Claimed effects, outcome variables and methods of measurement for health claims proposed under regulation (EC) 1924/2006 and related to cognitive function in adults

Some food/food components have been the object of request of authorization to the use of health claims related to cognitive function in adults and compliant with the Regulation (EC) 1924/2006. Most of the requests have received a negative opinion by the European Food Safety Authority (EFSA) also because of the choice of not appropriate outcome variables (OVs) and methods of measurement (MMs) selected in the trials used to substantiate the claim. This manuscript referes to the collection, collation and critical analysis of OVs and MMs related to cognitive function in adults. OVs and MMs were collected from the EFSA Guidance document and the applications for authorization of health claims pursuant to the Articles 13(5). The critical analysis of OVs and MMs, performed by a literature review, was aimed at defining their appropriateness in the context of a specific claimed effect. The results highlight the importance of an adequate choice of OVs and MMs for an effective substantiation of the claims related to cognitive functioning. The information provided in this document may serve to EFSA for updating the guidance on the scientific requirements for health claims related to cognitive functions, but also for a better design of randomized controlled trials aimed at substantiating such health claims.

Claimed effects, outcome variables and methods of measurement for health claims proposed under European Community Regulation 1924/2006 in the framework of protection against oxidative damage and cardiovascular health

BACKGROUND AND AIMS

The high number of negative opinions from the European Food Safety Authority (EFSA) to the requests for authorization of health claims is largely due to the design of human intervention studies, including the inappropriate choice of outcome variables (OVs) and of their methods of measurement (MMs). The present manuscript reports the results of an investigation aimed to collect, collate and critically analyse the information in relation to claimed effects, OVs and MMs, in the context of protection against oxidative damage and cardiovascular health compliant with Regulation 1924/2006.

METHODS AND RESULTS

Claimed effects, OVs and the related MMs were collected from EFSA Guidance documents and applications for authorization of health claims under Articles 13.5 and 14. The OVs and their MMs were evaluated only if the claimed effect was sufficiently defined and was considered beneficial by EFSA. The collection, collation and critical analysis of the relevant scientific literature consisted in the definition of the keywords, the PubMed search strategies and the creation of databases of references. The critical analysis of the OVs and their MMs was performed on the basis of the literature review and was aimed at defining the appropriateness of OVs and MMs in the context of the specific claimed effects.

CONCLUSIONS

The information provided in this document could serve to EFSA for the development of further guidance on the scientific requirements for health claims, as well as to the stakeholders for the proper design of human intervention studies aimed to substantiate such health claims.

Women show worse control of type 2 diabetes and cardiovascular disease risk factors than men: results from the MIND.IT Study Group of the Italian Society of Diabetology

BACKGROUND AND AIMS

The study explores the degree of control of hyperglycaemia and cardiovascular (CV) disease risk factors in men and women with type 2 diabetes and the impact thereon of obesity, central adiposity, age and use of medications.

METHODS AND RESULTS

A cross-sectional survey was conducted at 10 hospital-based outpatients diabetes clinics. 1297 men and 1168 women with no previous CV events were studied. Women were slightly (only one year) older and more obese than men: average BMI was respectively 30.7 ± 5.7 vs 28.6 ± 4.1 kg/m(2) (p < 0.001), and prevalence of abdominal obesity was 86% vs 44% (p < 0.001). Women smoked less, but had higher HbA1c, LDL cholesterol, non-HDL cholesterol, systolic blood pressure and serum fibrinogen than men. Accordingly optimal targets for HbA1c (<7%), LDL cholesterol (<100 mg/dL), HDL cholesterol (>40 for men, >50 for women, mg/dL), and systolic blood pressure (<130 mmHg) were less frequently achieved by women than men (respectively 33.8% vs 40.2%; 14.6% vs 19.2%; 34.1% vs 44.5%; 68.8% vs 72%; p < 0.05 for all). Findings were confirmed after stratification for waist circumference (< or ≥ 88 cm for women; < or ≥ 102 cm for men), BMI (< or ≥ 25 kg/m(2)) or age (< or ≥ 65 years). As for treatment, women were more likely than men to take insulin, alone or in combination with oral hypoglycaemic drugs, to be under anti-hypertensive treatment, whereas the use of lipid lowering drugs was similar in men and women.

CONCLUSIONS

Control of hyperglycaemia and major CVD risk factors is less satisfactory in women than men. The gender disparities are not fully explained by the higher prevalence of total and central obesity in women; or by a less intensive medical management in women.

Lower endothelial progenitor cell number, family history of cardiovascular disease and reduced HDL-cholesterol levels are associated with shorter leukocyte telomere length in healthy young adults

BACKGROUND AND AIMS

Leukocyte telomere length (LTL) is a novel marker of cardiovascular (CV) risk. The aim of the study was to investigate the major determinants of LTL in a healthy young population at very low CV risk.

METHODS AND RESULTS

LTL was determined in 82 healthy subjects (49M/33F; age37 ± 9yrs), normotensive and not taking any medication with different family history of cardiovascular disease (CVD) (24yes/58no). Fasting blood samples were drawn in all subjects for the determination of lipid profile, high sensitive C-reactive protein, uric acid, Plasminogen Activator Inhibitor-1 (PAI-1), LTL and Endothelial Progenitor Cell (EPC) number. LTL was assessed with a specific real-time PCR reaction in leukocyte DNA samples. LTL resulted inversely correlated with family history of CVD (t = 2.70; p = 0.009), age (r = -0.238; p = 0.032), waist circumference (r = -0.256; p = 0.02), triglycerides (r = -0.218; p = 0.049), PAI-1 (r = -0.288; p = 0.009) and directly correlated with HDL-cholesterol (r = 0.316; p = 0.004) and EPC number (r = 0.358; p = 0.002). At a multivariate analysis, family history of CVD (p = 0.013), EPC count (p = 0.003), and HDL-cholesterol (p = 0.017) were independently associated with LTL (r = 0.62).

CONCLUSION

LTL is independently associated to CV risk factors also in healthy young adults.

Multivariate prediction of subcutaneous glucose concentration in type 1 diabetes patients based on support vector regression

Data-driven techniques have recently drawn significant interest in the predictive modeling of subcutaneous (s.c.) glucose concentration in type 1 diabetes. In this study, the s.c. glucose prediction is treated as a multivariate regression problem, which is addressed using support vector regression (SVR). The proposed method is based on variables concerning: (i) the s.c. glucose profile, (ii) the plasma insulin concentration, (iii) the appearance of meal-derived glucose in the systemic circulation, and (iv) the energy expenditure during physical activities. Six cases corresponding to different combinations of the aforementioned variables are used to investigate the influence of the input on the daily glucose prediction. The proposed method is evaluated using a dataset of 27 patients in free-living conditions. 10-fold cross validation is applied to each dataset individually to both optimize and test the SVR model. In the case where all the input variables are considered, the average prediction errors are 5.21, 6.03, 7.14 and 7.62 mg/dl for 15, 30, 60 and 120 min prediction horizons, respectively. The results clearly indicate that the availability of multivariable data and their effective combination can significantly increase the accuracy of both short-term and long-term predictions.

Macrophage polarization: the answer to the diet/inflammation conundrum?

Macrophages, a heterogeneous and ubiquitous cell population representing up to 15% of the cellular content of different types of tissue, are the principal cell mediators in response to pathogens, inflammation process, tissue homeostasis and repair and play a pivotal role in atherosclerosis and insulin resistance because of their capacity to be the major source of inflammatory cytokines, which can function through paracrine and endocrine mechanisms. Recently, differently activated macrophage populations have been described, depending on a large variety of microenvironmental signals, and it is now recognized that their activation plays a crucial role in the development and progression of atherosclerosis. There is good evidence of the ability of conjugated linoleic acids and polyphenolic compounds to modulate inflammation in experimental models involving macrophages. This observation leaves room to the intriguing hypothesis that macrophage polarization could represent one of the unifying mechanisms through which specific food components can exert anti-inflammatory effects in humans, contributing to the prevention of chronic diseases strongly linked to inflammation, such as atherosclerosis. Future studies should be addressed to substantiate this hypothesis, investigating whether or not physiological concentrations of food-derived metabolites can perturb macrophage activation in vitro. On the in vivo side, the evaluation of macrophage populations in tissues, however complex, should be included among the analyses performed in observational and intervention studies, in order to understand if macrophage activation is involved in the anti-inflammatory activity of a specific dietary regimen.

