Insulin secretion and action show differences in impaired fasting glucose and in impaired glucose tolerance in Asian Indians

Prevalence and correlates of pre-diabetes in adults of mixed ethnicities in the South African population: A systematic review and meta-analysis

INTRODUCTION

Pre-diabetes is a metabolic condition characterised by moderate glycaemic dysregulation and is a frontline risk factor for multiple metabolic complications such as type 2 diabetes mellitus. To the best of our knowledge, this will be the first systematic review and meta-analysis focusing on generating a comprehensive pooling of studies reporting on pre-diabetes prevalence in South Africa. Therefore, the review's purpose will be to screen and select reports that can be used to synthesise and provide the best estimate prevalence of pre-diabetes and its associated correlates in the South African population.

METHODS AND ANALYSIS

To determine the prevalence and correlates of pre-diabetes in South Africa, we searched PubMed, Web of Science, Google scholar and African Journal online for published or unpublished studies reporting the prevalence of pre-diabetes in South Africa starting from the year 2000 to 2020. Studies were assessed for eligibility by checking if they met the inclusion criteria.

RESULTS & CONCLUSION

The total number of studies deemed eligible is 13 and from these studies, an overall prevalence of pre-diabetes was reported to be 15,56% in the South African population. Hypertension, obesity and sedentary lifestyle were the common correlates recorded for the population of interest. Therefore, the review highlights the disturbingly high prevalence of pre-diabetes in South Africa and necessitates further investigations into the possible genetics, biochemical and hormonal changes in pre-diabetes.

ETHICS AND DISSEMINATION

The review will not require ethics clearance because non-identifiable data will be used. The review outcomes will give insight into the current burden that pre-diabetes has in South Africa.

PROSPERO REGISTRATION NUMBER

CRD42020182430.

Associations of the HOMA2-%B and HOMA2-IR with progression to diabetes and glycaemic deterioration in young and middle-aged Chinese

AIMS

Insulin deficiency (ID) and resistance (IR) contribute to progression from normal glucose tolerance to diabetes to insulin requirement although their relative contributions in young-onset diabetes is unknown.

METHODS

We examined the associations of HOMA2 using fasting plasma glucose and C-peptide in Chinese aged 20-50 years with (1) progression to type 2 diabetes (T2D) in participants without diabetes in a community-based cohort (1998-2013) and (2) glycaemic deterioration in patients with T2D in a clinic-based cohort (1995-2014). We defined ID as HOMA2-%B below median and insulin IR as HOMA2-IR above median.

RESULTS

During 10-year follow-up, 62 (17.9%) of 347 community-dwelling participants progressed to T2D. After 8.6 years, 291 (48.1%) of 609 patients with T2D had glycaemic deterioration. At baseline, progressors for T2D had higher HOMA2-IR, while in patients with T2D, progressors for glycaemic deterioration had higher HOMA2-IR and lower HOMA2-%B than non-progressors. The non-ID/IR group and the ID/IR group had an adjusted odds ratios of 2.47 (95% CI: 1.28, 4.94) and 5.36 (2.26, 12.79), respectively, for incident T2D versus the ID/non-IR group. In patients with T2D, 50% of the ID/IR group required insulin at 6.7 years versus around 11 years in the non-ID/IR or ID/non-IR, and more than 15 years in the non-ID/non-IR group. Compared with the latter group, the adjusted hazard ratios were 2.74 (1.80, 4.16) in the ID/non-IR, 2.73 (1.78, 4.19) in the non-ID/IR and 4.46 (2.87, 6.91) in the ID/IR group (p-interaction = 0.049).

CONCLUSIONS

In young Chinese adults, IR and ID contributed to progression to T2D and glycaemic deterioration.

Comparison of islet cell function, insulin sensitivity, and incretin axis between Asian-Indians with either impaired fasting glucose or impaired glucose tolerance, and normal healthy controls

AIMS

The objective of this study was to compare the islet cell function, insulin sensitivity, and incretin axis between Asian-Indian subjects with either impaired fasting glucose (IFG), or impaired glucose tolerance (IGT), and normal glucose tolerance (NGT).

MATERIALS AND METHODS

Prediabetes subjects underwent a mixed meal tolerance test(MMTT) after overnight fasting. Samples for glucose, insulin, glucagon, and glucagon-like peptide-1 (GLP-1) were collected at 0, 30, 60, and 120 min. Insulin secretion sensitivity index -2 (ISSI-2) for beta-cell function and Matsuda index for insulin sensitivity were assessed. Alpha cell function was assessed by measuring the area under the curve (AUC) _0-120 glucagon/AUC_0-120 glucose.

