Insulin secretion and insulin sensitivity on the oral glucose tolerance test (OGTT) in middle-aged Japanese

Intravoxel incoherent motion diffusion-weighted imaging of pancreas: Probing evidence of β-cell dysfunction in asymptomatic adults with hyperglycemia in vivo

PURPOSE

Early evaluation of β-cell dysfunction of hyperglycemic patients in asymptomatic adults would be valuable for timely prevention of the diabetes. This study aimed to evaluate functional changes in the pancreas using intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) and determine whether it could be used as a non-invasive method of assessing β-cell dysfunction.

METHODS

This prospective cohort study was conducted from August 2022 to November 2022 in Jinan University Affiliated Guangdong Second General Hospital. Three groups were enrolled and underwent IVIM-DWI: confirmed patients with type 2 diabetes (T2DM); hyperglycemic patients in asymptomatic adults; and the volunteers with normal glucose tolerance (NGT). Imaging parameters were obtained: apparent diffusion coefficient (ADC), the true diffusion coefficient (Dt), the pseudo-diffusion coefficient (Dp), and the perfusion fraction (f). The β-cell function indexes were calculated from blood examinations: composite insulin sensitivity index (ISI), 60-min insulinogenic index (IGI60), and the disposition index (DI). We compared imaging parameters among three groups, calculated the diagnostic performance of them for differentiating different groups, and the reproducibility of them was evaluated using intraclass correlation coefficient (ICC).

RESULTS

The imaging parameters except f gradually decreased among the groups with significant differences for ADC (p < 0.0001), Dt (p < 0.0001), and Dp (p = 0.013). Dt demonstrated the best diagnostic performance for differentiating asymptomatic patients from NGT (Area Under Curve [AUC] = 0.815, p < 0.0001). IVIM-DWI parameters correlated with composite ISI and DI, of which, Dt has the highest correlation with DI (Pearson correlation coefficient [r] = 0.546, p < 0.0001). The ICC of IVIM-DWI parameters was very good, Dt was highest (Interobserver ICC = 0.938, 95% Confidence Interval [CI], 0.899-0.963; Intraobserver ICC = 0.941, 95% CI, 0.904-0.965).

CONCLUSION

IVIM-DWI is a non-invasive quantitative method that can identify β-cell dysfunction in the pancreas.

Body Roundness Index Is Better Correlated with Insulin Sensitivity than Body Shape Index in Young and Middle-Aged Japanese Persons

Aims: The present study aimed to clarify the relationships between novel and traditional anthropometric indices and insulin sensitivity (SI) in young and middle-aged Japanese persons with normal glucose tolerance (NGT), and middle-aged Japanese persons with NGT and glucose intolerance. Methods: Plasma glucose and insulin levels were measured in 1270 young (age <40 years) and 2153 middle-aged persons with NGT (n = 1531) and glucose intolerance (n = 622) during a 75-g oral glucose tolerance test. Height (Ht), weight, and waist circumference (WC) were measured. The body mass index (BMI), WC, and the WC/Ht ratio were used as traditional anthropometric indices. A body shape index (ABSI) and the body roundness index (BRI) were calculated as novel indices. Indices of SI (Matsuda index and 1/homeostasis model assessment of insulin resistance) were calculated and compared with anthropometric indices. Results: The ABSI showed a weak correlation with SI indices in all groups. The BRI showed almost the same correlation with SI indices as the BMI, WC, and WC/Ht in all groups. The inverse correlation between each of the anthropometric indices other than ABSI and SI indices was weak in young persons, at 0.16-0.27 (Spearman's ρ values), but strong in middle-aged persons, at 0.38-1.00. On receiver-operating characteristic (ROC) curve analysis for detection of insulin resistance, the ABSI had a lower area under the ROC curve (AUC) than the other anthropometric indices, and the BRI and the WC/Ht ratio showed similar AUCs. The AUCs for the BRI and WC/Ht ratio were the highest in middle-aged men with NGT and glucose intolerance. Conclusions: The BRI, not the ABSI, was better correlated with SI in young and middle-aged Japanese persons. The BRI and WC/Ht ratio were comparable in their correlations with SI and the detection of insulin resistance in the participants of the present study.

Hepatic Steatosis and High-normal Fasting Glucose as Risk Factors for Incident Prediabetes

Context

The role of hepatic steatosis (HS) in the initial stages of developing type 2 diabetes remains unclear.

Objective

We aimed to clarify the impact of HS indexed by Fatty Liver Index (FLI) and high-normal fasting plasma glucose (FPG) as risk factors for incident prediabetes in a nonobese cohort.

Methods

Data from 1125 participants with ADA-defined normal glucose metabolism (median age 52 years; BMI 23.1 kg/m²) were used for retrospective analysis. In the entire population, correlation between normal FPG and FLI was evaluated by multiple regression adjusted for age and sex. Follow-up data from 599 participants in whom 75-g OGTT was repeated 3.7 years later showed that 169 developed prediabetes. This was analyzed by the multivariate Cox proportional hazards model.

Results

In the entire population, FLI was positively correlated with FPG (P < 0.01): mean FLI increased from 15.8 at FPG 4.2 mmol/L to 31.6 at FPG 5.5 mmol/L. Analysis of the 599 participants (2061 person-years) by Cox model, adjusted for sex, age, family history of diabetes, ISI_MATSUDA, and Stumvoll-1, clarified an increased risk of prediabetes with high-normal FPG and FLI. Risk was increased 2.2 times with FLI ≥ 16.5 vs FLI < 16.5, P < 0.001, and increased 2.1 times in participants with FPG ≥ 5.3 mmol/L, P < 0.001. Cutoff values (unadjusted) were obtained by ROC at the point of the largest Youden’s index using the entire range of the variables.

Conclusion

Even among nonobese individuals, HS indexed by FLI and a high-normal FPG (≥ 5.3 mmol/L) are risk factors for prediabetes, independently from insulin.

Oral fat tolerance testing identifies abnormal pancreatic β-cell function and insulin resistance in individuals with normal glucose tolerance

AIMS/INTRODUCTION

Insulin sensitivity and β-cell function are affected by lipid metabolism disorders, even before the onset of type 2 diabetes. People are in the postprandial state most of the time. Therefore, identifying postprandial hyperlipemia is important. This study aimed to assess patients with abnormalities in lipid metabolism, but with normal glucose tolerance, using oral fat tolerance testing (OFTT) to identify defects in insulin sensitivity and β-cell function.

MATERIALS AND METHODS

We included 248 volunteers with normal glucose tolerance who underwent OFTT. They were divided into three groups in accordance with their fasting and 4-h postprandial triglyceride (TG) concentrations. Their lipid concentrations during OFTT were compared. The disposition index (DI) was applied to estimate β-cell function, and the Matsuda insulin sensitivity index (ISI_M ) was used to assess insulin sensitivity. We used multiple linear regression analysis to estimate the relationships of fasting and postprandial TG concentrations with β-cell function and insulin sensitivity .