Effects of chronic elevation of atrial natriuretic peptide and free fatty acid levels in the induction of type 2 diabetes mellitus and insulin resistance in patients with mitral valve disease

BACKGROUND AND AIMS

The relationship between atrial natriuretic peptide (ANP), increased free fatty acid (FFA) and insulin resistance in patients with mitral valve disease (MVD), a group characterised by elevated atrial pressure and increased ANP levels, is not defined. The present study was performed to evaluate, in MVD patients, the relationship between increased ANP and FFA levels and insulin resistance and the role of mitral valve replacement/repair in ameliorating these metabolic alterations. Conversely, coronary heart disease (CHD) patients were evaluated before and after coronary artery bypass grafting (CABG), since they are known to be insulin resistant in the presence of chronic FFA increase.

METHODS AND RESULTS

Fifty MVD patients and 55 CHD patients were studied before and 2 months after surgery and compared with 166 normal subjects. Before surgery, 56% of MVD patients had impaired glucose tolerance or newly diagnosed type 2 diabetes after a standard oral glucose load and this percentage decreased to 46% after surgery. In CHD, impaired glucose tolerance (IGT) or newly diagnosed type 2 diabetic patients were 67% of patients before and after CABG. In MVD, left atrial (LA) volume, ANP, FFA incremental area and insulin levels were higher and Insulin Sensitivity (IS) index significantly reduced while after surgery, LA volume, ANP and FFA significantly decreased and IS index significantly improved. In CHD, insulin resistance and hyperinsulinaemia were present both before and after surgery with increased tumour necrosis factor (TNF)-α and interleukin (IL)-6 levels.

CONCLUSION

In MVD, a higher degree of abnormal glucose tolerance and insulin resistance are associated to increased levels of ANP and FFA, while these metabolic alterations are improved by mitral valve replacement/repair surgery. Clinical Trial.gov registration number NCT 00520962.

Food selection based on high total antioxidant capacity improves endothelial function in a low cardiovascular risk population

BACKGROUND AND AIMS

Oxidative stress has been advocated as a major cause for cardiovascular disease (CVD), and low plasma antioxidant concentrations are associated with endothelial dysfunction, the first step towards atherosclerosis. However, although the antioxidant content in fruits and vegetables may explain at least in part their protective effect against CVD, supplementation with antioxidant vitamins fails to improve endothelial function and reduce CVD risk. The aim of this study was to investigate the impact of a diet rich in antioxidants on endothelial function measured by flow-mediated dilatation (FMD) in volunteers at low cardiovascular risk.

METHODS AND RESULTS

In a crossover trial, 24 subjects (13 women, mean age 61 ± 3 years), received, in a randomised order, a 14-day high (HT) and a 14-day low (LT) antioxidant diets, with a 2-week wash-out (WO) in between. Both diets were comparable in daily portions of fruits and vegetables, and in alcohol, fibre and macronutrient intake, but differed in their total antioxidant capacity. Before and after each diet, anthropometrics, blood pressure, fasting plasma glucose, lipid profile, hepatic enzymes, circulating antioxidant concentrations, high sensitivity C-reactive protein (hs-CRP) and FMD were assessed. FMD increased significantly during the HT diet compared to the LT (p < 0.000). FMD values were 2.3% higher after HT compared with LT (p < 0.001) after adjustment for age, gender and diet order. α-tocopherol increased significantly (p < 0.05) and hs-CRP and of γ-glutamyltranspeptidase decreased significantly (p < 0.05 and p < 0.01, respectively) during the HT diet, compared with the LT diet.

CONCLUSIONS

A short-term HT diet improves endothelial function in volunteers at low cardiovascular risk, which may further reduce their risk of CVD.

[Chronic heart failure and cachexia: role of endocrine system]

Chronic heart failure (CHF) is a major health problem that carries a devastating prognosis. The prognosis worsens considerably once cardiac cachexia has been diagnosed. Neurohormonal, metabolic, hemodynamic and immunological alterations are involved in the initiation and progression of cardiac cachexia. Cachexia is characterized by a hypothalamic inappropriate response to the mechanisms controlling energy homeostasis. Levels of the anorexigenic hormone leptin are decreased whereas the orexigenic gherlin hormone levels are normal or elevated. Nevertheless, energy intake is not increased as expected due to a persistent activation of the proopiomelanocortin (POMC) system (anorexigenic) paralleled by a decreased activity of the neuropeptide Y (NPY, orexigenic) neurons. Cachexia is also characterized by an imbalance in anabolic (impairment in the growth hormone/insulin-like growth factor-I axis, insulin resistance) and catabolic (increased levels of catecholamines, increased cortisol/dehydroepiandrosterone ratio and activation of proinflammatory cytokines such as tumor necrosis factor-alpha, interleuchin-6, interleuchin-1') at the basis of the wasting process. This review discusses the complex role of the endocrine system in modulating energy balance, appetite and metabolism in patients with chronic heart failure. A joint multidisciplinary effort of the cardiologists, immunologists and endocrinologists might be useful to identify the precise mechanisms involved in the neuroendocrine alteration and to develop therapeutic strategies able to improve the prognosis of CHF patients.

Reduced circulating endothelial progenitor cell number in healthy young adult hyperinsulinemic men

BACKGROUND AND AIMS

The number of Endothelial Progenitor Cells (EPCs) is considered a novel marker of cardiovascular (CV) disease. It is not clear which are the main determinants of EPC number in apparently healthy subjects in the absence of overt clinical CV or metabolic abnormalities. We evaluated the main clinical determinants of EPC levels in a population of healthy subjects with normal glucose tolerance.

METHODS AND RESULTS

EPC number was determined in 122 healthy subjects (73M/49F;36.6 ± 8yrs). Blood samples were collected to test biochemical variables. OGTT was performed and insulin resistance/compensatory hyperinsulinemia was defined according to fasting plasma insulin (FPI) levels. EPCs were identified as cells co-expressing CD133/CD34/KDR antigens by flow-cytometry. CD133(+)/KDR(+) count inversely correlated with BMI (rho=-0.18;p < 0.05), waist circumference (-0.2;<0.05), diastolic (-0.23;<0.01) and systolic blood pressure (-0.21;<0.05), uric acid (-0.24;<0.005), PAI-1 (-0.197; <0.05) and FPI (-0.2;<0.05) and directly correlated with HDL cholesterol (0.182;<0.05). CD34(+)/CD133(+)/KDR(+) count inversely correlated with uric acid (-0.28;<0.005) and FPI (-0.2;<0.05). EPC number was lower in males (p < 0.05) and gender was the only independent predictor of EPC count (p < 0.05). By dividing the population in four subgroups based on gender and insulin resistance, CD133(+)/KDR(+) levels were lower in insulin resistant compared to insulin sensitive males (p < 0.05) with no differences in females.

CONCLUSION

The male gender is an independent predictor of low EPC levels in healthy subjects. This might contribute to explaining the higher CV risk in males compared to pre-menopausal age-matched females. In this study a reduced EPC number seems to be associated with insulin resistance in male subjects.