RESULTS

A total of sixty subjects were recruited with 20 in each group. The beta-cell function represented by ISSI-2 was impaired in prediabetes subjects as compared to NGT group (IFG: 2.09 ± 0.44 vs. NGT: 3.04 ± 0.80, P < 0.0001, and IGT: 2.33 ± 0.59 vs. NGT: 3.04 ± 0.80, P = 0.002). Similarly, AUC_0-120 glucagon/AUC_0-120 glucose was also lower in prediabetes group as compared to healthy controls (IFG: 0.41(0.54) vs. NGT: 1.07(0.39), P = 0.003 and IGT: 0.57(0.38) vs. NGT: 1.07(0.39), P = 0.001).

CONCLUSION

Asian-Indian prediabetes subjects have reduced beta-cell function with lesser glucagon secretion during MMTT as compared to normal healthy controls.

The "A to Z" of Managing Type 2 Diabetes in Culturally Diverse Populations

Type 2 diabetes affects racial/ethnic minorities at an alarming rate in the US and in many countries around the world. The quality of health care provided to these groups is often suboptimal, resulting in worse patient-related outcomes when compared to those in mainstream populations. Understanding the complex biological elements that influence the development and course of the disease in high-risk populations is extremely important but often insufficient to implement effective prevention and treatment plans. Multiple factors must be addressed in routine diabetes clinical care. This paper discusses various key factors, organized in alphabetical order. These are acculturation, biology, clinician's cultural awareness, depression and diabetes-specific emotional distress, educational level, fears, group integration, health literacy, intimacy and sexual dysfunction, judging, knowledge of the disease, language, medication adherence, nutritional preferences, other forms of medicine (alternative), perception of body image, quality of life, religion and faith, socio-economic status, technology, unconscious bias, vulnerable groups, asking why?, exercise, "you are in charge" and zip it! Considering these factors in the development of type 2 diabetes prevention and treatment programs will help improve diabetes-related outcomes in culturally diverse populations and reduce health care disparities.

Strong association between insulin-mediated glucose uptake and the 2-hour, not the fasting plasma glucose concentration, in the normal glucose tolerance range

AIM

The aim of this study was to examine the relationship between whole-body insulin-mediated glucose disposal and the fasting plasma glucose concentration in nondiabetic individuals.

RESEARCH DESIGN AND METHODS

Two hundred fifty-three nondiabetic subjects with normal glucose tolerance (NGT), impaired fasting glucose (IFG), impaired glucose tolerance, and combined glucose intolerance received a 75-g oral glucose tolerance test and euglycemic hyperinsulinemic clamp. Total glucose disposal (TGD) during the insulin clamp was compared in IFG and NGT individuals and was related to fasting and 2-hour plasma glucose concentrations in each group.

RESULTS

TGD varied considerably between NGT and IFG individuals and displayed a strong inverse relationship with the 2-hour plasma glucose (PG; r = 0.40, P < .0001) but not with the fasting PG. When IFG and NGT individuals were stratified based on their 2-hour PG concentration, the increase in 2-hour PG was associated with a progressive decrease in TGD in both groups, and the TGD was comparable among NGT and IFG individuals.

CONCLUSION

The present results indicate the following: 1) as in NGT, insulin-stimulated TGD varies considerably in IFG individuals; 2) the large variability in TGD in IFG and NGT individuals is related to the 2-hour PG concentration; and 3) after adjustment for the 2-hour proglucagon concentration, IFG subjects have comparable TGD with NGT individuals.

Insulin sensitivity and secretion in Arab Americans with glucose intolerance

BACKGROUND

This study examined the pathophysiological abnormalities in Arab Americans with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT).

SUBJECTS AND METHODS

Homeostasis model assessment of insulin resistance (HOMA-IR), homeostasis model assessment of insulin secretion (HOMA-%β), and the Matsuda Insulin Sensitivity Index composite (ISIcomposite) were calculated from the fasting and stimulated glucose and insulin concentrations measured during the oral glucose tolerance test in a population-based, representative, cross-sectional sample of randomly selected Arab Americans.