RESULTS

The changes in TG concentrations during OFTT were more marked than those in low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol or total cholesterol concentrations. As lipid metabolism deteriorated, the ISI_M and the DI gradually decreased. Multiple linear regression analysis showed that fasting and 4-h postprandial TG concentrations affected LnISI_M and LnDI.

CONCLUSIONS

In individuals with normal glucose tolerance, β-cell function and insulin sensitivity gradually decrease with a deterioration in the lipid profile. Not only fasting TG, but also postprandial TG concentrations are independent risk factors for impaired β-cell function and insulin resistance.

Accuracy of 1-Hour Plasma Glucose During the Oral Glucose Tolerance Test in Diagnosis of Type 2 Diabetes in Adults: A Meta-analysis

OBJECTIVE

One-hour plasma glucose (1-h PG) during the oral glucose tolerance test (OGTT) is an accurate predictor of type 2 diabetes. We performed a meta-analysis to determine the optimum cutoff of 1-h PG for detection of type 2 diabetes using 2-h PG as the gold standard.

RESEARCH DESIGN AND METHODS

We included 15 studies with 35,551 participants from multiple ethnic groups (53.8% Caucasian) and 2,705 newly detected cases of diabetes based on 2-h PG during OGTT. We excluded cases identified only by elevated fasting plasma glucose and/or HbA_1c. We determined the optimal 1-h PG threshold and its accuracy at this cutoff for detection of diabetes (2-h PG ≥11.1 mmol/L) using a mixed linear effects regression model with different weights to sensitivity/specificity (2/3, 1/2, and 1/3).

RESULTS

Three cutoffs of 1-h PG, at 10.6 mmol/L, 11.6 mmol/L, and 12.5 mmol/L, had sensitivities of 0.95, 0.92, and 0.87 and specificities of 0.86, 0.91, and 0.94 at weights 2/3, 1/2, and 1/3, respectively. The cutoff of 11.6 mmol/L (95% CI 10.6, 12.6) had a sensitivity of 0.92 (0.87, 0.95), specificity of 0.91 (0.88, 0.93), area under the curve 0.939 (95% confidence region for sensitivity at a given specificity: 0.904, 0.946), and a positive predictive value of 45%.

CONCLUSIONS

The 1-h PG of ≥11.6 mmol/L during OGTT has a good sensitivity and specificity for detecting type 2 diabetes. Prescreening with a diabetes-specific risk calculator to identify high-risk individuals is suggested to decrease the proportion of false-positive cases. Studies including other ethnic groups and assessing complication risk are warranted.

Clinical Characteristics and Associated Risk Factors of Prediabetes in the Southwestern Region of Korea from 2010-2019

This study investigated the clinical characteristics and associated risk factors of prediabetes in the southwestern region of Korea. A total of 323 subjects from 13 prediabetes studies were included in the data analysis. Subjects with prediabetes were divided into the following subtypes: (1) normal glucose tolerance (NGT) with HbA1c 5.7%–6.4%; (2) isolated impaired fasting glucose (I-IFG); (3) isolated impaired glucose tolerance (I-IGT); and (4) combined I-IFG and I-IGT (C-IFG/IGT). Clinical and biochemical variables were compared among subtypes, and multivariate logistic regression analysis was used to identify risk factors for prediabetes subtypes. The overall proportion of subjects with NGT, I-IFG, I-IGT and C-IFG/IGT was 8.4%, 20.7%, 33.1% and 37.8%, respectively. In men, C-IFG/IGT was the most common subtype, while in women, I-IGT was the most common. The parameters related to dysglycemia, atherosclerosis and liver dysfunction were higher in subjects in the C-IFG/IGT subtype than in other subtypes. Multiple linear regression analysis revealed independent risk factors for increased FPG, 2h-PPG and HbA1c levels. This study identified the clinical features and independent risk factors for prediabetes subtypes.

Prolonged plasma glucose elevation on oral glucose tolerance test in young healthy Japanese individuals

AIMS

This study aims to assess insulin secretion and resistance through oral glucose tolerance test (OGTT) among young Japanese individuals.

SUBJECTS AND METHODS

We enrolled 595 young healthy Japanese individuals aged 22-29 years. They underwent an OGTT, and their results were divided into 4 groups (I-IV), according to the time at which their plasma glucose concentration declined below the fasting glucose concentration (30, 60 or 120 minutes or never as groups I, II, III and IV, respectively).

RESULTS

We classified 575 normal glucose-tolerant subjects into 4 groups (I-IV) with I: 28 (4.9%), II: 120 (20.9%), III: 143 (24.9%) and IV: 284 (49.4%) individuals. The Matsuda, insulinogenic and disposition indices were decreased from groups I to IV. ROC curves of disposition index reflecting the composition of insulin secretion and sensitivity classified the prolonged glucose elevation group (group III + IV) from the rapid glucose lowering group (group II; AUC = 0.847).

CONCLUSIONS

Even in a young and healthy Japanese individual within the physiological range of glycaemic control, there is a sequential decrease in insulin sensitivity and secretion.

Indirect insulin resistance detection: Current clinical trends and laboratory limitations

There is a steady increase in the number of overweight and obese people worldwide and increasingly, younger people. Excess adipose tissue impairs the action of insulin, leading to insulin resistance (IR). Tissue IR is a major factor in relation to cardiovascular disease, metabolic syndrome and diabetes. Thus, it is important to recognize at the pre-disease stage with the possibility of therapeutic intervention. IR is assessed using indicators of epidemiological significance, most often calculated from fasting and postprandial glucose and insulin values, so-called indirect indicators of insulin resistance. The most commonly used parameter is the Homeostatic Model Assessment (HOMA). Although the Quantitative Insulin Sensitivity Check Index (QUICKI), Matsuda Index and the Insulin Secretion-Sensitivity Index-2 (ISSI-2) are also used, the values of these indices established for IR vary for different age, sex, populations and ethnic groups. Thus, appropriate reference values of indirect indices should be determined for such groups, and when this is precluded, data from published studies carried out on the most ethnically, socio-economically and age-matched populations should be applied.