Intake of the plant lignans matairesinol, secoisolariciresinol, pinoresinol, and lariciresinol in relation to vascular inflammation and endothelial dysfunction in middle age-elderly men and post-menopausal women living in Northern Italy

BACKGROUND AND AIMS

It has been suggested that lignan intake may decrease the risk for cardiovascular disease (CVD) by modifying traditional risk factors as well as aortic stiffness. However, the role of dietary lignans on the vascular system is largely unknown. The objective was to investigate whether dietary intake of plant lignans in a free-living population was associated with markers of vascular inflammation and function.

METHODS AND RESULTS

We performed a cross-sectional study in 242 (151 males) men and post-menopausal women. Anthropometric characteristics and lignan intake were evaluated. Soluble intercellular adhesion molecule-1 (sICAM-1), insulin, high-sensitive C-reactive protein, glucose, total cholesterol, HDL-cholesterol and triacylglycerols were measured in fasting blood samples. Brachial flow-mediated dilation (FMD) measurements were available for 101 subjects (56 males). Median (interquartile range) daily intake of matairesinol (MAT), secoisolariciresinol (SECO), pinoresinol (PINO), lariciresinol (LARI), and total lignans was 20.9 microg (17.4), 335.3 microg (289.1), 96.7 microg (91.1), 175.7 microg (135.8), and 665.5 microg (413.7), respectively, as assessed by 3-day weighed food record. Plasma concentrations of sICAM-1 (whole sample) significantly decreased (mean (95%CI) = 358 microg/L (320-401), 276 microg/L (252-303), 298 microg/L (271-326), and 269 microg/L (239-303), P per trend 0.013) and FMD values (FMD sub-group) significantly increased (4.1% (2.2-6.0), 5.7% (4.3-7.2), 6.4% (4.9-7.8), and 8.1% (6.3-10.0), P per trend 0.016) across quartiles of energy-adjusted MAT intake, even after adjustment for relevant clinical and dietary variables. Intake of SECO was also inversely related to plasma sICAM-1 (P per trend 0.018), but not to FMD values. No relationship between intake of PINO, LARI or total lignans and either sICAM-1 or FMD values was observed.

CONCLUSIONS

Higher MAT intakes in the context of a typical Northern Italian diet are associated to lower vascular inflammation and endothelial dysfunction, which could have some implications in CVD prevention.

The clinical reality of guidelines for primary prevention of cardiovascular disease in type 2 diabetes in Italy

INTRODUCTION AND AIM

Guidelines for cardiovascular prevention in diabetes have been issued by the national and international scientific societies. No audit as ever been performed to evaluate the implementation of these documents in clinical practice in Italy. The study evaluates the prevalence, treatment, and control of major cardiovascular risk factors in type 2 diabetic patients, to assess the clinical practice of primary cardiovascular prevention in type 2 diabetes.

PATIENTS AND METHODS

Two thousand four hundred and sixty-five men and women with type 2 diabetes, aged 50-75 and free of cardiovascular events were recruited on a consecutive basis at 10 hospital based outpatients diabetes clinics. Clinical variables were measured by standard protocol. Biochemical parameters were evaluated at each centre. The laboratories were monitored by an external quality control assessment in order to reach and maintain a standard of quality and traceability among the participating centres.

RESULTS

A minority of patients (5%) met the recommended targets for LDL cholesterol, blood pressure, glycated haemoglobin and smoking habits, whereas the vast majority (66%) had unsatisfactory control of three or more of the above. Achievement of desirable control of risk factors differed according to gender and known diabetes duration. Lipid lowering and, to a lesser extent, antihypertensive medications were under-used and their titration insufficiently target-driven. Prophylactic use of antiplatelet agents was scarce, only one out of five patients was treated independent of absolute cardiovascular risk.

CONCLUSION

In clinical practice there is poor adherence to national and international guidelines for primary cardiovascular prevention in type 2 diabetes in Italy. The study underlines the great potential for prevention, particularly in women and in high-risk patients.

Prevalence of elevated liver enzymes in Type 2 diabetes mellitus and its association with the metabolic syndrome

The occurrence of liver disease and raised liver enzymes is common in Type 2 diabetes, and may be multifactorial in origin. Very few studies are available on the exact prevalence of the phenomenon, however. We carried out an observational point-prevalence study of elevated liver enzymes in eight hospital-based Italian diabetes units. Data of 9621 consecutive Type 2 diabetes patients (males, 52.4%; median age, 65 yr) were analyzed, and alanine and aspartate aminotransferase (ALT, AST) and gamma-glutamyltransferase (GGT) levels were related to body mass index (BMI), metabolic control and the presence of the metabolic syndrome. ALT, AST, and GGT levels exceeding the upper limit of normal were present in 16.0%, 8.8%, 23.1%, respectively, the prevalence being higher in males, increasing with obesity class and poor metabolic control, and decreasing with age. Elevated enzymes were systematically associated with most parameters of the metabolic syndrome. After correction for age, gender, BMI, and differences across centers, elevated triglyceride levels/fibrate treatment [odds ratio (OR), 1.57; 95% confidence interval (CI), 1.34- 1.84] and an enlarged waist circumference (OR, 1.47; 95% CI, 1.17-1.85) were the only parameters independently associated with high ALT. In a separate analysis, the presence of metabolic syndrome (Adult Treatment Panel III criteria) was highly predictive of raised liver enzymes. After exclusion of hepatitis B and C positive cases, tested in 2 centers, the prevalence of raised enzymes decreased by approximately 4%, but the association with the metabolic syndrome did not change significantly. In conclusion, the high prevalence of elevated liver enzymes in Type 2 diabetes is in keeping with the well-demonstrated risk of progressive liver disease. A large amount of diabetes patients may require a thorough clinical, laboratory and histological investigation.

Dietary habits in type II diabetes mellitus: how is adherence to dietary recommendations?

OBJECTIVE

To clarify adherence of type II diabetic patients to dietary recommendations.

SUBJECTS AND METHODS

The dietary habits of a group of 540 patients, with type II diabetes (male 322/female 218, mean age 61+/-5 years, body mass index (BMI) 29.7+/-5.2 kg/m(2); mean+/-s.d.) referring to six Italian diabetes centres were evaluated by means of a 3-day diet record (2 workdays, 1 holiday). Diet records were analysed according to Italian food composition tables and compared with the dietary recommendations of the Diabetes and Nutrition Study Group of the European Association for the study of Diabetes.

RESULTS

Calorie intake was 1725+/-497 kcal (1800 for men, 1610 for women). Mean intake for each nutrient was close to the recommended amount, except for fibre (12/1000 vs 20 g/1000 kcal). Calculating the percentage of patients who complied with each recommendation, the intakes of saturated fat and fibre least reflected the dietary target: in 43% of patients saturated fat was >10% of total calories, in only 6% was fibre intake > or =20 g/1000 kcal (considered ideal), and in 25% it was > or =15 g/1000 kcal (acceptable).

CONCLUSIONS

These results indicate that compliance to dietary recommendations is not completely satisfactory, even in Italy. Calorie intake is a bit elevated, given the high BMI of our diabetic population. As to dietary composition, there are two crucial issues: the high intake of saturated fat and--most importantly--the low intake of fibre. All strategies aiming to a proper implementation of guidelines should take these results into due account.

ADMA is independently related to flow-mediated vasodilation in subjects at low cardiovascular risk

BACKGROUND

Increased plasma concentrations of asymmetric dimethylarginine (ADMA) contribute to impair endothelial function in patients with established cardiovascular disease (CVD) and/or individuals with clinical syndromes known to increase CVD. However, the impact of ADMA on endothelial function in apparently healthy individuals has not been determined.

MATERIALS AND METHODS

To address this issue, we measured endothelial-dependent vasodilatation in response to forearm ischaemia (flow-mediated vasodilatation, FMD) in 111 non-smoking, healthy volunteers with low CVD risk by the Framingham risk equation. Measurements were also made of multiple anthropometric, metabolic, and dynamic variables related to FMD. l-arginine and its methylated derivates (ADMA and SDMA) were quantified by high-liquid pressure chromatography.