RESULTS

In total, 497 individuals (42±14 years old; 40% males; body mass index [BMI], 29±6 kg/m(2)) were studied. Multivariate linear regression models were performed to compare HOMA-IR, HOMA-%β, and ISIcomposite among individuals with normal glucose tolerance (NGT) (n=191) versus isolated IFG (n=136), isolated IGT (n=22), combined IFG/IGT (n=43), and diabetes (n=105). Compared with individuals with NGT (2.9±1.6), HOMA-IR progressively increased in individuals with isolated IFG (4.8±2.7, P<0.001), combined IFG/IGT (6.0±4.3, P<0.001), and diabetes (9.7±8.3, P<0.001) but not in those with isolated IGT (3.0±1.7, P=0.87). After adjustment for sex and BMI, these associations remained unchanged. Whole-body insulin sensitivity as measured by ISIcomposite was significantly lower in individuals with isolated IFG (3.9±2.3, P<0.001), isolated IGT (2.8±1.5, P<0.001), combined IFG/IGT (1.9±1.1, P<0.001), and diabetes (1.6±1.1, P<0.001) compared with those with NGT (6.1±3.5). HOMA-%β was significantly lower in diabetes (113.7±124.9, P<0.001) compared with NGT (161.3±92.0). After adjustment for age, sex, and BMI, isolated IFG (146.6±80.2) was also significantly associated with a decline in HOMA-%β relative to NGT (P=0.005).

CONCLUSIONS

This study suggests that differences in the underlying metabolic defects leading to diabetes in Arab Americans with IFG and/or IGT exist and may require different strategies for the prevention of diabetes.

Evidence of reduced β-cell function in Asian Indians with mild dysglycemia

OBJECTIVE

To examine β-cell function across a spectrum of glycemia among Asian Indians, a population experiencing type 2 diabetes development at young ages despite low BMI.

RESEARCH DESIGN AND METHODS

One-thousand two-hundred sixty-four individuals without known diabetes in the Diabetes Community Lifestyle Improvement Program in Chennai, India, had a 75-g oral glucose tolerance test, with glucose and insulin measured at 0, 30, and 120 min. Type 2 diabetes, isolated impaired fasting glucose (iIFG), isolated impaired glucose tolerance (iIGT), combined impaired fasting glucose and impaired glucose tolerance, and normal glucose tolerance (NGT) were defined by American Diabetes Association guidelines. Measures included insulin resistance and sensitivity (homeostasis model assessment of insulin resistance [HOMA-IR], modified Matsuda Index, 1/fasting insulin) and β-cell function (oral disposition index = [Δ insulin0-30/Δ glucose 0-30] × [1/fasting insulin]).

RESULTS

Mean age was 44.2 years (SD, 9.3) and BMI 27.4 kg/m(2) (SD, 3.8); 341 individuals had NGT, 672 had iIFG, IGT, or IFG plus IGT, and 251 had diabetes. Patterns of insulin resistance or sensitivity were similar across glycemic categories. With mild dysglycemia, the absolute differences in age- and sex-adjusted oral disposition index (NGT vs. iIFG, 38%; NGT vs. iIGT, 32%) were greater than the differences in HOMA-IR (NGT vs. iIFG, 25%; NGT vs. iIGT, 23%; each P < 0.0001). Compared with NGT and adjusted for age, sex, BMI, waist circumference, and family history, the odds of mild dysglycemia were more significant per SD of oral disposition index (iIFG: odds ratio [OR], 0.36; 95% CI, 0.23-0.55; iIGT: OR, 0.37; 95% CI, 0.24-0.56) than per SD of HOMA-IR (iIFG: OR, 1.69; 95% CI, 1.23-2.33; iIGT: OR, 1.53; 95% CI, 1.11-2.11).

CONCLUSIONS

Asian Indians with mild dysglycemia have reduced β-cell function, regardless of age, adiposity, insulin sensitivity, or family history. Strategies in diabetes prevention should minimize loss of β-cell function.

Association of β-cell function and insulin sensitivity with fasting and 2-h plasma glucose in a large Chinese population

AIM

Our aim was to provide a quantitative analysis of the changes in the principal determinants of insulin sensitivity and secretion in relation to fasting plasma glucose (FPG) or 2-h plasma glucose (2h PG) in a Chinese population with a wide range of glucose tolerance.

METHODS

A total of 5728 adults spanning the entire range of glucose tolerance were included. Insulin sensitivity was measured by Matsuda insulin sensitivity index (ISI(M)) and homeostasis model assessment of 1/homeostasis model assessment of insulin resistance (HOMA-IR). β-Cell function adjusted by insulin sensitivity was assessed from disposition index (DI) at early-phase DI(30) and total DI(120). The exponential curve was established as the best fit for the relationship between insulin sensitivity or β-cell function and FPG or 2h PG.