Impaired β-cell function and decreased insulin sensitivity in subjects with normal oral glucose tolerance but isolated high glycosylated hemoglobin

The pathophysiology is distinct in various state of glucose metabolism abnormalities. As the defect of individuals with normal oral glucose tolerance (NGT) but isolated high glycosylated hemoglobin (HbA1c), i.e. iHH, was ambiguous, we aimed to investigate the insulin sensitivity and β-cell function of iHH. According to the ADA criteria of HbA1c cut-off point (5.7%), 3,517 subjects with NGT screened from a total of 7,855 middle-aged and elderly Chinese without known diabetes were divided into two groups, 1,877 subjects with HbA1c < 5.7% and 1,640 with HbA1c ≥ 5.7% (i.e. iHH). A variety of indexes from blood glucose and insulin levels of oral glucose tolerance were calculated to evaluate insulin sensitivity and β-cell function. Compared with subjects with HbA1c < 5.7%, individuals with iHH had increased homeostasis model assessment of insulin resistance (HOMA-IR), early-phase and total insulin release indexes (insulin release index 30 min and 120 min, i.e. INRS30 and INSR120), and decreased Matsuda insulin sensitivity index (Matsuda ISI) and early-phase disposition index (DI30). After adjustment for confounding factors, the significant difference of HOMA-IR and INSR30 between the two groups vanished, however, Matsuda ISI and DI30 remained significantly lower and INSR120 was still higher in iHH group compared with HbA1c < 5.7%. In conculsion, subjects with NGT may not be perfectly healthy in glycometabolism, those with iHH have impaired early-phase β-cell function and decreased insulin sensitivity.

Insulin Secretion and Risk for Future Diabetes in Subjects with a Nonpositive Insulinogenic Index

AIM

To characterize subjects with a nonpositive insulinogenic index and longitudinally observe changes in their glucose tolerance.

SUBJECTS AND METHODS

A historical cohort study was conducted using data from the medical checkups of public school workers. Indices of insulin secretion and insulin sensitivity derived from oral glucose tolerance test (OGTT) and the incidences of diabetes and impaired glucose tolerance (IGT) were compared among subgroups of subjects with different insulinogenic index (change in insulin/change in glucose over the first 30 min on the OGTT).

RESULTS

Of the 1464 nondiabetic subjects at baseline, 72 (4.9%) subjects had a nonpositive insulinogenic index: 42 of those subjects had a nonpositive glucose response (ΔGlu_0-30 ≤ 0) and 30 had a nonpositive insulin response (ΔIns_0-30 ≤ 0). Compared with subjects who had normal glucose tolerance (NGT) with insulinogenic index ≥ 0.4, subjects with a nonpositive glucose response had a higher first-phase Stumvoll and lower incidences of diabetes and IGT based on a log-rank test (p < 0.05), whereas subjects with a nonpositive insulin response had lower indices of insulin secretion and a higher incidence of diabetes (p < 0.05).

CONCLUSIONS

These results demonstrate that in the first 30 min on the OGTT, subjects with a nonpositive insulinogenic index due to a nonpositive glucose response (ΔGlu_0-30 ≤ 0) had a lower risk for future diabetes and that subjects with nonpositive insulin response (ΔIns_0-30 ≤ 0) had a higher risk for future one.

Associations between Sleep-Disordered Breathing and Metabolic Risk Factors beyond Obesity

OBJECTIVE

Individuals with multiple metabolic risk factors often experience concomitant sleep-disordered breathing (SDB). We aimed to determine the associations of SDB with individual components of metabolic syndrome independent of obesity.

METHODS

A cross-sectional study was conducted in 1137 employees aged 30-64 years. Apnea-hypopnea index (AHI) was assessed using a portable monitor for obstructive sleep apnea by admission. Of these, 451 participants took an oral glucose tolerance test to assess homeostatic model assessment of insulin resistance (HOMA-IR) and Matsuda insulin sensitivity index (ISI).

RESULTS

The odds ratio (OR) of the highest category of the AHI (≥15 episodes per hour) compared to the lowest one (<5 episodes per hour) was significantly elevated for hypertension, for hypertriglyceridemia, and for low HDL-cholesterolemia when adjusted for age, sex, and alcohol and smoking status (p < 0.05). After further adjustment for body mass index (BMI) or waist circumference, the associations for hypertension still remained statistically significant (p < 0.05) while those for hypertriglyceridemia and low HDL-cholesterolemia were no longer significant. The association between higher insulin resistance as assessed by HOMA-IR and Matsuda ISI and higher categories of the AHI was also lost after adjustment for BMI.

CONCLUSION

Obesity was a strong confounding factor in the association between SDB and most metabolic risk factors including insulin resistance, except for hypertension. Further longitudinal study is needed to examine the temporal or causal relationships between SDB and metabolic risk factors. This trial is registered with UMIN-CTR UMIN000028067.

Postchallenge hyperglycemia in subjects with low body weight: implication for small glucose volume

A hypothesis that postchallenge hyperglycemia in subjects with low body weight (BW) may be due, in part, to small glucose volume (G_V) was tested. We studied 11,411 nondiabetic subjects with a mean BW of 63.3 kg; 5,282 of them were followed for a mean of 5.3 yr. In another group of 1,537 nondiabetic subjects, insulin sensitivity, secretion, and a product of the two (index of whole body insulin action) were determined. Corrected 2 h-plasma glucose (2hPG_corr) during a 75-g oral glucose tolerance test in subjects with BW ≤ 59 kg was calculated as 2hPG_corr = δPG_2h · ECW/[16.1 (males) or 15.3 (females)] + fasting PG (FPG), where δPG_2h is plasma glucose increment in 2 h; ECW is extracellular water (surrogate of G_V); FPG is fasting plasma glucose; and 16.1 and 15.3 are ECW of men and women, respectively, with BW = 59 kg. Multivariate analyses for BW with adjustment for age, sex, and percent body fat were undertaken. BW was, across its entire range, positively correlated with FPG (P < 0.01). Whereas BW was correlated with 2hPG and δPG in a skewed J-shape, with inflections at around 60 kg (P for nonlinearity < 0.01 for each). Nonetheless, in those with BW ≤ 59 kg, insulin sensitivity, secretion, and action were unattenuated, and incident diabetes was less compared with heavier counterparts. BW was linearly correlated with 2hPG_corr, i.e., the J-shape correlation was mitigated by the correction. In conclusion, postchallenge hyperglycemia in low BW subjects is in part due to small G_V rather than impaired glucose metabolism.

Predictive models for conversion of prediabetes to diabetes

AIM

To clarify the natural course of prediabetes and develop predictive models for conversion to diabetes.

METHODS

A retrospective longitudinal study of 2105 adults with prediabetes was carried out with a mean observation period of 4.7years. Models were developed using multivariate logistic regression analysis and verified by 10-fold cross-validation. The relationship between [final BMI minus baseline BMI] (δBMI) and incident diabetes was analyzed post hoc by comparing the diabetes conversion rate for low (< -0.31kg/m²) and high δBMI (≥ -0.31kg/m²) subjects after matching the two groups for the covariates.

