVE

Short sleep duration has been reported to be associated with obesity, type 2 diabetes, and pre-diabetes. Since excess weight, glucose abnormalities, and insulin resistance tend to cluster, the individual role insulin resistance may have in habitual shortened sleep is unclear. The study purpose was to assess whether habitual sleep curtailment is independently related to insulin resistance in obese individuals.

MATERIALS/METHODS

Non-diabetic, overweight/obese individuals from the community were stratified as insulin-resistant (n=35) or insulin-sensitive (n=21) based on steady-state plasma glucose concentrations (SSPG) during the insulin suppression test. Seventy-five gram oral glucose tolerance tests were performed. Participants were asked, "On average, how many hours of sleep do you get per night?" Shortened sleep duration was defined as less than 7h of sleep per night.

RESULTS

SSPG concentrations differed 2.5-fold (P<0.001) between insulin-resistant and insulin-sensitive individuals. Impaired fasting glucose and glucose intolerance were prevalent in both groups (>40%); however, body mass index, waist circumference, mean fasting or 2-h post-glucola glucose concentrations were not significantly different. Insulin-resistant individuals reported (mean±SD) fewer hours of sleep than did insulin-sensitive individuals (6.53±1.1 vs. 7.24±0.9 h, P<0.05). Shortened sleep duration was more prevalent among insulin-resistant as compared with insulin-sensitive individuals (60% vs. 24%, P<0.05).

CONCLUSIONS

Non-diabetic, insulin-resistant individuals averaged fewer hours of sleep and were more likely to report shortened sleep duration as compared with similarly obese insulin-sensitive individuals. There appears to be an independent association between habitual shortened sleep and insulin resistance among obese, dysglycemic adults without diabetes.

Adiposity and cardiovascular risk clustering in South Asians

BACKGROUND

South Asians have increased risk for type-2 diabetes and cardiovascular disease, but the relationship between metabolic health and weight has not been described. This study establishes the prevalence of metabolic abnormalities in normal weight, overweight, and obese South Asians.

METHODS

Participants were categorized by body mass index and waist circumference. Subjects with two or more cardiometabolic risk factors (blood pressure, glucose, insulin, triglycerides, high-density lipoprotein cholesterol, and C-reactive protein) were defined as metabolically abnormal.

RESULTS

Forty-one percent of the sample (n=1015) was metabolically abnormal, and 12% of those were normal weight. Of metabolically healthy individuals, 58% were overweight or obese. At a normal level of adiposity, women were more likely to be metabolically unhealthy, whereas men were more likely to be unhealthy with increasing adiposity.

CONCLUSIONS

Similar to other ethnic groups, a significant number of normal weight South Asians can be metabolically unhealthy.

Beyond fasting plasma glucose: the association between coronary heart disease risk and postprandial glucose, postprandial insulin and insulin resistance in healthy, nondiabetic adults

OBJECTIVE

Prediabetes is defined by elevations of plasma glucose concentration, and is aimed at identifying individuals at increased risk of type 2 diabetes and coronary heart disease (CHD). However, since these individuals are also insulin resistant and hyperinsulinemic, we evaluated the association between several facets of carbohydrate metabolism and CHD risk profile in apparently healthy, nondiabetic individuals.

METHODS

Plasma glucose and insulin concentrations were measured before and at hourly intervals for eight hours after two test meals in 281 nondiabetic individuals. Insulin action was quantified by determining the steady-state plasma glucose (SSPG) concentration during the insulin suppression test. CHD risk was assessed by measurements of blood pressure and fasting lipoprotein profile.

RESULTS

For purposes of analysis, the population was divided into tertiles, and the results demonstrated that the greater the 1) fasting plasma glucose (FPG) concentration, 2) incremental plasma insulin response to meals, and 3) SSPG concentration, the more adverse the CHD risk profile (p<0.05). In contrast, the CHD risk profile did not significantly worsen with increases in the incremental plasma glucose response to meals.

CONCLUSIONS

In nondiabetic individuals, higher FPG concentrations, accentuated daylong incremental insulin responses to meals, and greater degrees of insulin resistance are each associated with worse CHD risk profile (higher blood pressures, higher triglycerides, and lower high density lipoprotein cholesterol concentrations). Interventional efforts aimed at decreasing CHD in such individuals should take these abnormalities into consideration.

Cardiometabolic risk factors and obesity: does it matter whether BMI or waist circumference is the index of obesity?