RESULTS

Relative to the trend classified as increasing 2h PG, hepatic insulin sensitivity and insulin secretion showed a decreasing trend to a substantial degree as FPG increased. A 1 mmol/l increase in FPG and 2h PG concentration was associated with a -22 and -21% decline in ISI(M), -16 and -4% in 1/HOMA-IR, -38 and -35% in DI(30) and -36 and -26% in DI(120). The decay constant of ISI(M) and DI(30) in IFG or ISI(M), 1/HOMA-IR, DI(30) and DI(120) in IGT was lower than that in normal glucose tolerance. Significant interactions between sex and glucose levels determining DI were found.

CONCLUSIONS

We conclude that impairment of insulin sensitivity and insulin secretion contributes to both FPG or 2h PG hyperglycaemia in a Chinese population, but that the decline in insulin secretion is more pronounced with increasing fasting than 2h PG.

Impaired early- but not late-phase insulin secretion in subjects with impaired fasting glucose

Subjects with impaired fasting glucose (IFG) are at increased risk for type 2 diabetes. We recently demonstrated that IFG subjects have increased hepatic insulin resistance with normal insulin sensitivity in skeletal muscle. In this study, we quantitated the insulin secretion rate from deconvolution analysis of the plasma C-peptide concentration during an oral glucose tolerance test (OGTT) and compared the results in IFG subjects with those in subjects with impaired glucose tolerance (IGT) and normal glucose tolerance (NGT). One hundred and one NGT subjects, 64 subjects with isolated IGT, 24 subjects with isolated IFG, and 48 subjects with combined (IFG + IGT) glucose intolerance (CGI) received an OGTT. Plasma glucose, insulin, and C-peptide concentrations were measured before and every 15 min after glucose ingestion. Insulin secretion rate (ISR) was determined by deconvolution of plasma C-peptide concentration. Inverse of the Matsuda index of whole body insulin sensitivity was used as a measure of insulin resistance; 56 subjects also received a euglycemic hyperinsulinemic clamp. The insulin secretion/insulin resistance (disposition) index was calculated as the ratio between incremental area under the ISR curve (∆ISR[AUC]) to incremental area under the glucose curve (∆G[AUC]) factored by the severity of insulin resistance (measured by Matsuda index during OGTT or glucose disposal during insulin clamp). Compared to NGT, the insulin secretion/insulin resistance index during first 30 min of OGTT was reduced by 47, 49, and 74% in IFG, IGT, and CGI, respectively (all < 0.0001). The insulin secretion/insulin resistance index during the second hour (60-120 min) of the OGTT in subjects with IFG was similar to that in NGT (0.79 ± 0.6 vs. 0.72 ± 0.5, respectively, P = NS), but was profoundly reduced in subjects with IGT and CGI (0.31 ± 0.2 and 0.19 ± 0.11, respectively; P < 0.0001 vs. both NGT and IFG). Early-phase insulin secretion is impaired in both IFG and IGT, while the late-phase insulin secretion is impaired only in subjects with IGT.

Efficacy of primary prevention interventions when fasting and postglucose dysglycemia coexist: analysis of the Indian Diabetes Prevention Programmes (IDPP-1 and IDPP-2)

OBJECTIVE

Impaired glucose tolerance (IGT) and impaired fasting glucose (IFG) have different pathophysiological abnormalities, and their combination may influence the effectiveness of the primary prevention tools. The hypothesis was tested in this analysis, which was done in a pooled sample of two Indian Diabetes Prevention Programmes (IDPP-1 and IDPP-2).

RESEARCH DESIGN AND METHODS

Researchers analyzed and followed up on the details of 845 of the 869 IGT subjects in the two studies for 3 years. Incidence of diabetes and reversal to normoglycemia (normal glucose tolerance [NGT]) were assessed in group 1 with baseline isolated IGT (iIGT) (n = 667) and in group 2 with IGT + IFG (n = 178). The proportion developing diabetes in the groups were analyzed in the control arm with standard advice (IDPP-1) (n = 125), lifestyle modification (LSM) (297 from both), metformin (n = 125, IDPP-1), and LSM + metformin (n = 121, IDPP-1) and LSM + pioglitazone (n = 298, IDPP-2). Cox regression analysis was used to assess the influence of IGT + IFG versus iIGT on the effectiveness of the interventions.