RESULTS

Diabetes developed in 252 (2.5%/year), and positive family history, male sex, higher systolic blood pressure, plasma glucose (fasting and 1h- and 2h-values during 75g OGTT), hemoglobin A1c (HbA1c) and alanine aminotransferase were significant, independent predictors for the conversion. By using a risk score (RS) that took account of all these variables, incident diabetes was predicted with an area under the ROC curve (95% CI) of 0.80 (0.70-0.87) and a specificity of prediction of 61.8% at 80% sensitivity. On division of the participants into high- (n=248), intermediate- (n=336) and low-risk (n=1521) populations, the conversion rates were 40.1%, 18.5% and 5.9%, respectively. The conversion rate was lower in subjects with low than high δBMI (9.2% vs 14.4%, p=0.003).

CONCLUSIONS

Prediabetes conversion to diabetes could be predicted with accuracy, and weight reduction during the observation was associated with lowered conversion rate.

Trajectories of Postload Plasma Glucose in the Development of Type 2 Diabetes in Japanese Adults

We aimed to clarify how the trajectories of 1-hour postload plasma glucose (PG) and 2-hour PG were different in the development of type 2 diabetes. Using data of repeated health checkups in Japanese workers from April 2006 to March 2016, longitudinal changes of fasting, 1-hour, and 2-hour PG on the oral glucose tolerance test were analyzed with a linear mixed effects model. Of the 1464 nondiabetic subjects at baseline, 112 subjects progressed to type 2 diabetes during the observation period (progressors). In progressors, 1-hour PG and 2-hour PG showed gradual increases with slopes of 1.33 ± 0.2 and 0.58 ± 0.2 mg/dL/year, respectively, followed by a steep increase by which they attained diabetes. Until immediately before the diabetes transition, age- and sex-adjusted mean level of 2-hour PG was 149 ± 2.7 mg/dL, 34 ± 2.7 (30%) higher compared to nonprogressors, while that of 1-hour PG was 206 ± 4.1 mg/dL, 60 ± 4.3 mg/dL (41%) higher compared to nonprogressors. In conclusion, diabetes transition was preceded by a mild elevation of 2-hour PG for several years or more. The elevation in 1-hour PG was larger than that of 2-hour PG until immediately before the transition to diabetes.

One-hour plasma glucose as a predictor of the development of Type 2 diabetes in Japanese adults

AIMS

To test the hypothesis that 1-h plasma glucose in an oral glucose tolerance test is a better predictor of the development of diabetes than 2-h plasma glucose, independently of indices of insulin secretion or action in Japanese adults.

METHODS

A historical cohort study was conducted in 1445 Japanese workers who did not have diabetes. The association between 1-h plasma glucose and the development of Type 2 diabetes was analysed.

RESULTS

Overall, 95 of the study participants developed Type 2 diabetes during a mean follow-up of 4.5 years. The area under the receiver-operating characteristic curve for 1-h plasma glucose for future diabetes [0.88 (95% CI 0.84-0.91)] was greater than that for 2-h plasma glucose [0.79 (95% CI 0.74-0.84)], and for insulinogenic [0.73 (95% CI 0.68-0.78)] and disposition indices [0.79 (95% CI 0.74-0.84); P < 0.05]. Compared with the first quartile, the hazard ratio for future diabetes in the fourth quartile of 1-h plasma glucose was 42.5 [95% CI 5.7-315.2 (P < 0.05)] and the hazard ratio in the fourth quartile of 2-h plasma glucose was 4.4 [95% CI 1.8-10.8 (P < 0.05)], after adjustments for covariates including fasting plasma glucose. The significance of the elevated hazard ratio in the fourth quartile of 1-h plasma glucose was maintained after adjustments for 2-h plasma glucose, insulinogenic index or disposition index, whereas the elevation of the hazard ratio in the fourth quartile of 2-h plasma glucose was diminished and was no longer significant after adjustments for 1-h plasma glucose.

CONCLUSIONS

One-hour plasma glucose had a greater association with the future development of Type 2 diabetes than did 2-h plasma glucose, independently of oral glucose tolerance test-derived indices of insulin action in a Japanese population.

High Intensity Interval Training Improves Glycaemic Control and Pancreatic β Cell Function of Type 2 Diabetes Patients

Physical activity improves the regulation of glucose homeostasis in both type 2 diabetes (T2D) patients and healthy individuals, but the effect on pancreatic β cell function is unknown. We investigated glycaemic control, pancreatic function and total fat mass before and after 8 weeks of low volume high intensity interval training (HIIT) on cycle ergometer in T2D patients and matched healthy control individuals. Study design/method: Elderly (56 yrs±2), non-active T2D patients (n = 10) and matched (52 yrs±2) healthy controls (CON) (n = 13) exercised 3 times (10×60 sec. HIIT) a week over an 8 week period on a cycle ergometer. Participants underwent a 2-hour oral glucose tolerance test (OGTT). On a separate day, resting blood pressure measurement was conducted followed by an incremental maximal oxygen uptake (V˙O_2max) cycle ergometer test. Finally, a whole body dual X-ray absorptiometry (DXA) was performed. After 8 weeks of training, the same measurements were performed. Results: in the T2D-group, glycaemic control as determined by average fasting venous glucose concentration (p = 0.01), end point 2-hour OGTT (p = 0.04) and glycosylated haemoglobin (p = 0.04) were significantly reduced. Pancreatic homeostasis as determined by homeostatic model assessment of insulin resistance (HOMA-IR) and HOMA β cell function (HOMA-%β) were both significantly ameliorated (p = 0.03 and p = 0.03, respectively). Whole body insulin sensitivity as determined by the disposition index (DI) was significantly increased (p = 0.03). During OGTT, the glucose continuum was significantly reduced at -15 (p = 0.03), 30 (p = 0.03) and 120 min (p = 0.03) and at -10 (p = 0.003) and 0 min (p = 0.003) with an additional improvement (p = 0.03) of its 1^st phase (30 min) area under curve (AUC). Significant abdominal fat mass losses were seen in both groups (T2D: p = 0.004 and CON: p = 0.02) corresponding to a percentage change of -17.84%±5.02 and -9.66%±3.07, respectively. Conclusion: these results demonstrate that HIIT improves overall glycaemic control and pancreatic β cell function in T2D patients. Additionally, both groups experienced abdominal fat mass losses. These findings demonstrate that HIIT is a health beneficial exercise strategy in T2D patients.