RESULTS

After adjustment by gender, lower values for FMD were significantly associated with increases in plasma ADMA concentrations (anova linear trend by FMD tertiles, P < 0.05) as well as in brachial artery diameter (partial r = -0.352, P = 0.001), body mass index (-0.337, P = 0.001), fasting insulin (-0.368, P < 0.001) and high-sensitivity C-reactive protein (-0.283, P = 0.007) plasma concentrations, and with decreased HDL cholesterol (0.233, P = 0.026). Multiple linear regression analysis indicated that the only statistically significant predictors of FMD were brachial artery diameter (P < 0.001), ADMA (P < 0.05) and fasting plasma insulin (P < 0.001) concentrations.

CONCLUSIONS

In conclusion, a significant relationship between increases in plasma ADMA concentration and lower values of FMD is not limited to patients with clinical syndromes related to CVD, but can also be seen in healthy subjects at low global CVD risk.

The total antioxidant capacity of the diet is an independent predictor of plasma beta-carotene

OBJECTIVE

To investigate the contribution of the total antioxidant capacity (TAC) of the diet to plasma concentrations of beta-carotene.

DESIGN

Cross-sectional study.

SETTING

Department of Public Health and Department of Internal Medicine and Biomedical Sciences, University of Parma.

SUBJECTS

A total of 247 apparently healthy adult men (n=140) and women (n=107).

METHODS

A medical history, a physical exam including height, weight, waist circumference and blood pressure measurements, a fasting blood draw, an oral glucose tolerance test and a 3-day food record.

RESULTS

We observe a negative trend across quartiles of plasma beta-carotene for most biological variables clustering in the insulin resistance syndrome, as well as for traditional and new risk factors for type II diabetes and cardiovascular disease (CVD), including C-reactive protein and gamma-glutamyltranspeptidase (P<0.05). Regarding dietary characteristics, energy-adjusted intake of fat, fiber, fruits, vegetables, beta-carotene, vitamin C, vitamin E and dietary TAC significantly increased with increasing plasma beta-carotene (P<0.05), whereas alcohol intake decreased (P=0.013). Adjusted geometric means (95% confidence interval) of plasma beta-carotene significantly increased across quartiles of dietary TAC, even when single dietary antioxidants were considered in the model (QI=0.087 mg/dl (0.073-0.102); QII=0.087 mg/dl (0.075-0.103); QIII=0.114 mg/dl (0.098-0.132) and QIV=0.110 mg/dl (0.093-0.130); P for linear trend=0.026). When the population was divided on the basis of alcohol consumption, this trend was also observed in subjects drinking <20 g alcohol/day (P=0.034), but not in those with higher alcohol intake (P=0.448).

CONCLUSIONS

Dietary TAC is an independent predictor of plasma beta-carotene, especially in moderate alcohol drinkers. This may explain, at least in part, the inverse relationship observed between plasma beta-carotene and risk of chronic diseases associated to high levels of oxidative stress (i.e., diabetes and CVD), as well as the failure of beta-carotene supplements alone in reducing such risk.

What is the contribution of differences in three measures of tumor necrosis factor-alpha activity to insulin resistance in healthy volunteers?

To address the potential role that tumor necrosis factor-alpha (TNF-alpha) might play in modulation of insulin resistance in healthy, nondiabetic individuals, we compared plasma TNF-alpha and soluble TNF-alpha receptor 2 (sTNF-R2) concentrations, as well as TNF-alpha polymorphisms, in 94 healthy individuals, stratified into insulin-resistant (IR) and insulin-sensitive (IS) groups based on their plasma insulin concentrations 120 minutes after oral glucose on 2 occasions (1993 and 2000). The IR group (n = 50; 29 men and 21 women) was in the upper quartile and the IS group (n = 44; 24 men and 20 women) in the lowest quartile of the distribution of post-glucose challenge insulin concentrations in a large unselected population (>50 v <23 microU/mL). The IR group had significantly higher values for body mass index, waist-to-hip girth, fasting and post-glucose challenge insulin concentrations, and fasting triglyceride concentrations, and lower high-density lipoprotein cholesterol concentrations as compared to the IS group. Despite the fact that they were relatively more obese, and insulin-resistant, plasma concentrations of TNF-alpha were similar in the IR (1.6 +/- 0.6 pg/mL) and IS (1.7 +/- 0.6 pg/mL) groups, as were the concentrations (5.4 +/- 1.4 v 5.8 +/- 2.0 pg/mL) of sTNF-R2. Furthermore, TNF-alpha polymorphisms (detected by polymerase chain reaction [PCR]) were similar in the 2 groups, with essentially identical allelic frequencies of the 238 (10.3% v 9.4%) and 308 polymorphisms (17.9% v 18.7%). In conclusion, plasma TNF-alpha and sTNF-R2 concentrations, as well as TNF-alpha gene polymorphisms, were not different in healthy volunteers stratified into IR and IS groups on the basis of their plasma insulin response to an oral glucose challenge. Given these data, it does not appear that differences in TNF-alpha activity contribute to the marked variations in insulin action that occur in healthy individuals.

Plasma nitric oxide concentrations are elevated in insulin-resistant healthy subjects

The goal of this study was to compare plasma nitric oxide (NO) concentrations in healthy subjects, defined as either insulin-resistant or insulin-sensitive on the basis of the plasma insulin response to a 75-g oral glucose challenge. For this purpose, 404 healthy subjects were divided into quartiles on the basis of the plasma insulin response to glucose, and 49 individuals were selected from the quartile with the lowest insulin response and 49 from the quartile with the highest insulin response. The two groups of 49 each were selected to be essentially identical in terms of age, gender distribution, body mass index (BMI), and waist to hip ratio (WHR). The quartile with the greatest insulin response also had a significantly higher plasma glucose response to oral glucose, faster heart rate, higher blood pressure, and the combination of higher triglyceride and lower high-density lipoprotein (HDL) cholesterol concentrations. In addition to the latter changes, previously shown to be associated with hyperinsulinemia, NO concentrations were also higher in the hyperinsulinemic group. It is speculated that this increase in the NO concentration in hyperinsulinemic and presumably insulin-resistant, subjects represents a compensatory effort to overcome the untoward effects of insulin resistance and/or hyperinsulinemia.

Alterations in nitric oxide/cyclic-GMP pathway in nondiabetic siblings of patients with type 2 diabetes

In this study, we have compared resistance to insulin-mediated glucose disposal and plasma concentrations of nitric oxide (NO) and cyclic-GMP in healthy volunteers with (n = 35) or without (n = 27) at least one sibling and one parent with type 2 diabetes. The 62 volunteers were further divided into groups of those with normal glucose tolerance or impaired glucose tolerance. Insulin-mediated glucose disposal was quantified by determining the insulin sensitivity index (ISI) in response to a low-dose, constant infusion of insulin (25 mU/kg x h) and glucose (4 mg/kg x min) for 150 min. The mean (+/-SEM) ISI [(mL kg(-1) min(-1)/pmol/L) x 10(3)] was significantly greater in those without a family history (30.3 +/- 2.3) as compared with nondiabetic volunteers with a family history of type 2 diabetes, whether they had normal glucose tolerance (17.0 +/- 7.2) or impaired glucose tolerance (9.5 +/- 1.4). In addition, basal NO levels, evaluated by the measurement of its stable end products [i.e. nitrite and nitrate levels (NO2-/ NO3-)], were significantly higher, and cyclic-GMP levels, its effector messenger, were significantly lower in those with a family history, irrespective of their degree of glucose tolerance, when compared with healthy volunteers without a family history of type 2 diabetes. Furthermore, when the 62 volunteers were analyzed as one group, there was a negative correlation between ISI and NO2-/NO3- levels (r = -0.35; P < 0.005) and a positive correlation between ISI and cyclic-GMP levels (r = 0.30; P < 0.02). These results have shown that alterations of the NO/cyclic-GMP pathway seem to be an early event in nondiabetic individuals with a family history of type 2 diabetes and these changes are correlated with the degree of insulin resistance.

