Serum insulin and ECG abnormalities suggesting coronary heart disease in the populations of Mauritius and Nauru: cross-sectional and longitudinal associations

Association of insulin resistance and glycemic measures with major abnormal electrocardiogram in older Chinese: Cross-sectional analysis based on the Guangzhou Biobank Cohort study

AIMS

To examine whether insulin resistance (IR) and glycemic measures were associated with major abnormal electrocardiogram (MA-ECG) and its specific abnormalities in the general population.

METHODS

Twelve-lead ECG measurements were performed on 21,720 participants without cardiovascular disease (5,918 men) from the Guangzhou Biobank Cohort Study. The participants were aged 50 years or above (mean age 61.6, standard deviation 7.1 years). Logistic regression was used to assess the associations of IR and glycemic measures with MA-ECG and specific abnormalities.

RESULTS

Ln-fasting insulin was significantly associated with MA-ECG and ST-T abnormalities (adjusted odds ratio = 1.52, 95 % confidence interval = 1.15-2.02 and 1.83, 1.37-2.45, respectively, for per standard deviation), which were stronger than those of TyG index with MA-ECG (1.08, 1.04-1.13) and ST-T abnormalities (1.16, 1.11-1.22). Ln-fasting insulin had association with Q wave abnormalities (3.19, 1.52-6.67). The association of TyG index with prolonged QTc varied by sex and obesity (P for interaction ≤ 0.01). Participants with diabetes had stronger associations of ln-fasting plasma glucose with ECG abnormalities than those without.

CONCLUSIONS

IR and glycemic measures were associated with MA-ECG, ischemia and prolonged QTc in older Chinese, especially in women, those with obesity, and those with diabetes. These findings underscore the importance of regular evaluations for these groups.

Carotid artery intima-media thickness is associated with insulin-mediated glucose disposal in nondiabetic normotensive offspring of type 2 diabetic patients

The aim of this study was to investigate whether insulin resistance is independently associated with early manifestations of atherosclerosis. To this end, 176 normotensive offspring of type 2 diabetic patients were subjected to euglycemic hyperinsulinemic clamp to assess insulin sensitivity. Early atherosclerosis was studied by ultrasonography of the common carotid artery. Of the total 176 subjects, 145 were glucose tolerant, 18 had impaired fasting glucose, and 13 had impaired glucose tolerance. Univariate correlations showed that age, body mass index, waist, blood pressure, 2-h postchallenge glucose, fasting insulin, triglycerides, interleukin-6, fibrinogen, and white blood cell count were significantly correlated with carotid intima-media thickness (IMT), whereas HDL cholesterol and glucose disposal showed a negative correlation. A stepwise multivariate regression analysis including sex, age, waist circumference, smoking status, systolic blood pressure, diastolic blood pressure, triglyceride, HDL cholesterol, 2-h postchallenge glucose, plasma IL-6, fibrinogen, white blood cell count, insulin-stimulated glucose disposal, and fasting insulin showed that the four variables that remained significantly associated with carotid IMT were waist circumference, insulin-stimulated glucose disposal, white blood cell count, and diastolic blood pressure, accounting for 33.7% of its variation. These findings support the concept that insulin sensitivity, rather than plasma insulin levels, is associated with early atherosclerosis in nondiabetic normotensive offspring of type 2 diabetic patients.

Insulin treatment and cardiovascular disease; friend or foe? A point of view

BACKGROUND

Several observational studies have shown that higher insulin levels are associated with an increased risk of cardiovascular disease. If higher endogenous insulin levels are causally related to cardiovascular disease, one might expect an increased risk of cardiovascular disease in patients treated with insulin, as this results in high circulating insulin levels. Such risk elevation might counteract the benefits of tight glucose control. Our objective was to explore the relationship between insulin therapy and cardiovascular disease in Type 1 and Type 2 diabetes mellitus using information from available literature.

SUMMARY OF COMMENT

Several experimental studies in animals and humans support the presence of a harmful effect of insulin on the vascular endothelium. In prospective follow-up studies increased insulin dosage was associated with increased risks of cardiovascular disease, although confounding by indication could not be excluded. Randomized controlled trials in diabetic patients, comparing conventional with intensive glucose-lowering treatment, although showing a reduction in microvascular disease, showed no significant difference in the incidence of cardiovascular disease. The results with respect to exposure to insulin are, however, difficult to interpret due to insufficient information on exposure to insulin levels as well as confounding by glycaemic control and body mass index. In addition, these studies were not designed to address the question whether higher insulin use relates to increased cardiovascular risk.

CONCLUSION

Published research provides conflicting evidence as to whether exposure to high levels of exogenous insulin in diabetes mellitus affects the risk of cardiovascular disease. The currently available studies have a number of serious methodological restraints that limit accurate interpretation and conclusions in this area.

Plasma insulin and cardiovascular mortality in non-diabetic European men and women: a meta-analysis of data from eleven prospective studies

AIMS/HYPOTHESIS

We examined the association between plasma insulin and cardiovascular mortality in non-diabetic European men and women based on data from eleven prospective studies.

METHODS

The study population comprised 6156 men and 5351 women aged 30-89 years. Baseline measurements included oral glucose tolerance test, fasting and 2-h plasma insulin, and conventional risk factors. Cox models were used to calculate hazard ratios (HRs) and their 95% confidence intervals, and overall HRs were assessed by meta-analyses.