An inverse U-shaped association of late and peak insulin levels during an oral glucose load with glucose intolerance in a Japanese population: a cross-sectional study

The current study investigated the association of post-load insulin levels with glucose tolerance in a Japanese population. A total of 1450 Japanese employees who underwent a 75-g oral glucose tolerance test (OGTT) were included. Glucose tolerance was assessed by 120-min glucose levels during a 75-g OGTT. A penalized cubic regression spline model analysis revealed that the 60- and 120-min insulin levels, but not 0- or 30-min insulin levels, had an inverse U-shaped relationship to the 120-min glucose level. Furthermore, peak insulin level followed an inverse U shape in relation to the 120-min glucose level, whereas the peak of insulin appeared at a later point in time as the 120-min glucose level increased. These associations were similarly observed in both obese and non-obese subgroups, although obesity was associated with higher insulin levels. Peak insulin levels also demonstrated an inverse U shape in association with 0-min glucose levels and indices of β cell function, assessed by the disposition index and the β-cell function index. In conclusion, peak insulin levels followed an inverse U shape in relation to glucose intolerance in a Japanese population, whereas the impairment of glucose tolerance was associated with a delay in the time to reach peak insulin levels.

Impact of one-hour postchallenge glucose on the relationship between insulin sensitivity and secretion

The impact of postchallenge glucose on the relationship between insulin sensitivity (SI) and secretion (β) is unknown. We analyzed data from 2,264 health examinees (male/female 1,524/740, median age 54 yrs) with normal glucose tolerance (NGT, n = 1,623), non-diabetic hyperglycemia (NDH, n = 555), or diabetes (DM, n = 86) using OGTT-derived indices of SI (insulin sensitivity index [ISI]-Matsuda, 1/HOMA-IR, and 1/fasting IRI) and β (δIRI0-30/δPG0-30, and Stumvoll 1st [Stumvoll-1] and 2nd [Stumvoll-2] phases). The combination of 1/HOMA-IR and Stumvoll-1 recapitulated the hyperbolic SI-β relationship with the slope of the fitted line -1.000 in NGT subjects, and therefore it was utilized in the following analysis of the SI-β correlation. In multiple regression analysis of the relationship between SI and β, an independent correlation was found for 1 h-plasma glucose (PG; PG60) but not for 2 h-PG. When the NGT subjects were grouped by PG60 quartile (Q), the fitted line was flat in Q1 but progressively steeper from Q2 to Q4, with a slope (95%CI) of -0.663 (-0.726~-0.605), -0.680 (-0.745~-0.622), -0.847 (-0.922~-0.779), and -1.259 (-1.370~-1.158) (P for trend < 0.05). The fitted line steepened further in the NDH and DM groups, with a slope of -1.545 and -1.915, respectively (P < 0.01 for the difference). The intercept of the fitted line for SI-β correlation was also progressively lower across the PG60 Q for NGT, NDH, and DM. In conclusion, using the 1/HOMA-IR-Stumvoll-1 pair for an analysis of the SI-β relationship, elevated PG60 was associated with steepening and downward shifting of the fitted line for the SI-β correlation. The finding suggests impaired beta cell function.

Effect of Cinnamon Tea on Postprandial Glucose Concentration

Glycaemic control, in particular at postprandial period, has a key role in prevention of different diseases, including diabetes and cardiovascular events. Previous studies suggest that postprandial high blood glucose levels (BGL) can lead to an oxidative stress status, which is associated with metabolic alterations. Cinnamon powder has demonstrated a beneficial effect on postprandial glucose homeostasis in animals and human models. The purpose of this study is to investigate the effect of cinnamon tea (C. burmannii) on postprandial capillary blood glucose level on nondiabetic adults. Participants were given oral glucose tolerance test either with or without cinnamon tea in a randomized clinical trial. The data revealed that cinnamon tea administration slightly decreased postprandial BGL. Cinnamon tea ingestion also results in a significantly lower postprandial maximum glucose concentration and variation of maximum glucose concentration (p < 0.05). Chemical analysis showed that cinnamon tea has a high antioxidant capacity, which may be due to its polyphenol content. The present study provides evidence that cinnamon tea, obtained from C. burmannii, could be beneficial for controlling glucose metabolism in nondiabetic adults during postprandial period.

Impact of serum triglyceride and high density lipoprotein cholesterol levels on early-phase insulin secretion in normoglycemic and prediabetic subjects

BACKGROUND

Increased triglycerides (TGs) and decreased high density lipoprotein cholesterol (HDL-C) levels are established as diabetic risks for nondiabetic subjects. The aim of this study was to investigate the relationship among TG, HDL-C, TG/HDL-C ratio, and early-phase insulin secretion in normoglycemic and prediabetic subjects.

METHODS

We evaluated 663 Japanese subjects who underwent the 75-g oral glucose tolerance test. On the basis of these results, the subjects were divided into four groups: those with normal glucose tolerance (NGT; n=341), isolated impaired fasting glucose (i-IFG; n=211), isolated impaired glucose tolerance (i-IGT; n=71), and combined IFG and IGT (IFG+IGT; n=40). Insulin secretion was estimated by the insulinogenic index (IGI) (Δinsulin/Δglucose [30 to 0 minutes]) and disposition index (DI) (IGI/homeostasis model assessment of insulin resistance).

RESULTS

In prediabetic subjects (i-IFG, i-IGT, and IFG+IGT), linear regression analyses revealed that IGI and DI were positively correlated with HDL-C levels. Moreover, in subjects with i-IGT and (IFG+IGT), but not with i-IFG, the indices of insulin secretion were negatively correlated with the log-transformed TG and TG/HDL-C ratio. In both the subjects with i-IGT, multivariate linear regression analyses revealed that DI was positively correlated with HDL-C and negatively with log-transformed TG and TG/HDL-C ratio. On the other hand, in subjects with NGT, there was no association between insulin secretion and lipid profiles.

CONCLUSION

These results revealed that serum TG and HDL-C levels have different impacts on early-phase insulin secretion on the basis of their glucose tolerance status.

Glycemic variability in normal glucose regulation subjects with elevated 1-h postload plasma glucose levels