BACKGROUND

It has been suggested that the cardiometabolic risk associated with excess adiposity is particularly related to central obesity.

OBJECTIVE

The objective was to compare the associations between cardiometabolic risk of apparently healthy individuals and measures of central obesity [waist circumference (WC)] and overall obesity [body mass index (BMI)].

DESIGN

In this cross-sectional, observational study, 492 subjects (306 women and 303 non-Hispanic whites) were classified by BMI (in kg/m²) as normal weight (BMI <25) or overweight/obese (BMI = 25.0-34.9) and as having an abnormal WC (≥80 cm in women and ≥94 cm in men) or a normal WC (<80 cm in women and <94 cm in men). Measurements were also made of the cardiometabolic risk factors age, systolic blood pressure (SBP), and fasting plasma glucose (FPG), triglyceride, and high-density lipoprotein (HDL)-cholesterol concentrations. Associations among cardiometabolic risk factors and BMI and WC were evaluated with Pearson correlations.

RESULTS

There was a considerable overlap in the normal and abnormal categories of BMI and WC, and ~81% of the subjects had both an abnormal BMI and WC. In women, BMI and WC correlated with SBP (r = 0.30 and 0.19, respectively), FPG (r = 0.25 and 0.22, respectively), triglycerides (r = 0.17 and 0.20, respectively), and HDL cholesterol (r = -0.23 and -0.20, respectively) (P < 0.01 for all). In men, BMI and WC also correlated with SBP (r = 0.22 and 0.22, respectively), FPG (r = 0.22 and 0.25, respectively), triglycerides (r = 0.21 and 0.18, respectively), and HDL cholesterol (r = -0.20 and -0.13, respectively) [P < 0.05 for all, except for the association of WC with HDL cholesterol (P = 0.08)].

CONCLUSIONS

Most individuals with an abnormal BMI also have an abnormal WC. Both indexes of excess adiposity are positively associated with SBP, FPG, and triglycerides and inversely associated with HDL cholesterol.

Plasma triglyceride/HDL-cholesterol ratio, insulin resistance, and cardiometabolic risk in young adults

Studies in mature adults suggest that the plasma concentration ratio of triglyceride (TG)/HDL-cholesterol (HDL-C) provides a simple way to identify apparently healthy individuals who are insulin resistant (IR) and at increased cardiometabolic risk. This study extends these observations by examining the clinical utility of the TG/HDL-C ratio and the metabolic syndrome (MetS) in 2,244 healthy college students (17-24 years old) of Mexican Mestizo ancestry. The TG/HDL-C ratio separating the 25% with the highest value was used to identify IR and increased cardiometabolic risk. Cardiometabolic risk factors were more adverse in men and women whose TG/HDL-C ratios exceeded 3.5 and 2.5, respectively, and approximately one third were identified as being IR. The MetS identified fewer individuals as being IR, but their risk profile was accentuated. In conclusion, both a higher TG/HDL-C ratio and a diagnosis of the MetS identify young IR individuals with an increased cardiometabolic risk profile. The TG/HDL-C ratio identified a somewhat greater number of "high risk" subjects, whereas the MetS found a group whose risk profile was somewhat magnified. These findings suggest that the TG/HDL-C ratio may serve as a simple and clinically useful approach to identify apparently healthy, young individuals who are IR and at increased cardiometabolic risk.

Comparison of the abilities of the plasma triglyceride/high-density lipoprotein cholesterol ratio and the metabolic syndrome to identify insulin resistance

This study compares the ability of an elevated triglyceride/high-density lipoprotein cholesterol (TG/HDL-C) ratio, using sex-specific cut-points, to identify insulin-resistant individuals within a population without known cardiac disease or diabetes with that obtained using the diagnostic criteria of the metabolic syndrome (MetS). Measurements were made of waist circumference (WC), systolic and diastolic blood pressure, fasting plasma glucose, fasting plasma insulin (FPI), plasma TG and plasma HDL-C concentrations in 1102 women and 464 men. These data were used to classify subjects as being insulin resistant (FPI concentration in the upper quartile) and having the MetS or an elevated TG/HDL-C ratio (>2.5 and >3.5 for women and men, respectively). The sensitivity and specificity with which the two indices identified insulin-resistant subjects were similar (43% and 81% for TG/HDL-C ratio and 45% and 82% for MetS), as the number of individuals was found with either an elevated TG/HDL-C ratio (n = 386) or the MetS (n = 384). Eighty-one per cent of the individuals were identified concordantly. Cardio-metabolic risk profiles in 'low-risk' individuals identified by a low TG/HDL-C ratio were comparable to those who did not have the MetS, and this was also the case when comparing 'high-risk' groups identified by having the MetS or an elevated TG/HDL-C ratio. These findings suggest that TG/HDL-C concentration ratio is as adequate as MetS diagnosis to identify insulin-resistant subjects.