RESULTS

Group 2 had a higher proportion developing diabetes in 3 years (56.2 vs. 33.6% in group 1, P = 0.000) and a lower rate of reversal to NGT (18 vs. 32.1%, P = 0.000). Cox regression analysis showed that effectiveness of intervention was not different in the presence of fasting and postglucose glycemia after adjusting for confounding variables.

CONCLUSIONS

The effectiveness of primary prevention strategies appears to be similar in subjects with iIGT or with combined IGT + IFG. However, the possibility remains that a larger study might show that the effectiveness is lower in those with the combined abnormality.

Changes in insulin sensitivity and insulin release in relation to glycemia and glucose tolerance in 6,414 Finnish men

OBJECTIVE

We evaluated insulin sensitivity and insulin secretion across the entire range of fasting (FPG) and 2-h plasma glucose (PG), and we investigated the differences in insulin sensitivity and insulin release in different glucose tolerance categories.

RESEARCH DESIGN AND METHODS

A total of 6,414 Finnish men (aged 57 +/- 7 years, BMI 27.0 +/- 3.9 kg/m2) from our ongoing population-based METSIM (Metabolic Syndrome in Men) study were included. Of these subjects, 2,168 had normal glucose tolerance, 2,859 isolated impaired fasting glucose (IFG), 217 isolated impaired glucose tolerance (IGT), 701 a combination of IFG and IGT, and 469 newly diagnosed type 2 diabetes.

RESULTS

The Matsuda index of insulin sensitivity decreased substantially within the normal range of FPG (-17%) and 2-h PG (-37%) and was approximately -65 and -53% in the diabetic range of FPG and 2-h PG, respectively, compared with the reference range (FPG and 2-h PG <5.0 mmol/l). Early-phase insulin release declined by only approximately -5% within the normal range of FPG and 2-h PG but decreased significantly in the diabetic range of FPG (by 32-70%) and 2-h PG (by 33-51%). Changes in insulin sensitivity and insulin secretion in relation to hyperglycemia were independent of obesity. The predominant feature of isolated IGT was impaired peripheral insulin sensitivity. Isolated IFG was characterized by impaired early and total insulin release.

CONCLUSIONS

Peripheral insulin sensitivity was already decreased substantially at low PG levels within the normoglycemic range, whereas impairment in insulin secretion was observed mainly in the diabetic range of FPG and 2-h PG. Obesity did not affect changes in insulin sensitivity or insulin secretion in relation to hyperglycemia.

Impaired fasting glucose with or without impaired glucose tolerance: progressive or parallel states of prediabetes?

Our objective was to determine whether defects underlying impaired fasting glucose (IFG) are maintained and additive when combined with impaired glucose tolerance (IGT) (representing a progressive form of prediabetes) or are distinct in IFG/IGT (reflecting a parallel form of prediabetes). Volunteers with IFG (n = 10), IFG/IGT (n = 14), or normal glucose tolerance (NGT; n = 15) were matched for demographics and anthropometry. Insulin secretion was assessed using the glucose step-up protocol and insulin action through the use of a two-stage hyperinsulinemic euglycemic clamp with infusion of [6,6-(2)H(2)]glucose. Modeling of insulin secretory parameters revealed similar basal (Phi(b)) but diminished dynamic (Phi(d)) components in both IFG and IFG/IGT (P = 0.05 vs. NGT for both). Basal glucose rate of appearance (R(a)) was higher in IFG compared with NGT (P < 0.01) and also, surprisingly, with IFG/IGT (P < 0.04). Moreover, glucose R(a) suppressed more during the low-dose insulin clamp in IFG (P < 0.01 vs. NGT, P = 0.08 vs. IFG/IGT). Insulin-stimulated glucose uptake [glucose rate of disappearance (R(d))] was similar in IFG, IFG/IGT, and NGT throughout the clamp. We conclude that nuances of beta-cell dysfunction observed in IFG were also noted in IFG/IGT. A trend for additional insulin secretory defects was observed in IFG/IGT, possibly suggesting progression in beta-cell failure in this group. In contrast, basal glucose R(a) and its suppressability with insulin were higher in IFG, but not IFG/IGT, compared with NGT. Together, these data indicate that IFG/IGT may be a distinct prediabetic syndrome rather than progression from IFG.