Subjects with normal glucose regulation (NGR), whose 1-h postload plasma glucose is ≥8.6 mmol/L (155 mg/dL, NGR 1 h ≥ 8.6) during 75-g oral glucose tolerance test (OGTT), have an increased risk of type 2 diabetes and subclinical organ damage. And, the deficiency in islet β cell function is responsible for glycemic disorders. The purpose of this study is to investigate glycemic variability in NGR subjects with elevated 1-h postload plasma glucose levels and its association with islet β cell function. The 29 NGR subjects with 1-h postload plasma glucose ≥8.6 mmol/L (NGR 1 h ≥ 8.6) and 29 age- and sex-matched NGR subjects with 1-h postload plasma glucose <8.6 mmol/L (NGR 1 h < 8.6) were recruited in the study. Insulin sensitivity (Matsuda index, ISI), insulin secretion (insulinogenic index ΔI30/ΔG30), and integrated β cell function measured by the oral disposition index (ΔI30/ΔG30 multiplied by the ISI) were derived from OGTT. All subjects were monitored using the continuous glucose monitoring system for consecutive 72 h. The multiple parameters of glycemic variability included the standard deviation of blood glucose (SDBG), mean blood glucose (MBG), mean of daily differences (MODD), and mean amplitude of glycemic excursions (MAGE). MAGE is considered as a gold standard of glycemic variability. Glycemic variability parameters SDBG, MBG, MODD, and MAGE in NGR 1 h ≥ 8.6 group were higher than those in NGR 1 h < 8.6 group (p < 0.05), and oral disposition index in NGR 1 h ≥ 8.6 group was lower than that in NGR 1 h < 8.6 group (p < 0.05). SDBG, MBG, MODD, MAGE, and 1-h postload plasma glucose all negatively associated with oral disposition index in the separate group (p < 0.05) and in the whole subjects (p < 0.05). After multivariate regression analysis, oral disposition index was the strongest independent contributor to MAGE and 1-h postload plasma glucose in the separate group (p < 0.05) and in the whole subjects (p < 0.05). It is concluded that NGR 1 h ≥ 8.6 group had higher glycemic variability and lower oral disposition index, compared with NGR 1 h < 8.6 group. Increased glycemic variability parameters and elevated 1-h postload plasma glucose consistently associated with declined oral disposition index in subjects from NGR 1 h < 8.6 to NGR 1 h ≥ 8.6 group.

Longitudinal changes in insulin sensitivity, insulin secretion, beta cell function and glucose effectiveness during development of non-diabetic hyperglycemia in a Japanese population

Since there had been no previous studies of alterations in insulin sensitivity, glucose-stimulated insulin secretion, beta cell function and glucose effectiveness during the development of non-diabetic hyperglycemia in Asian populations, we conducted a longitudinal study of such changes in 244 Japanese adults with normal glucose tolerance (median BMI 23.3 kg/m² and age 51 yrs). The median follow-up period was 3.3 yrs. One hundred and eighty-two subjects maintained normal glucose tolerance (nonprogressors). After excluding the 3 subjects who progressed to diabetes, we analyzed the 59 who developed non-diabetic hyperglycemia (progressors), of which 31 progressed to impaired fasting glucose and 28 to impaired glucose tolerance. Whole body insulin sensitivity was estimated by ISI_Matsuda, glucose-stimulated insulin secretion by [δIRI_0-30/δPG_0-30] and Stumvoll indices, hepatic insulin sensitivity by quantitative insulin sensitivity check index (QUICKI) and 1/fasting IRI, beta cell function by oral disposition index (DI_O) ([δIRI_0-30/δPG_0-30]∙[ISI_Matsuda]), and glucose effectiveness by an OGTT-derived index (SgI_O). ISI_Matsuda (p <0.05), [δIRI_0-30/δPG_0-30], DI_O and SgI_O (both p <0.01), but not QUICKI, 1/fasting IRI, or Stumvoll-1st and -2nd phases, were lower in the progressors at baseline. This group was also characterized by the following: 1) ISI_Matsuda, DI_O and SgI_O were reduced by 34%, 32% and 11%, respectively (all p <0.01); 2) QUICKI and 1/fasting IRI diminished by 21% and 5%, respectively (both p <0.01); and 3) no significant changes were found in [δIRI_0-30/δPG_0-30], Stumvoll-1st and -2nd phases or BMI during the follow-up. In the nonprogressors, no indices changed significantly during the follow-up. Our study concluded that during the transition from normal glucose tolerance to non-diabetic hyperglycemia in this non-obese population, whole body insulin sensitivity, hepatic insulin sensitivity, beta cell function, and glucose effectiveness were all attenuated, but no significant changes in glucose-stimulated insulin secretion occurred. Also of note is the fact that the transition took place without any accompanying increase in BMI.

Relationship and factors responsible for regulating fasting and post-challenge plasma glucose levels in the early stage development of type 2 diabetes mellitus

AIMS/INTRODUCTION

Elevation of 2-h plasma glucose (2-h PG) levels keeps step with fasting plasma glucose (FPG) levels elevation, but some individuals show dominant elevation of 2-h PG and others FPG. We analyzed dependent and independent relationships between 2-h PG and FPG, and investigated the factors regulating 2-h PG and FPG.

MATERIALS AND METHODS

In 1,657 Japanese participants who underwent a 75-g oral glucose tolerance test at the initial examination for a medical check-up, we carried out simple linear regression analysis between 2-h PG and FPG levels on the three patterns of independent variables. We divided the participants into two subgroups: the 2-h PG-side group and the FPG-side from the regression line, and examined the relationships between 2-h PG-FPG and factors responsible for elevation of plasma glucose levels.

RESULTS

There was a significant positive correlation between 2-h PG and FPG levels. The regression line of both 2-h PG and FPG as independent variables was in accordance with the regression line of 2-h PG as an independent variable and FPG as a dependent variable. In 2-h PG-side group, age was the independent factor affecting 2-h PG in addition to insulinogenic index and insulin sensitivity index (ISI composite). In the FPG-side group, triglyceride was the independent factor affecting FPG in addition to insulinogenic index and ISI composite.

CONCLUSIONS

Two-hour PG was an independent predictor of FPG. In addition to the importance of decreased insulin secretion and insulin sensitivity, age was the strong factor to elevate 2-h PG levels in the 2-h PG-side group and triglyceride was the strong factor to elevate FPG levels in the FPG-side group in the early stage of development of type 2 diabetes.

Elevated liver enzymes are related to progression to impaired glucose tolerance in Japanese men

AIMS

To investigate whether the elevation of liver enzymes is associated with the progression from normal to impaired glucose tolerance.

METHODS

A historical cohort study was conducted in 594 male workers at public schools, who had normal glucose tolerance at baseline. The progression to impaired glucose tolerance and impaired fasting glycaemia during a mean follow-up of 3.1 years was measured using an oral glucose tolerance test.

RESULTS

Overall, 141 (23.7%) subjects developed impaired glucose tolerance and 68 (11.4%) subjects developed impaired fasting glycaemia, 23 of whom had combined impaired fasting glycaemia/impaired glucose tolerance. The incidence of impaired glucose tolerance increased significantly with increasing quartiles of serum aspartate aminotransferase, alanine aminotransferase and γ-glutamyltransferase (P for trend <0.01). In Cox proportional hazards regression analysis, after adjusting for comprehensive risk factors, including plasma glucose levels, BMI and homeostatic model assessment of insulin resistance, the risk of progression to impaired glucose tolerance was significantly higher in the highest quartile of alanine aminotransferase than in the lowest quartile (hazard ratio 2.5; 95% CI 1.1-5.7). A significant association between alanine aminotransferase and the progression to impaired glucose tolerance was found after further adjustments for other liver enzymes or after the sample was limited to those with BMI < 25.0 kg/m(2) or with fasting plasma glucose < 5.5 mmol/l.