Identifying cardiovascular disease risk and outcome: use of the plasma triglyceride/high-density lipoprotein cholesterol concentration ratio versus metabolic syndrome criteria

BACKGROUND

Metabolic syndrome (MetS) has been shown to predict both risk and CVD events. We have identified sex-specific values for the triglyceride/high-density lipoprotein cholesterol (TG/HDL-C) ratio associated with an unfavourable cardio-metabolic risk profile, but it is not known whether it also predicts CVD outcome.

METHODS

To quantify risk for CVD outcomes associated with a high TG/HDL-C ratio and to compare this risk with that predicted using MetS, a population longitudinal prospective observational study was performed in Rauch City, Buenos Aires, Argentina. In 2003 surveys were performed on a population random sample of 926 inhabitants. In 2012, 527 women and 269 men were surveyed again in search of new CVD events. The first CVD event was the primary endpoint. Relative risks for CVD events between individuals above and below the TG/HDL-C cut-points, and with or without MetS, were estimated using Cox proportional hazard.

MAIN OUTCOME

The first CVD event was the primary endpoint. Relative risks for CVD events between individuals above and below the TG/HDL-C cut-points, and with or without MetS, were estimated using Cox proportional hazard.

RESULTS

The number of subjects deemed at 'high' CVD risk on the basis of an elevated TG/HDL-C ratio (30%) or having the MetS (35%) was relatively comparable. The unadjusted hazard risk was significantly increased when comparing 'high' versus 'low' risk groups no matter which criteria was used, although it was somewhat higher in those with the MetS (HR = 3.17, 95% CI:1.79-5.60 vs. 2.16, 95% CI:1.24-3.75). However, this difference essentially disappeared when adjusted for sex and age (HR = 2.09, 95% CI:1.18-3.72 vs. 2.01, 95% CI:1.14-3.50 for MetS and TG/HDL-C respectively).

CONCLUSIONS

An elevated TG/HDL-C ratio appears to be just as effective as the MetS diagnosis in predicting the development of CVD.

Measurement of insulin-mediated glucose uptake: direct comparison of the modified insulin suppression test and the euglycemic, hyperinsulinemic clamp

BACKGROUND

Two direct measurements of peripheral insulin sensitivity are the M value derived from the euglycemic, hyperinsulinemic clamp (EC) and the steady-state plasma glucose (SSPG) concentration derived from the insulin suppression test (IST). Prior work suggests that these measures are highly correlated, but the agreement between them is unknown. To determine the agreement between SSPG and M and to develop transformation equations to convert SSPG to M and vice versa, we directly compared these two measurements in the same individuals.

METHODS

A total of 15 nondiabetic subjects (9 women and 6 men) underwent both an EC and a modified version of the IST within a median interval of 5days. We performed standard correlation metrics of the two measures and developed transformation regression equations for the two measures.

RESULTS

The mean±SD age of the subjects was 57±7years and body mass index, 27.7±3.9kg/m(2). The median (interquartile range) SSPG concentration was 6.7 (5.1, 9.8) mmol/L and M value, 49.6 (28.9, 64.2) μmol/min/kg-LBM. There was a highly significant correlation between SSPG and M (r=-0.87, P <0.001). The relationship was best fit by regression models with exponential/logarithmic functions (R(2)=0.85). Bland-Altman plots demonstrated an excellent agreement between these measures of insulin action.

CONCLUSION

The SSPG and M are highly related measures of insulin sensitivity and the results provide the means to directly compare the two measurements.

Body mass index and waist circumference associate to a comparable degree with insulin resistance and related metabolic abnormalities in South Asian women and men

AIM

The aim of this study was to test the hypothesis that body mass index (BMI) and waist circumference (WC) associate to a comparable degree with insulin resistance and cardiometabolic risk factors in South Asians.