Impaired fasting glycaemia vs impaired glucose tolerance: similar impairment of pancreatic alpha and beta cell function but differential roles of incretin hormones and insulin action

AIMS/HYPOTHESIS

The impact of strategies for prevention of type 2 diabetes in isolated impaired fasting glycaemia (i-IFG) vs isolated impaired glucose tolerance (i-IGT) may differ depending on the underlying pathophysiology. We examined insulin secretion during OGTTs and IVGTTs, hepatic and peripheral insulin action, and glucagon and incretin hormone secretion in individuals with i-IFG (n = 18), i-IGT (n = 28) and normal glucose tolerance (NGT, n = 20).

METHODS

Glucose tolerance status was confirmed by a repeated OGTT, during which circulating insulin, glucagon, glucose-dependent insulinotrophic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) levels were measured. A euglycaemic-hyperinsulinaemic clamp with [3-3H]glucose preceded by an IVGTT was performed.

RESULTS

Absolute first-phase insulin secretion during IVGTT was decreased in i-IFG (p = 0.026), but not in i-IGT (p = 0.892) compared with NGT. Hepatic insulin sensitivity was normal in i-IFG and i-IGT individuals (p > or = 0.179). Individuals with i-IGT had peripheral insulin resistance (p = 0.003 vs NGT), and consequently the disposition index (DI; insulin secretion x insulin sensitivity) during IVGTT (DI(IVGTT))) was reduced in both i-IFG and i-IGT (p < 0.005 vs NGT). In contrast, the DI during OGTT (DI(OGTT)) was decreased only in i-IGT (p < 0.001), but not in i-IFG (p = 0.143) compared with NGT. Decreased levels of GIP in i-IGT (p = 0.045 vs NGT) vs increased levels of GLP-1 in i-IFG (p = 0.013 vs NGT) during the OGTT may partially explain these discrepancies. Basal and post-load glucagon levels were significantly increased in both i-IFG and i-IGT individuals (p < or = 0.001 vs NGT).

CONCLUSIONS/INTERPRETATION

We propose that differentiated preventive initiatives in prediabetic individuals should be tested, targeting the specific underlying metabolic defects.

Impaired fasting glycaemia vs impaired glucose tolerance: similar impairment of pancreatic alpha and beta cell function but differential roles of incretin hormones and insulin action

AIMS/HYPOTHESIS

The impact of strategies for prevention of type 2 diabetes in isolated impaired fasting glycaemia (i-IFG) vs isolated impaired glucose tolerance (i-IGT) may differ depending on the underlying pathophysiology. We examined insulin secretion during OGTTs and IVGTTs, hepatic and peripheral insulin action, and glucagon and incretin hormone secretion in individuals with i-IFG (n = 18), i-IGT (n = 28) and normal glucose tolerance (NGT, n = 20).

METHODS

Glucose tolerance status was confirmed by a repeated OGTT, during which circulating insulin, glucagon, glucose-dependent insulinotrophic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) levels were measured. A euglycaemic-hyperinsulinaemic clamp with [3-3H]glucose preceded by an IVGTT was performed.

RESULTS

Absolute first-phase insulin secretion during IVGTT was decreased in i-IFG (p = 0.026), but not in i-IGT (p = 0.892) compared with NGT. Hepatic insulin sensitivity was normal in i-IFG and i-IGT individuals (p > or = 0.179). Individuals with i-IGT had peripheral insulin resistance (p = 0.003 vs NGT), and consequently the disposition index (DI; insulin secretion x insulin sensitivity) during IVGTT (DI(IVGTT))) was reduced in both i-IFG and i-IGT (p < 0.005 vs NGT). In contrast, the DI during OGTT (DI(OGTT)) was decreased only in i-IGT (p < 0.001), but not in i-IFG (p = 0.143) compared with NGT. Decreased levels of GIP in i-IGT (p = 0.045 vs NGT) vs increased levels of GLP-1 in i-IFG (p = 0.013 vs NGT) during the OGTT may partially explain these discrepancies. Basal and post-load glucagon levels were significantly increased in both i-IFG and i-IGT individuals (p < or = 0.001 vs NGT).

CONCLUSIONS/INTERPRETATION

We propose that differentiated preventive initiatives in prediabetic individuals should be tested, targeting the specific underlying metabolic defects.

Isolated impaired fasting glucose and peripheral insulin sensitivity: not a simple relationship

OBJECTIVE

In a recent consensus statement, the American Diabetes Association (ADA) concluded that individuals with impaired fasting glucose (IFG) have "normal muscle insulin sensitivity." To subject this conclusion to further validation, we evaluated the relationship between glucose tolerance categories and peripheral insulin sensitivity in a large nondiabetic population.