Comparison of fasting plasma leptin concentrations in healthy subjects with high and low plasma insulin

This study was initiated to evaluate the role of hyperinsulinemia in the regulation of fasting plasma leptin. We measured plasma leptin and insulin concentrations in 404 healthy nondiabetic subjects. For analytical purposes, the population was divided into quartiles on the basis of the lowest (quartile 1) and highest (quartile 4) plasma insulin response to oral glucose, and fasting plasma leptin values in these 2 dichotomous groups were compared. The total plasma integrated insulin response was 4-fold greater in quartile 4, associated with significantly higher (P < .001) fasting plasma leptin (12.60+/-0.85 v8.53+/-0.56 ng/mL). Fasting plasma leptin concentrations remained significantly higher in the hyperinsulinemic quartile when comparisons were made after subdividing the population on the basis of gender, body mass index (BMI), or waist to hip ratio (WHR). These results demonstrate that fasting plasma leptin concentrations are significantly higher in hyperinsulinemic individuals, and this difference is independent of either overall or central obesity.

Hyperinsulinemia in a normal population as a predictor of non-insulin-dependent diabetes mellitus, hypertension, and coronary heart disease: the Barilla factory revisited

The study was initiated to evaluate the ability of hyperinsulinemia (as a surrogate measure of insulin resistance) to predict the development in a previously healthy population of three putative outcomes of this abnormality--glucose intolerance, hypertension, and coronary heart disease (CHD). The study involved defining the incidence at which these changes occurred between 1981 and 1993 to 1996 in 647 individuals who were free of any disease when initially studied. The study population consisted of approximately 90% of the subjects evaluated in 1981, divided into quartiles on the basis of the plasma insulin response to a glucose challenge as determined in 1981. The results indicated that the 25% of the population with the highest insulin response in 1981 had significant (P < .001) increases in the incidence of impaired glucose tolerance (IGT) or type 2 diabetes (eightfold), hypertension (twofold), or CHD (threefold). Furthermore, the ability of hyperinsulinemia to predict the three clinical endpoints was independent of differences in age, gender, or body mass index (BMI). Finally, if CHD is considered the clinical endpoint, multiple logistic regression analysis indicates that the values for plasma triglyceride (TG) and mean arterial blood pressure ([MAP] as measured in 1981) also predict the development of CHD. These results indicate that the untoward clinical effects of insulin resistance and/or compensatory hyperinsulinemia, glucose intolerance, hypertension, and CHD clearly can develop in less than 15 years.

Can weight gain in healthy, nonobese volunteers be predicted by differences in baseline plasma insulin concentration?

In this study, we have evaluated the effect, over approximately 14 yr, of differences in baseline degree of hyperinsulinemia on weight gain in 647 healthy, nonobese factory workers. The subjects were divided into 4 quartiles, on the basis of their plasma insulin response to an oral glucose challenge, in 1981. At that time, the mean (+/-SD) plasma insulin concentration, 2 h after the glucose challenge, varied from 18+/-5 to 106+/-42 microU/mL. Despite this approximate 6-fold difference in plasma insulin response at baseline, the weight gain over the period of observation was similar in all quartiles, with mean (+/-SD) increments (kg) of 1.8+/-5.1, 1.6+/-5.3, 2.3+/-5.2, and 2.3+/-5.7, going from the lowest quartile to the highest quartile, in terms of insulin concentration. Furthermore, when the population was considered as a whole, there was no correlation between baseline degree of hyperinsulinemia and change in either absolute (r = 0.004) or percent (r = 0.003) weight gain. Finally, there was no difference in the number of individuals who gained more than 4.5 kg, as a function of their baseline insulin response. Consequently, we conclude that 6-fold differences in plasma insulin responses to glucose do not predict weight gain in a healthy, nonobese population.

Dissociation between urinary albumin excretion and variables associated with insulin resistance in a healthy population

OBJECTIVES

To see if the cluster of metabolic and haemodynamic variables defined as comprising Syndrome X varied as a function of urinary albumin excretion (UAE) rate in a healthy population.

DESIGN

A cross-sectional, population-based study.

SETTING

A factory in Italy.

SUBJECTS

Two hundred and twenty-five healthy volunteers, 115 men and 110 women. OUTCOME MEASURES. Measurements were made of the plasma glucose and insulin responses to oral glucose, fasting triglyceride (TG) and high density lipoprotein (HDL)-cholesterol concentrations, blood pressure, and UAE rates.

RESULTS

Only five of the 225 volunteers had micro-albuminuria, defined as a UAE rate > 2 micrograms min-1, and the UAE rate was < 5 micrograms min-1 in 80% of the volunteers. Significant variations in the metabolic and haemodynamic variables measured were not associated with any differences in UAE. Finally, significant relationships were found between various measures of plasma insulin concentration and plasma glucose response to oral glucose, plasma TG and HDL-cholesterol concentrations, and mean arterial blood pressure, independent of variations in age, body mass index, ratio of waist-to-hip girth, and UAE rates.

CONCLUSION

The widespread variability in plasma glucose and insulin responses, plasma TG and HDL-cholesterol concentrations, and blood pressure that are seen in the population at large cannot be attributed to variations in UAE rate.

Renal metabolism of C-peptide in patients with early insulin-dependent diabetes mellitus

Renal metabolism of C-peptide was studied in 6 patients with early insulin-dependent diabetes mellitus (IDDM) with residual beta cell activity and in 11 nondiabetic subjects by the arterial-venous difference technique both in the postabsorptive state and for 80 min after ingestion of an amino acid mixture (0.8 g/kg). Urinary C-peptide (Cp) excretion, glomerular filtration rate and renal plasma flow were also measured. In the postabsorptive state in IDDM, renal uptake of Cp is reduced, while its urinary excretion and clearance are significantly increased. As a result, net renal extraction is markedly reduced. In contrast to controls, renal uptake and net extraction of C-peptide after amino acid ingestion do not increase in patients; the peritubular uptake evident in normal subjects is not detectable. Urinary excretion and clearance of Cp remain significantly higher in IDDM patients. In both groups, renal uptake of C-peptide is directly related to its renal load: however, in IDDM, the increase in Cp uptake for each increment in renal load is 35% lower than in controls (p < 0.001). Furthermore, as opposed to controls, urinary Cp excretion is not correlated with its arterial levels. Therefore IDDM patients have marked defects in renal handling of endogenous Cp, regarding both the amount metabolized by renal tissue and that reabsorbed by tubular cells. These data indicate an early alteration in the diabetic kidney that also impairs the reliability of urinary Cp evaluation as an index of residual beta cell activity in IDDM patients.

Association between salt sensitivity and insulin concentrations in patients with hypertension

This study was performed in 28 patients with mild to moderate hypertension, classified as being either salt sensitive or salt resistant on the basis of the percent decrement in mean arterial blood pressure (MAP) seen 7 days after daily salt intake was decreased from 220 to 30 mmol/L. Ten patients had a percent decrease of MAP > 10% and were defined as being salt sensitive. Salt resistance was defined as a percent decrease in MAP of < 3% and eight patients satisfied this criterion. Both plasma glucose and insulin concentrations following a 75-g oral glucose challenge were significantly higher after the high-salt diet in the salt-sensitive patients. Furthermore, there were correlations of marginal statistical significance between the decrease in MAP after the low-salt diet and the plasma glucose (r = 0.32, P < .10) and insulin (r = 0.38, P < .06) responses to oral glucose. These data are consistent with the view that there is an association between resistance to insulin-mediated glucose disposal and salt sensitivity in patients with high blood pressure.