METHODS

We measured blood pressure and fasting glucose, insulin, triglyceride, high-density lipoprotein cholesterol (HDL-C), high-sensitivity C-reactive protein (hs-CRP), and fibrinogen and calculated the homeostasis model assessment of insulin resistance (HOMA-IR) in a community-based sample of 923 nondiabetic South Asians.

RESULTS

BMI and WC were highly correlated in both genders (r = 0.82 and 0.87). The relationship between BMI and values of blood pressure, glucose, insulin, HOMA-IR, triglyceride, HDL-C, hs-CRP, and fibrinogen was comparable to that between WC and these variables. Fasting insulin and HOMA-IR correlated most strongly with BMI (r = 0.49 to 0.56) and WC (r = 0.52 to 0.59).

CONCLUSION

These results show that BMI and WC associate to a comparable degree with estimates of insulin resistance and related metabolic abnormalities in South Asians.

Relation among the plasma triglyceride/high-density lipoprotein cholesterol concentration ratio, insulin resistance, and associated cardio-metabolic risk factors in men and women

Results of recent studies using the ratio of plasma triglyceride (TG) to high-density lipoprotein (HDL) cholesterol concentration to identify insulin-resistant patients at increased cardiometabolic risk have emphasized that the cut point used for this purpose will vary with race. Because TG and HDL cholesterol concentrations vary with gender, this analysis was initiated to define gender-specific plasma TG/HDL cholesterol concentration ratios that best identified high-risk subjects among women (n = 1,102) and men (n = 464) of primarily European ancestry. Insulin resistance was defined as the 25% of the population with the highest values for fasting plasma insulin concentration and homeostasis model assessment of insulin resistance. Using TG/HDL concentration ratios >2.5 in women and >3.5 in men identified subgroups of men and women that were comparable in terms of insulin resistance and associated cardiometabolic risk, with significantly higher values for fasting plasma insulin, homeostasis model assessment of insulin resistance, blood pressure, body mass index, waist circumference, and glucose and TG concentrations and lower HDL cholesterol concentrations than in women and men below these cut points. The sensitivity and specificity of these gender-specific cut points to identify insulin-resistant subjects were about 40% and about 80%, respectively. In conclusion, the plasma TG/HDL cholesterol concentration ratio that identifies patients who are insulin resistant and at significantly greater cardiometabolic risk varies between men and women.

Relations between obesity, insulin resistance, and 25-hydroxyvitamin D

BACKGROUND

Although low circulating 25-hydroxyvitamin D [25(OH)D] concentrations have been associated with insulin resistance and obesity, the relations between these 3 variables have not been completely resolved.

OBJECTIVE

The objective was to compare circulating 25(OH)D concentrations in apparently healthy individuals who were matched for degree of obesity or insulin sensitivity.

DESIGN

This was a case-control study in which 78 apparently healthy individuals were classified as being normal weight (NW) or obese (OB) on the basis of their BMI and as being insulin sensitive (IS) or insulin resistant (IR) on the basis of their steady state plasma glucose (SSPG) concentration during the insulin suppression test.

RESULTS

Groups did not differ in terms of age, sex distribution, race, or mean (± SD) plasma 25(OH)D concentration. Values for 25(OH)D were 32 ± 10, 30 ± 10, and 28 ± 8 ng/mL in NW-IS, OB-IS, and OB-IR groups, respectively. These concentrations were essentially identical when comparing IR with IS subjects matched for BMI or when comparing OB with NW subjects matched for SSPG. Concentrations of 25(OH)D ≤ 30 ng/mL were somewhat more common in OB subjects than in NW subjects (54% compared with 35%), but SSPG concentrations were not different within either the IR or IS groups when subgroups with 25(OH)D concentrations ≤ 30 or > 30 ng/mL were compared.

CONCLUSIONS

In 78 individuals, 47% of whom were vitamin D deficient or insufficient (≤ 30 ng/mL), 25(OH)D concentrations did not vary with differences in insulin sensitivity (SSPG concentration) when matched for BMI (OB-IR compared with OB-IS). Similarly, when matched for SSPG concentrations, plasma 25(OH)D concentrations were not different in NW or OB individuals (NW-IS compared with OB-IS).