RESEARCH DESIGN AND METHODS

Insulin sensitivity was directly quantified by determining the steady-state plasma glucose (SSPG) concentration during an insulin suppression test in 446 nondiabetic individuals divided into four groups: normal glucose tolerance (NGT, n = 318), isolated IFG (n = 63), isolated impaired glucose tolerance (IGT, n = 33), and combined IFG and IGT (IFG/IGT, n = 32).

RESULTS

Insulin sensitivity was significantly different in all three groups with pre-diabetes (IFG, IGT, IFG/IGT) as compared with NGT (P < 0.05). Using tertiles of SSPG concentration in the NGT group as operational definitions of insulin resistance (highest tertile) and insulin sensitivity (lowest tertile), there was considerable heterogeneity within the pre-diabetic groups. Thus, 57% of IFG individuals were insulin resistant, and 13% were insulin sensitive. The IFG/IGT group was most homogeneous, with 94% classified as insulin resistant and only 3% as insulin sensitive.

CONCLUSIONS

Peripheral insulin sensitivity varies considerably in nondiabetic individuals, with IFG individuals showing the most heterogeneity within the pre-diabetes group. We believe that this heterogeneity in insulin sensitivity, and the relatively few patients in whom insulin sensitivity has been measured directly in the past, explain the discrepancy between our findings and those of the recent ADA consensus statement.

Differences in insulin sensitivity and secretory capacity based on OGTT in subjects with impaired glucose regulation

BACKGROUND

This study examined whether defects in insulin secretion contribute to the development and progression of type 2 diabetes mellitus (T2DM).

METHODS

Plasma insulin and glucose were measured after a glucose tolerance test to calculate the insulinogenic index (IGI) and the HOMA-IR Homeostasis model assessment of insulin resistance in subjects with normal glucose tolerance (NGT), prediabetes (preDM, n = 49), and T2DM patients with disease duration < 1 year (n = 84), 1 approximately 5 years (n = 45), or > 5 years (n = 37). Plasma proinsulin and adiponectin levels were also measured as a parameter of insulin secretion and resistance.

RESULTS

The mean HOMA-IR increased and the adiponectin levels decreased relative to the deterioration of glucose tolerance in NGT and preDM subjects. However, differences in the HOMA-IR were not related to disease duration in T2DM subjects. The mean IGI was similar in NGT and preDM subjects, but there were significant deteriorations in IGI relative to the duration of diabetes.

CONCLUSIONS

Defects in both insulin sensitivity and insulin secretion contribute to T2DM, but decreased insulin secretion may be more important in the development and progression of T2DM.

High prevalence of glucose intolerance even among young adults in south India

India is experiencing an epidemic of Type 2 diabetes mellitus (DM) in young adults. This study reports the prevalence of glucose intolerance, and insulin profiles, and their relationship to lifestyle factors in 2218 young adults (aged 26-32 years; 997 urban, 1221 rural) in south India. They were drawn from a cohort of 10,691 individuals born during 1969-1973 in Vellore and nearby villages. Family history, socio-economic status, physical activity and tobacco and alcohol use were recorded. Oral glucose tolerance tests were performed for diagnosis (WHO recommendations). Insulin resistance and secretion were derived from plasma insulin concentrations. Median BMI was 20.0kg/m(2). The prevalence of Type 2 DM and impaired glucose tolerance (IGT) was higher in urban than in rural subjects (3.7% versus 2.1%, p=0.02; 18.9% versus 14.3%, p=0.002, respectively), while prevalence of impaired fasting glycaemia (IFG) was similar in urban and rural populations (3.8% versus 3.4%, p=0.04). Type 2 DM, IGT, IFG or higher insulin resistance and increment were associated with higher socio-economic status (more household possessions) and higher percentage body fat, body mass index and waist/hip ratio. Insulin increment was lower in men with higher alcohol consumption. Our data suggest high levels of glucose intolerance in young rural and urban adults highlighting an urgent need for preventive action to avert a public health catastrophe in India.