Comparison of the metabolic changes in rats with hypertension secondary to fructose feeding or renal artery stenosis

Hypertension was induced in rats by either renal artery stenosis or a fructose-enriched diet, and the consequent changes in plasma glucose, insulin, and triglyceride (TG) concentrations, and the steady-state plasma insulin (SSPI) and glucose (SSPG) concentrations in response to a 180-min continuous infusion of glucose and insulin in these two groups of hypertensive rats, were compared to values in a sham-operated group with normal blood pressure. Mean (+/- SEM) blood pressure was significantly higher than the control values (121 +/- 3 mm Hg) at the end of the study in rats with renal artery stenosis (178 +/- 13 mm Hg) and fructose-fed rats (151 +/- 5 mm Hg), whereas left ventricular weight was only significantly (P < .01) higher in rats with renal artery stenosis. Plasma glucose concentration was the same in all three groups, but fructose-fed rats had significantly higher plasma insulin (59 +/- 7 microU/mL) and TG (317 +/- 48 mg/dL) concentration than either sham-operated rats (30 +/- 4 microU/mL and 121 mg/dL) or rats with renal artery stenosis (34 +/- 5 microU/mL and 124 +/- 14 mg/dL). Although SSPI concentrations were similar (approximately 250 microU/mL) in all three groups of rats, SSPG concentrations were significantly higher (P < .01) in the fructose-fed rats (187 +/- 10 mg/dL) than in either sham-operated normotensive rats (120 +/- 6 mg/dL) or hypertensive rats with renal artery stenosis (133 +/- 4 mg/dL). Thus, insulin resistance, hyperinsulinemia, and hypertriglyceridemia developed in rats with fructose-induced hypertension, whereas none of these changes were seen in rats with renal artery stenosis.

Hyperinsulinaemia, obesity, and syndrome X

OBJECTIVE

The major aim of this study was to compare various aspects of carbohydrate, insulin, and lipoprotein metabolism, serum uric acid concentration, and blood pressure in normal subjects stratified on the basis of both plasma insulin concentration and degree of obesity. The hypothesis to be tested was that hyperinsulinaemia, per se, was associated with relative glucose intolerance, higher triglyceride and uric acid concentrations, lower high-density lipoprotein cholesterol concentration and higher blood pressure, irrespective of degree of obesity.

DESIGN

This represents a case-control study, in which normal volunteers were subdivided into four equal groups based upon degree of obesity and plasma insulin response to a 74 g oral glucose challenge.

SETTING

The study was performed in the out-patient clinic of a university hospital.

SUBJECTS

Sixty-four individuals were recruited for this study, subdivided into four groups based upon their plasma insulin concentration and body mass index. Subjects were classified as hyperinsulinaemic if their plasma insulin concentrations in response to an oral glucose challenge were more than two standard deviations above the mean of 732 volunteers previously studied [1]. Obesity was defined as a body mass index of > 30 kg m-2, and individuals were classified as non-obese if their body mass index was < 27.0 kg m-2. Based upon these criteria, four experimental groups were created: (i) non-obese hyperinsulinaemic (NOB hyper); (ii) obese hyperinsulinaemic (OB hyper); (iii) non-obese normoinsulinaemic (NOB normo); and (iv) obese normoinsulinaemic (OB normo).

MAIN OUTCOME MEASURES

Subject groups were compared on the basis of the integrated plasma glucose response to a 75 g oral glucose challenge, fasting plasma triglyceride, cholesterol, high-density lipoprotein cholesterol, and uric acid concentrations, and blood pressure.

RESULTS

Mean (+/- standard error of the mean) integrated plasma glucose response area for 2 h following a 75 g oral glucose load was significantly higher (13.4 +/- 0.4 vs. 11.0 +/- 0.4 mmol l-1, P < 0.001) in the hyperinsulinaemic group, as were the fasting triglyceride levels (2.4 +/- 0.2 vs. 1.4 +/- 0.1 mmol l-1, P < 0.001) and uric acid (5.3 +/- 0.2 vs. 4.4 +/- 0.2 mmol l-1, P < 0.05) concentrations. In contrast, high-density lipoprotein concentrations were lower in the hyperinsulinaemic group (1.06.0.05 vs. 1.32 +/- 0.05 mmol l-1, P < 0.001). In addition, blood pressure was higher in the hyperinsulinaemic group (136 +/- 5/87 +/- 2 vs. 123 +/- 2/82 +/- 1 mmHg, P < 0.05). Furthermore, when each of the two groups were divided into obese (n = 16) and non-obese (n = 16) groups, all of the differences outlined above persisted. These changes were independent of age, gender distribution, generalized and abdominal obesity, cigarette smoking, and estimated physical activity.

CONCLUSIONS

The cluster of changes subsumed under the heading of syndrome X are closely associated with hyperinsulinaemia (and presumably insulin resistance), and can be discerned irrespective of degree of obesity.

Changes in insulin and lipid metabolism in males with asymptomatic hyperuricaemia

OBJECTIVES

To define the effect of asymptomatic hyperuricaemia on various facets of glucose, insulin, and lipoprotein metabolism.

DESIGN

Case control study in health volunteers.

SETTING

The volunteers for this study were selected on the basis of their laboratory results from a larger population participating in a general survey in one large factory.

SUBJECTS

The study population consisted of 40 healthy males: 20 with asymptomatic hyperuricaemia (serum uric acid concentration equal to or greater than 420 mmol l-1) and 20 with normal serum uric acid concentrations (180-320 mmol l-1). The two groups were similar in terms of age, general obesity (estimated by body mass index), smoking and alcohol intake, and estimate of work and leisure time activity.

INTERVENTIONS

All subjects received a 75 g oral glucose challenge, with blood taken before and at frequent intervals thereafter.

MAIN OUTCOME MEASURES

Fasting plasma glucose, insulin, and lipid concentrations and plasma glucose and insulin responses to the oral glucose challenge.

RESULTS

By selection, mean (+/- SEM) serum uric acid concentration was higher in the hyperuricaemic individuals (454 +/- 7 vs. 274 +/- 12 mmol l-1). In addition, the plasma insulin response to oral glucose was increased in individuals with asymptomatic hyperuricaemia (P < 0.005) as were both systolic (136 +/- 3 vs. 126 +/- 3 mmHg, P < 0.05) and diastolic (91 +/- 1 vs. 82 +/- 1, P < 0.01) blood pressure. Furthermore, subjects with asymptomatic hyperuricaemia were dyslipidaemic (higher plasma TG and cholesterol and lower HDL-cholesterol concentrations) as compared to the normouricaemic control group (P < 0.07-0.005).

CONCLUSIONS

These results provide a possible explanation for the well-known association of hyperuricaemia with coronary heart disease, as well as suggesting that hyperuricaemia be added to the cluster of metabolic and haemodynamic abnormalities associated with insulin resistance and/or hyperinsulinaemia and designated as Syndrome X.

Prevalence of hyperinsulinaemia in patients with high blood pressure

A total of 41 patients with hypertension were identified in a survey of 732 healthy factory workers. Twenty-three of these individuals were receiving antihypertensive medication, whereas 18 cases were newly discovered. Plasma glucose and insulin responses to oral glucose and fasting plasma triglyceride (TG), cholesterol, and high-density-lipoprotein (HDL) cholesterol concentrations of these 41 individuals were compared with those of 41 other factor workers, with normal blood pressure, matched with the hypertensive group in terms of gender, age, degree of obesity, job in the factory, and leisure-time activity. Patients with hypertension had significantly higher plasma glucose (P less than 0.05) and insulin (P less than 0.05) concentrations in response to oral glucose, as well as a higher plasma TG concentration (P less than 0.05). Similar findings were obtained when the treated and untreated hypertensive groups were analysed separately and compared with their respective control groups. However, there were no differences between the treated and untreated hypertensive groups. Ninety per cent of the normotensive group had a plasma insulin concentration of less than 500 pmol l-1 2 h after the glucose load. Using this value as the criterion for definition of hyperinsulinaemia, 41% of the patients with high blood pressure were hyperinsulinaemic. In addition to meeting this cut-off point, the patients with hypertension and hyperinsulinaemia were also glucose intolerant and dyslipidaemic. In conclusion, approximately 50% of an unselected group of patients with hypertension were hyperinsulinaemic. Insulin levels were comparable in treated and untreated patients with high blood pressure, and hyperinsulinaemic patients also tended to be glucose intolerant and dyslipidaemic.