CONCLUSIONS

A higher level of alanine aminotransferase was independently associated with progression from normal to impaired glucose tolerance in Japanese men. The elevation of alanine aminotransferase may be a change that occurs early in the evolution of diabetes.

Age-associated changes of islet endocrine cells and the effects of body mass index in Japanese

AIMS/INTRODUCTION

Impaired growth and premature death of β-cells are implicated in the progression of islet pathology in type 2 diabetes. It remains unclear, however, how aging affects islet cells, or whether the islet change in diabetes is an augmented process of aging. We studied age-related changes of the islet structure in Japanese non-diabetic subjects and explored the underlying mechanism of the changes.

MATERIALS AND METHODS

A total of 115 non-diabetic autopsy cases were subjected to morphometric analysis for volume densities of islets, β- and non-β-cells, as well as their masses. Proliferation activity identified by Ki67, and expressions of pancreatic and duodenal homeobox (PDX)-1, cell cycle inhibitor P16, and oxidative stress marker γH2AX were also examined.

RESULTS

There was a gradual and marginal decline of volume densities of islets, β- and non-β-cells with aging, while masses of these components were increased during maturation and slowly decreased after the 40s. Islet density was high in the young, but reduced after maturation. There was only a minimal influence of increased body mass index (BMI) on the increase in β-cell mass, but not on the other variables. Ki67 positivity and PDX-1 expressions were high in the young, but low after maturation, whereas expressions of P16 and γH2AX were elevated in the aged.

CONCLUSIONS

Age-associated decline of β-cell mass is marginal after maturation, and the reduction of β-cell mass could be a specific process in diabetes. The impact of BMI on the islet structure is limited in Japanese with normal glucose tolerance.

The evolution of non-diabetic hyperglycemia: a longitudinal study

The risk factors for impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) have yet to be established. Our aim was to elucidate the predisposing factors for IFG and IGT in Japanese subjects with normal glucose tolerance (NGT). Using a 75 g oral glucose tolerance test (OGTT), we analyzed 604 adults with the ADA-defined NGT. Follow-up glucose tolerance status was determined by 75 g OGTT performed 3.7 yrs later. Glucose-stimulated insulin secretion (GSIS), whole body insulin sensitivity (SI) and beta cell function (BCF) were estimated by Stumvoll indices, ISI(Matsuda), and a product of Stumvoll 1(st) and ISI(Matsuda), respectively, and hepatic SI by quantitative insulin sensitivity check index. Logistic regression analysis revealed that attenuated BCF due to low GSIS was an independent risk factor for IFG. Low whole body SI was an additional risk for IGT. Male gender and high BMI were independently related to the progression to both IFG and IGT, whereas a positive diabetes family history was independently related to IGT. The worsening of glucose tolerance at large was predicted with 66% sensitivity by risk engine with GSIS, whole body SI, gender, BMI and glucose. This finding may help when implementing early intervention strategies for diabetes.

Prediction of the presence of insulin resistance using general health checkup data in Japanese employees with metabolic risk factors

AIM

The aim of the current study was to develop a predictive model of insulin resistance using general health checkup data in Japanese employees with one or more metabolic risk factors.

METHODS

We used a database of 846 Japanese employees with one or more metabolic risk factors who underwent general health checkup and a 75-g oral glucose tolerance test (OGTT). Logistic regression models were developed to predict existing insulin resistance evaluated using the Matsuda index. The predictive performance of these models was assessed using the C statistic.

RESULTS

The C statistics of body mass index (BMI), waist circumference and their combined use were 0.743, 0.732 and 0.749, with no significant differences. The multivariate backward selection model, in which BMI, the levels of plasma glucose, high-density lipoprotein (HDL) cholesterol, log-transformed triglycerides and log-transformed alanine aminotransferase and hypertension under treatment remained, had a C statistic of 0.816, with a significant difference compared to the combined use of BMI and waist circumference (p＜0.01). The C statistic was not significantly reduced when the levels of log-transformed triglycerides and log-transformed alanine aminotransferase and hypertension under treatment were simultaneously excluded from the multivariate model (p=0.14). On the other hand, further exclusion of any of the remaining three variables significantly reduced the C statistic (all p＜0.01).

CONCLUSIONS

When predicting the presence of insulin resistance using general health checkup data in Japanese employees with metabolic risk factors, it is important to take into consideration the BMI and fasting plasma glucose and HDL cholesterol levels.

Postload hyperglycemia is associated with increased subclinical inflammation in patients with prediabetes

BACKGROUND/AIMS

In this present study, we aimed: (i) To clarify if prediabetes is associated with subclinical inflammation independent of underlying obesity, and (ii) to evaluate the effect of postload glucose concentration on subclinical inflammation markers in a group of patients with elevated fasting glucose.

MATERIAL AND METHODS

In a cohort of 165 patients with newly detected fasting hyperglycemia, according to 75 g oral glucose tolerance test (OGTT), subjects were classified either as newly diagnosed type 2 diabetes (diabetes group, n = 40), impaired fasting glucose (IFG) plus impaired glucose tolerance (IGT) (IFG/IGT group, n = 42) or IFG only (IFG group, n = 83). A control group (n = 47) consisted of age- and body mass index (BMI)-matched healthy subjects with a normal OGTT. Circulating concentrations of lipids, insulin, interleukin-6 (IL-6), interleukin-8 (IL-8) and high sensitive C-reactive protein (hsCRP) were measured. HOMA index was calculated.

RESULTS

Subclinical inflammation markers were elevated in patients with diabetes and IFG/IGT compared to healthy controls and also IFG patients (diabetes vs. control: p < 0.05 for hsCRP, IL-8, and IL-6; IFG/IGT vs. control: p < 0.05 for hsCRP, and IL-6; diabetes vs. IFG: p < 0.05 for hsCRP, and IL-6; IFG/IGT vs. IFG: p < 0.05 for hsCRP, and IL-6). In multiple regression analysis, postload glucose concentration was independently associated with circulating hsCRP and IL-6 concentrations when the data was controlled for age, gender, BMI and lipid concentrations (p < 0.05 for hsCRP, and IL-6).

CONCLUSION

Our results suggest that patients with prediabetes, independent of underlying obesity, have increased concentrations of subclinical inflammation which is mostly driven by postload glucose concentrations.