Comparison of two methods using plasma triglyceride concentration as a surrogate estimate of insulin action in nondiabetic subjects: triglycerides × glucose versus triglyceride/high-density lipoprotein cholesterol

The objective was to compare relationships between insulin-mediated glucose uptake and surrogate estimates of insulin action, particularly those using fasting triglyceride (TG) and high-density lipoprotein cholesterol (HDL-C) concentrations. Insulin-mediated glucose uptake was quantified by determining the steady-state plasma glucose (SSPG) concentration during the insulin suppression test in 455 nondiabetic subjects. Fasting TG, HDL-C, glucose, and insulin concentrations were measured; and calculations were made of the following: (1) plasma concentration ratio of TG/HDL-C, (2) TG × fasting glucose (TyG index), (3) homeostasis model assessment of insulin resistance, and (4) insulin area under the curve (insulin-AUC) during a glucose tolerance test. Insulin-AUC correlated most closely with SSPG (r ∼ 0.75, P < .001), with lesser but comparable correlations between SSPG and TG/HDL-C ratio, TyG index, homeostasis model assessment of insulin resistance, and fasting TG and insulin (r ∼ 0.60, P < .001). Calculations of TG/HDL-C ratio and TyG index correlated with SSPG concentration to a similar degree, and the relationships were comparable to estimates using fasting insulin. The strongest relationship was between SSPG and insulin-AUC.

Insulin resistance: the link between obesity and cardiovascular disease

There seems to be general agreement that the prevalence of obesity is increasing in the United States and that we are in the midst of an obesity epidemic. The disease-related implications of this epidemic have received an enormous amount of publicity in the popular media, but public awareness of the untoward effects of excess weight has not led to an effective approach to dealing with the dilemma. The gravity of the problem is accentuated in light of the report that only approximately 50% of physicians polled provided weight loss counseling. Given the importance of excess adiposity as increasing the risk of CVD, 2DM, and hypertension and the combination of an increase in the prevalence of overweight/obesity and a health care system unprepared to deal with this situation, it is essential that considerable thought be given as to how to best address this dilemma. In this context, it must be emphasized that CVD, 2DM, and hypertension are characterized by resistance to insulin-mediated glucose disposal and that insulin resistance and the compensatory hyperinsulinemia associated with insulin resistance have been shown to be independent predictors of all three clinical syndromes. It has also been apparent for many years that overweight/obese individuals tend to be insulin resistant and become more insulin sensitive with weight loss.25 In light of these observations, it seems reasonable to suggest that insulin resistance is the link between overweight/obesity and the adverse clinical syndromes related to excess adiposity. The evidence summarized in this review shows that the more overweight an individual, the more likely he or she is insulin resistant and at increased risk to develop all the abnormalities associated with this defect in insulin action. Not all overweight/obese individuals are insulin resistant, however, any more than all insulin resistant individuals are overweight/obese. More important, there is compelling evidence that CVD risk factors are present to a significantly greater degree in the subset of overweight/obese individuals that is also insulin resistant. Not surprisingly,we have also demonstrated that an improvement in CVD risk factors with weight loss occurs to a significantly greater degree in those overweight/obese individuals who are also insulin resistant at baseline. In view of the ineffectiveness of current clinical approaches to weight loss, it seems necessary to recognize that not all overweight/obese individuals are at equal risk to develop CVD and that it is clinically useful to identify those at highest risk. The simplest way to achieve this task seems to be focusing on the CVD risk factors that are highly associated with insulin resistance/hyperinsulinemia. If this is done, then intense efforts at weight control can be brought to bear on those who not only need it the most but also have the most to gain by losing weight.

Relationships among insulin resistance, type 2 diabetes, essential hypertension, and cardiovascular disease: similarities and differences

Insulin resistance plays a major role in the pathogenesis and clinical course of patients with type 2 diabetes (2DM) and essential hypertension. However, the syndromes differ in prevalence of insulin resistance, and associated insulin secretory response. Essentially all patients with type 2 diabetes are insulin resistant, whereas only approximately 50% of those with essential hypertension are insulin resistant. Furthermore, 2DM develops when the pancreatic β-cell can no longer maintain the degree of compensatory hyperinsulinemia needed to prevent hyperglycemia. In contrast, the compensatory hyperinsulinemia that prevents most insulin resistant individuals from developing 2DM acts on normally insulin sensitive tissues in a manner that predisposes to the development of essential hypertension. This review will discuss these similarities and differences in some detail, as well as exploring the relationship among insulin resistance and related metabolic abnormalities in the pathogenesis of cardiovascular disease in patients with 2DM and essential hypertension.