Abnormalities of insulin and lipid metabolism in Milan hypertensive rats

Plasma glucose, insulin, triglyceride, and cholesterol concentrations were measured in male rats of the Milan hypertensive strain (MHS) and compared to the Milan normotensive strain (MNS) of the same body weight. Both blood pressure (P less than .001) and left ventricular weight (P less than .005) were higher in rats of the MHS. Although plasma glucose concentrations were similar in both groups, mean (+/- SEM) plasma insulin concentration were significantly higher (P less than .01) in MHS as compared to MNS rats (30 +/- 4 v. 13 +/- 5 microU/mL). In addition mean (+/- SEM) plasma triglyceride concentrations were higher (P less than .01) in MHS rats (112 +/- 9 mg/dL) than in MNS rats (81 +/- 6 mg/dL), as were plasma cholesterol concentrations (114 +/- 3 v 100 +/- 2 mg/dL, P less than .001). These data demonstrate the presence of hyperinsulinemia and hypertriglyceridemia in another genetic model of rat hypertension.

Insulin-resistance and associated risk factors for coronary heart disease as seen in families

Recent reports have shown that resistance to insulin-stimulated glucose uptake, increased plasma glucose and insulin response to oral glucose, and hypertriglyceridemia can be seen in first degree relatives of patients with type 2 diabetes. We have recently shown that very similar metabolic changes can be seen in hyperinsulinemic individuals who have either normal or impaired glucose tolerance (IGT). Given these data, we thought it would be of interest to compare the plasma glucose and insulin response to an oral glucose challenge, plasma lipid concentrations, and blood pressure in offspring of parents with IGT as compared to offspring of parents with normal glucose tolerance. Parents with IGT had higher plasma insulin and triglyceride levels and blood pressure than those with normal glucose tolerance. The two groups of offspring were young, non-obese and similar in terms of age, gender distribution and body mass index. Statistically significant increases in plasma insulin response to oral glucose and in systolic and diastolic blood pressure were present in the offspring of parents with IGT. Demonstration of similar abnormalities in plasma insulin response to glucose and blood pressure regulation in patients with IGT and in their offspring is consistent with the view that individual differences in insulin metabolism and blood pressure are modulated by genetic factors and that both may be related to variations in insulin-stimulated glucose uptake and/or plasma insulin concentration.

Changes in blood pressure, plasma triglyceride and aldosterone concentration, and red cell cation concentration in patients with hyperinsulinemia

Blood pressure, plasma concentration of triglyceride, aldosterone, renin activity (PRA), and atrial naturietic peptide (ANP), and red blood cell, urine, and plasma sodium and potassium concentration were determined in 24 healthy individuals divided into two groups defined as being either hyperinsulinemic or normoinsulinemic. The results demonstrated that the hyperinsulinemic group had significantly higher values for both systolic (P less than .01) and diastolic (P less than .05) blood pressure. In addition, plasma concentrations of triglyceride (P less than .02), aldosterone (P less than .05) and potassium (P less than .05) were higher in hyperinsulinemic individuals as compared to those who were normoinsulinemic. Furthermore, red cell potassium was lower (P less than .01) and red cell sodium higher (P less than .01) in the hyperinsulinemic group. Finally, the magnitude of hyperinsulinemia correlated directly with systolic (r = 0.50, P less than .01) and diastolic (r = 0.44, P less than .05) blood pressure, concentration of plasma triglyceride (r = 0.55, P less than .01) and aldosterone (r = 0.46, p less than .05), and erythrocyte sodium concentration (r = 0.57, p less than .01). In contrast, plasma insulin response was negatively correlated with erythrocyte potassium concentration (r = 0.40, P less than 0.05). These observations provide further support for the view that hyperinsulinemia, presumably secondary to resistance to insulin-stimulated glucose uptake, is associated with a cluster of variables that may play important roles in the etiology and clinical course of hypertension.

High plasma insulin and triglyceride concentrations and blood pressure in offspring of people with impaired glucose tolerance

The plasma glucose and insulin response to an oral glucose challenge, fasting plasma lipid concentration, and blood pressure were compared in 13 offspring of parents previously diagnosed as having impaired glucose tolerance (IGT) and 13 offspring of parents previously shown to have normal glucose tolerance. The parents with IGT had higher plasma glucose, insulin and triglyceride concentration, and blood pressure than parents with normal glucose tolerance. The two groups of offspring were young and non-obese, and similar in terms of age, gender distribution, and body mass index. However, the total integrated plasma insulin response during a 75 g oral glucose tolerance test was significantly higher (p less than 0.05, Student's t-test) in offspring of parents with IGT (718 +/- 71 pmol l-1 h) than in the subjects whose parents had normal glucose tolerance (524 +/- 47 pmol l-1 h). In addition, serum triglyceride concentration was somewhat higher in offspring of parents with IGT (1.17 +/- 0.11 vs 0.92 +/- 0.08 mmol l-1, 0.10 greater than p greater than 0.05), as were both systolic (132 +/- 5 vs 118 +/- 3 mmHg, p less than 0.05) and diastolic (79 +/- 3 vs 70 +/- 2 mmHg, p less than 0.05) blood pressure. Demonstration of similar abnormalities in plasma insulin response to glucose and blood pressure regulation in patients with IGT and in their offspring is consistent with the view that these changes have a genetic component.

Habitual leisure-time physical activity is associated with differences in various risk factors for coronary artery disease

Various risk factors for coronary artery disease (CAD) were compared in 100 healthy, male factory workers, divided into two groups of 50 each on the basis of their leisure-time activity. The two groups, designated as sedentary and physically active, were similar in terms of age and body mass index, but the physically active group had a significantly slower pulse rate. In addition, the plasma glucose and insulin responses to an oral glucose load were significantly lower in physically active individuals. Furthermore, fasting plasma triglyceride concentration was significantly lower and the high-density lipoprotein-cholesterol concentration was higher in the physically active individuals. Thus, substantial benefits in terms of CAD risk were associated with increased leisure-time physical activity.

Risk factors for coronary artery disease in healthy persons with hyperinsulinemia and normal glucose tolerance

We studied the relation of serum insulin levels to plasma lipid levels and blood pressure in two groups drawn from among 247 healthy, normotensive nonobese subjects with normal glucose tolerance. One group of 32 subjects was defined as having hyperinsulinemia (serum insulin, greater than 2 SD above the mean) and then compared with 32 normoinsulinemic subjects (serum insulin within 1 SD of the mean) matched for age (mean, 39 years), sex (22 men and 10 women), and body-mass index (24.7). The two groups had similar patterns of smoking, drinking, and physical exercise. Plasma glucose levels after an oral glucose challenge were significantly higher (P less than 0.05) in the hyperinsulinemic group. In addition, the mean (+/- SEM) fasting plasma triglyceride levels in subjects with hyperinsulinemia were significantly higher (1.73 +/- 0.2 vs. 1.24 +/- 0.1 mmol per liter) and the plasma high-density lipoprotein cholesterol concentrations were lower (1.21 +/- 0.06 vs. 1.43 +/- 0.06 mmol per liter) than in subjects with normoinsulinemia. Both systolic (126 vs. 119 mm Hg; P less than 0.05) and diastolic (85 vs. 78 mm Hg; P less than 0.01) blood pressures were significantly elevated in the group with hyperinsulinemia. We conclude that healthy persons with hyperinsulinemia and normal glucose tolerance have an increase in risk factors for coronary artery disease, as compared with a well-matched group of healthy subjects with normal insulin levels.