Glycemic variability in gestational diabetes mellitus and its association with β cell function

Maternal hyperglycemia in gestational diabetes mellitus (GDM), especially hyperglycemic excursions, is associated with increased risks of adverse pregnancy outcomes. Continuous glucose monitoring (CGM) system (CGMS) is better than intermittent self-measurements in detecting detailed glucose profiles on the magnitude and duration of glucose fluctuations. Hyperglycemia resulted from impaired β cell function. This study analyzed the characteristics of glycemic variability in GDM with 24-28 gestational weeks and its association with β cell function. Thirty GDM with 24-28 gestational weeks (GDM group) were included in this study, and 20 normal gestational women (NGW group) and 20 normal glucose regulation non-pregnant women (NGRW group) were set as controls. The three groups were monitored using the CGMS for consecutive 72 h. The parameters of glycemic variability included the standard deviation of blood glucose (SDBG), mean of continuous 24-h blood glucose (MBG), mean amplitude of glycemic excursions (MAGEs), and mean of daily differences (MODDs). Homeostasis model assessments were applied to access the insulin resistance (HOMA-IR). The early insulinogenic index (ΔI30/ΔG30) and the area under the curve of insulin (AUCI180) derived from 75-g oral glucose tolerance test were applied to evaluate the early-phase insulin secretion and second-phase insulin secretion, respectively. After CGM, MAGE and MBG value increased progressively from NGRW, NGW to GDM group (p < 0.05); MODD and SDBG values of GDM group were all higher than those of NGRW and NGW groups (p < 0.05), but there are no differences in MODD and SDBG between NGRW and NGW groups (p > 0.05). After comparison of β cell function, ΔI30/ΔG30 decreased progressively from NGRW, NGW to GDM group (p < 0.05); HOMA-IR and AUCI180 increased progressively from NGRW, NGW to GDM group (p < 0.05). MAGE value was correlated with ΔI30/ΔG30 and HOMA-IR in GDM group (r = -0.78 and 0.65, respectively, p < 0.05). Multiple linear stepwise regression analysis showed that ΔI30/ΔG30 and HOMA-IR were the independent factors of MAGE (β = -0.61, 0.34, respectively, p < 0.05). Glycemic variability in GDM was higher than in normal pregnant women, and glycemic variability evaluated by MAGE correlates well with impaired early-phase insulin secretion in GDM. Further large-scale studies are needed to formulate treatment strategies to make up for the impaired early-phase insulin secretion and flat glycemic variability, and analyze the association between pregnancy outcomes improvement and glycemic variability remission in GDM.

Pancreatic beta cell function in lean and obese Japanese with various degrees of glucose tolerance

The aim of the current study was to investigate whether obese subjects have different insulin secretory capacity compared to lean subjects with the same glucose tolerance in a Japanese population. We included a total of 1749 Japanese employees who underwent 75-g oral glucose tolerance test (OGTT). The study population was divided into deciles of 120-min glucose levels and the indices of insulin secretion and insulin sensitivity in each decile were compared between the subjects with and without obesity (body mass index ≥ 25 kg/m2). The indices used in the current study were Matsuda index, insulinogenic index, and disposition index. Obese subjects had significantly lower values of Matsuda index and significantly higher value of insulinogenic index than non-obese subjects in every decile (all p < 0.05). On the other hand, disposition index was not significantly different between non-obese and obese subjects in any decile of 120-min glucose level (all p > 0.05). Similar findings were observed when the study population was classified by waist circumference. In conclusion, disposition index derived from the data of 75-g OGTT was similarly decreased in obese Japanese subjects compared to non-obese Japanese subjects with the same post-load glucose levels. Future studies will be needed to confirm whether the development of glucose intolerance in obese Japanese subjects is accompanied by the same degree of pancreatic beta cell dysfunction as non-obese Japanese subjects.

Glycemic variability in relation to oral disposition index in the subjects with different stages of glucose tolerance

BACKGROUND

Glucose variability could be an independent risk factor for diabetes complications in addition to average glucose. The deficiency in islet β cell secretion and insulin sensitivity, the two important pathophysiological mechanisms of diabetes, are responsible for glycemic disorders. The oral disposition index evaluated by product of insulin secretion and sensitivity is a useful marker of islet β cell function. The aim of the study is to investigate glycemic variability in relation to oral disposition index in the subjects across a range of glucose tolerance from the normal to overt type 2 diabetes.

METHODS

75-g oral glucose tolerance test (OGTT) was performed in total 220 subjects: 47 with normal glucose regulation (NGR), 52 with impaired glucose metabolism (IGM, 8 with isolated impaired fasting glucose [IFG], 18 with isolated impaired glucose tolerance [IGT] and 26 with combined IFG and IGT), 61 screen-diagnosed diabetes by isolated 2-h glucose (DM2h) and 60 newly diagnosed diabetes by both fasting and 2-h glucose (DM). Insulin sensitivity index (Matsuda index, ISI), insulin secretion index (ΔI30/ΔG30), and integrated β cell function measured by the oral disposition index (ΔI30/ΔG30 multiplied by the ISI) were derived from OGTT. All subjects were monitored using the continuous glucose monitoring system for consecutive 72 hours. The multiple parameters of glycemic variability included the standard deviation of blood glucose (SD), mean of blood glucose (MBG), high blood glucose index (HBGI), continuous overlapping net glycemic action calculated every 1 h (CONGA1), mean of daily differences (MODD) and mean amplitude of glycemic excursions (MAGE).

RESULTS

From the NGR to IGM to DM2h to DM group, the respective values of SD (mean ± SD) (0.9 ± 0.3, 1.5 ± 0.5, 1.9 ± 0.6 and 2.2 ± 0.6 mmol/), MBG (5.9 ± 0.5, 6.7 ± 0.7, 7.7 ± 1.0 and 8.7 ± 1.5 mmol/L), HGBI [median(Q1-Q3)][0.8(0.2-1.2), 2.0(1.2-3.7), 3.8(2.4-5.6) and 6.4(3.2-9.5)], CONGA1 (1.0 ± 0.2, 1.3 ± 0.2, 1.5 ± 0.3 and 1.8 ± 0.4 mmol/L), MODD (0.9 ± 0.3, 1.4 ± 0.4, 1.8 ± 0.7 and 2.1 ± 0.7 mmol/L) and MAGE (2.1 ± 0.6, 3.3 ± 1.0, 4.3 ± 1.4 and 4.8 ± 1.6 mmol/L) were all increased progressively (all p < 0.05), while their oral disposition indices [745(546-947), 362(271-475), 203(134-274) and 91(70-139)] were decreased progressively (p < 0.05). In addition, SD, MBG, HGBI, CONGA1, MODD and MAGE were all negatively associated with the oral disposition index in each group (all p < 0.05) and in the entire data set (r = -0.66, -0.66, -0.72, -0.59, -0.61 and -0.65, respectively, p < 0.05).

CONCLUSIONS

Increased glycemic variability parameters are consistently associated with decreased oral disposition index in subjects across the range of glucose tolerance from the NGR to IGM to DM2h to DM group.