Impaired Glucose Tolerance and Impaired Fasting Glucose Share Similar Underlying Pathophysiologies

Both impaired glucose tolerance (IGT) and impaired fasting glucose (IFG) are pre-diabetic states. IGT was defined as having normal fasting plasma glucose (< 6.1 mmol/l) and abnormal 2-hr post-challenge plasma glucose. IFG was defined as having abnormal fasting plasma and normal 2-hr post-challenge plasma glucose (< 7.8 mmol/l). To explore whether these two abnormalities share similar underlying pathophysiologies, we evaluated risk factors of IGT and IFT using the models of factor analysis. The present study included 107 subjects with IGT and 52 with IFG. An oral glucose tolerance test and insulin suppression test, which could quantify insulin resistance, were performed on separate days. The risk factors include waist-to-hip ratio (WHR), triglycerides, high-density lipoprotein (HDL)-cholesterol, blood pressure, and fasting plasma glucose, which are associated with metabolic syndrome and insulin resistance. Factor analysis is a commonly used statistical method that could reduce a large number of risk factors into smaller numbers of groups, also called dimension. Accordingly, the complicated data could be interpreted more easily, since the related risk factors are grouped in one dimension. The results showed that the risk factors of IGT and IFG have similar grouping patterns. Triglyceride, insulin resistance, and HDL-cholesterol were grouped in one dimension (the lipid dimension), while WHR, mean blood pressure and fasting plasma glucose were grouped in another dimension (the metabolic dimension). In conclusion, except for WHR, the grouping patterns of the components in both IGT and IFG were nearly identical. These results suggest that IGT and IFG may share similar pathophysiologies.

Different mechanisms for impaired fasting glucose and impaired postprandial glucose tolerance in humans

OBJECTIVE

To compare the pathophysiology of impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) in a more comprehensive and standardized fashion than has hitherto been done.

RESEARCH DESIGN AND METHODS

We studied 21 individuals with isolated IFG (IFG/normal glucose tolerance [NGT]), 61 individuals with isolated IGT (normal fasting glucose [NFG]/IGT), and 240 healthy control subjects (NFG/NGT) by hyperglycemic clamps to determine first- and second-phase insulin release and insulin sensitivity. Homeostasis model assessment (HOMA) indexes of beta-cell function (HOMA-%B) and insulin resistance (HOMA-IR) were calculated from fasting plasma insulin and glucose concentrations.

RESULTS

Compared with NFG/NGT, IFG/NGT had similar fasting insulin concentrations despite hyperglycemia; therefore, HOMA-IR was increased approximately 30% (P < 0.05), but clamp-determined insulin sensitivity was normal (P > 0.8). HOMA-%B and first-phase insulin responses were reduced approximately 35% (P < 0.002) and approximately 30% (P < 0.02), respectively, but second-phase insulin responses were normal (P > 0.5). NFG/IGT had normal HOMA-IR but approximately 15% decreased clamp-determined insulin sensitivity (P < 0.03). Furthermore, HOMA-%B was normal but both first-phase (P < 0.0003) and second-phase (P < 0.0001) insulin responses were reduced approximately 30%. IFG/NGT differed from NFG/IGT by having approximately 40% lower HOMA-%B (P < 0.012) and approximately 50% greater second-phase insulin responses (P < 0.005).

CONCLUSIONS

Since first-phase insulin responses were similarly reduced in IFG/NGT and NFG/IGT, we conclude that IFG is due to impaired basal insulin secretion and preferential resistance of glucose production to suppression by insulin, as reflected by fasting hyperglycemia despite normal plasma insulin concentrations and increased HOMA-IR, whereas IGT mainly results from reduced second-phase insulin release and peripheral insulin resistance, as reflected by reduced clamp-determined insulin sensitivity.

Contributions of beta-cell dysfunction and insulin resistance to the pathogenesis of impaired glucose tolerance and impaired fasting glucose

Impaired glucose tolerance (IGT) and impaired fasting glucose (IFG) are intermediate states in glucose metabolism that exist between normal glucose tolerance and overt diabetes. Epidemiological studies demonstrate that the two categories describe distinct populations with only partial overlap, suggesting that different metabolic abnormalities characterize IGT and IFG. Insulin resistance and impaired beta-cell function, the primary defects observed in type 2 diabetes, both can be detected in subjects with IGT and IFG. However, clinical studies suggest that the site of insulin resistance varies between the two disorders. While subjects with IGT have marked muscle insulin resistance with only mild hepatic insulin resistance, subjects with IFG have severe hepatic insulin resistance with normal or near-normal muscle insulin sensitivity. Both IFG and IGT are characterized by a reduction in early-phase insulin secretion, while subjects with IGT also have impaired late-phase insulin secretion. The distinct metabolic features present in subjects with IFG and IGT may require different therapeutic interventions to prevent their progression to type 2 diabetes.