Evidence that multiple risk factors for coronary artery disease exist in persons with abnormal glucose tolerance

Multiple risk factors for coronary artery disease were determined in 50 healthy, non-diabetic persons with an oral glucose tolerance test result that could not be classified as normal by current criteria and 50 sex-, age-, and weight-matched persons with normal oral glucose tolerance. The results indicated that persons with abnormal oral glucose tolerance were hyperinsulinemic, as well as hypercholesterolemic and hypertriglyceridemic. In addition, patients with abnormal results in glucose tolerance tests had significantly elevated systolic blood pressure and heart rates. These data suggest that a cluster of risk factors for coronary artery disease exists in non-diabetic persons with abnormal oral glucose tolerance.

Renal metabolism of C-peptide in man

Renal metabolism of C-peptide was studied in nine nondiabetic nonobese patients with normal renal function by the arterial-venous difference technique before and after the oral administration of an amino acid mixture simulating an animal protein meal. In the basal state, the kidney removed 25.7 +/- 7.5% (+/- SD) of the arterial plasma C-peptide. Renal uptake was approximately 7-fold greater than urinary excretion, and thus, more than 85% of the amount extracted was metabolized by the kidney. Renal C-peptide clearance was very high and approximated the glomerular filtration rate, whereas urinary C-peptide clearance was only 14% of its renal clearance. Shortly after amino acid ingestion, arterial C-peptide levels increased by 107%, and C-peptide renal fractional extraction, uptake, and net metabolism also increased markedly (67%, 278%, and 328%, respectively); urinary clearance and excretion did not change. Renal clearance became 2-fold greater than the glomerular filtration rate, indicating that in this phase the kidney removed substantial amounts of C-peptide from peritubular blood as well as by filtration. Both renal uptake and urinary excretion of C-peptide were related to its arterial levels (P less than 0.001 and P less than 0.05, respectively), but renal uptake increased much more than urinary excretion for each increment in arterial C-peptide levels. These results indicate that renal C-peptide metabolism is considerable in the postabsorptive state and is even more marked during the postprandial period. The kidney, therefore, plays a key role in both the regulation of circulating plasma levels and the metabolic clearance of C-peptide.

Relationship between blood pressure and plasma insulin in non-obese and obese non-diabetic subjects

In this study, we have measured plasma insulin at fasting and following an oral glucose load and blood pressure after glucose load in 367 (247 non-obese, 120 obese) normotensive and untreated mildly hypertensive subjects. Overall, there was no independent association between fasting plasma insulin levels and blood pressure values. After controlling for age and body weight, a significant relationship between postglucose plasma insulin levels and diastolic blood pressure was found. When non-obese and obese subjects were examined separately, significant relationships were identified between postglucose plasma insulin levels and both systolic and diastolic blood pressure values in the former but not in the latter. A comparison of sex-, age-, and weight-matched hyperinsulinaemic vs normoinsulinaemic subjects showed that the former had significantly higher values of blood pressure only if not obese. These results demonstrate that the plasma insulin response to glucose is independently correlated with blood pressure.

Influence of the menstrual cycle on glucose tolerance and insulin secretion

To evaluate the impact of the menstrual cycle on glucose tolerance and insulin secretion, in the present study we have measured the plasma concentrations of glucose, insulin, and C-peptide during a 2-hour oral glucose tolerance test in 110 healthy, nonobese, regularly menstruating women. Fifty-five women were in the follicular phase, and 55 were in the luteal phase of the cycle. The two groups were well matched for age and body weight. Plasma concentrations of glucose, insulin, and C-peptide either in the fasting state or after the oral glucose load did not differ in the two groups. These results suggest that in nondiabetic women the menstrual cycle has no major effect on glucose tolerance and insulin secretion and that the phase of the menstrual cycle should not be considered in programming and interpreting an oral glucose tolerance test.

Relationships between insulin secretion, insulin metabolism and insulin resistance in mild glucose intolerance

The aim of this study was to evaluate whether the correlation between insulin resistance and peripheral hyperinsulinaemia existing in mild glucose intolerance corresponds to a relationship between insulin resistance and insulin overproduction by the pancreas. In addition, the possibility that insulin resistance is related to insulin metabolism was examined. Twenty five subjects with fasting normoglycaemia and an abnormal glucose response to the oral glucose tolerance test (OGTT) were studied. Insulin secretion by the pancreas was estimated by means of fasting C-peptide levels in peripheral blood. Insulin resistance was estimated by the rate of glucose disappearance from plasma after i.v. insulin injection. Insulin metabolism was estimated indirectly by the C-peptide: insulin molar ratio. A negative correlation was found between the glucose disappearance rate from plasma after i.v. insulin injection and fasting insulin levels (r = -0.677, p less than 0.001), but not fasting C-peptide concentrations (r = -0.164, p = NS). Glucose disappearance rate from plasma correlated positively with the C-peptide: insulin molar ratio (r = 0.626, p less than 0.001). These results suggest that in mild glucose intolerance insulin resistance and insulin secretion by the pancreas are not related phenomena, and that the defect responsible for insulin resistance might also be implicated in the impaired insulin metabolism.

Fractional hepatic extraction of insulin in man: is it constant?

The present study was designed to compare insulin extraction by the liver following oral glucose administrations of different size, in order to evaluate insulin removal by the liver in relation to the insulin exposure, and to the amount of ingested glucose. Insulin secretion by the pancreas was estimated by the measurement of peripheral C-peptide levels, and insulin extraction by the liver by the analysis of peripheral C-peptide to insulin ratios and relations. Ten healthy subjects (5 males and 5 females), aged 16 to 66 yr, with normal bw, and without family history of diabetes mellitus were investigated by means of the administration, on alternate days, of 50 and 150 g oral glucose loads. After the 150 g oral glucose load plasma glucose levels were significantly higher than after the 50 g oral glucose administration: glucose incremental areas of 1.45 +/- 0.12 vs. 0.55 +/- 0.04 mmol/l X min, respectively (p less than 0.001). Similarly, insulin concentrations were significantly higher following 150 g than after 50 g glucose ingestion: insulin incremental areas of 0.52 +/- 0.09 vs. 0.20 +/- 0.04 nmol/l X min (p less than 0.001). Also C-peptide levels were higher after 150 vs. 50 g oral glucose load: C-peptide incremental areas of 1.85 +/- 0.41 vs. 0.64 +/- 0.13 nmol/l X min (p less than 0.01). C-peptide to insulin molar ratios were similar during the two glucose challenge, and averaged 5.25 +/- 0.42 vs. 5.08 +/- 0.50 after 50 and 150 g oral glucose loads, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Further evidence that insulin metabolism is a major determinant of peripheral insulin response to oral glucose in subjects with mild glucose intolerance

In mild glucose intolerance plasma concentration of C-peptide seems to give an estimate of pancreatic B cell secretion more reliable than plasma insulin itself. In the present study we measured the plasma levels of insulin and C-peptide after oral glucose load in 100 mildly glucose intolerant subjects, focusing our attention on high and low insulin responders. According to an insulin incremental area after oral glucose higher or lower than the mean +/- SD of the mean, 16 subjects were classified as "high insulin responders", and 17 as "low insulin responders". The two groups were similar for sex, age and bw. Mean insulin incremental area was almost 9-fold greater in high insulin responders than in low insulin responders (0.88 +/- 0.03 vs 0.10 +/- 0.01 pmol/ml min, p less than 0.001). Also mean C-peptide incremental area was significantly greater in high insulin responders than in low insulin responders, but the differences between the two groups were smaller. Indeed, mean C-peptide area was approximately 2.5-fold greater in high insulin responders than in low insulin responders (1.58 +/- 0.12 vs 0.66 +/- 0.07 pmol/ml min, p less than 0.001). These results give further support to the concept that in mild glucose intolerance insulin metabolism is a major determinant of peripheral insulin response to oral glucose load.