RESULTS

During the 8.8-year follow-up, 362 men and 70 women died from cardiovascular disease. The age- and smoking-adjusted overall HR of cardiovascular mortality for the highest vs the lower quartiles of fasting insulin was 1.58 (95% CI: 1.26-1.97) in men and 2.64 (1.54-4.51) in women. Adjusting for other risk factors in addition, the HR was 1.54 (1.16-2.03) in men and 2.66 (1.45-4.90) in women. For 2-h insulin these HRs were 1.28 (0.99-1.66), 1.87 (0.87-4.02), and 0.85 (0.60-1.21), 1.36 (0.53-3.45). The overall HRs for interquartile ranges for fasting and 2-h insulin, with full adjustment, were 1.13 (1.05-1.22) and 1.11 (1.01-1.23) in men, and 1.25 (1.08-1.45) and 1.11 (0.91-1.36) in women.

CONCLUSIONS/INTERPRETATION

Hyperinsulinaemia, defined by the highest quartile cut-off for fasting insulin, was significantly associated with cardiovascular mortality in both men and women independently of other risk factors. Associations between high 2-h insulin and cardiovascular mortality were weaker and non-significant. Weak positive associations of fasting and 2-h insulin with cardiovascular mortality over interquartile ranges were, however, more similar.

Hyperfibrinogenemia and metabolic syndrome in type 2 diabetes: a population-based study

BACKGROUND

It has been hypothesized that fibrinogen clusters with several components of the metabolic syndrome, thus increasing its cardiovascular risk. The aims of the present study were to assess in a large population-based cohort of patients with type 2 diabetes (1) variables associated with fibrinogen and (2) the relationship between hyperfibrinogenemia, a number of components of the metabolic syndrome, and coronary heart disease (CHD).

METHODS

We identified a cross-sectional, population-based cohort of 1574 patients with type 2 diabetes using multiple sources of ascertainment. Components of the metabolic syndrome were hypertension (systolic blood pressure > or = 160 mmHg and/or diastolic blood pressure > or = 95 mmHg and/or treatment with antihypertensive drugs), dyslipidemia (tryglicerides >2.82 mmol/l and/or HDL-cholesterol <1.03 mmol/l), hyperuricemia (uric acid >416 micromol/l) and increased albumin excretion rate (AER > or = 20 microg/min).

RESULTS

Fibrinogen increases with age, HbA(1c), smoking, hypertension and a number of components of the metabolic syndrome, even after adjustment for confounders. Prevalence of CHD increases linearly across quartiles of fibrinogen (from 26.1 to 40.6%, p=0.046). However, in logistic regression, after adjustment for both confounders and known risk factors for CHD, the role of fibrinogen is no more significant, whereas ORs for HbA(1c) between 6.8 and 8.8% and >8.8% vs values <6.8% are, respectively, 1.91 (95% CI 1.36-2.69) and 1.56 (1.07-2.27).

CONCLUSIONS

This population-based study shows that fibrinogen increases with age, HbA(1c), smoking, hypertension and a number of components of the metabolic syndrome, independent of major confounders. We also found that poor blood glucose control was associated with CHD.

Metabolic syndrome and ischemic heart disease in elderly men and women

Associations between metabolic syndrome components and prevalent ischemic heart disease (IHD) were investigated in a cross-sectional, community-based study of elderly men (n = 1,015) and women (n = 1,259) in Rancho Bernardo, California, in 1984-1987. In both sexes, there were significant positive associations between IHD defined by resting electrocardiogram criteria and age, systolic blood pressure, fasting and postchallenge hyperglycemia, total cholesterol/high density lipoprotein cholesterol (HDL cholesterol) ratio, and triglycerides and an inverse significant association with HDL cholesterol. High collinearity and interactions between serum insulin and metabolic syndrome variables were accounted for by uncorrelated principal components identified by factor analysis. In both men and women, three uncorrelated principal components were identified, representing a central metabolic factor (body mass index, fasting and 2-hour serum insulin, high serum triglycerides, and low HDL cholesterol), a glucose factor, and a blood pressure factor. In a multivariate model with age and sex, all three factors were significantly associated with IHD by electrocardiogram criteria; central metabolic factor (odds ratio (OR) = 1.6, p = 0.001), glucose factor (OR = 1.4, p < 0.001), blood pressure factor (OR = 1.2, p = 0.005), age (10 years) (OR = 1.8, p < 0.001), and female sex (OR = 0.5, p < 0.02). Similar results were obtained in analyses using clinically manifest IHD as the outcome. These results support the thesis that the metabolic syndrome exerts effects through different risk factors by different mechanisms.

Mitogenic factors accelerate later-age diseases: insulin as a paradigm

Some genes are expressed differently in earlier and later generations of most cell lines. Many diseases become clinically expressed only later in life, and show clustering of the age at onset in the affected siblings, which may be related to the changing expression with age of the genes involved. Because insulin and its receptor are extremely ancient and well preserved structures with almost universal mitogenic effects, insulin may serve a paradigm of this process. It is suggested that by stimulating cell proliferation, hyperinsulinemia speeds up the appearance of later generations of cells with different expression of the genes. Insulin resistance, accompanying any hyperinsulinemia and considered to be a pathogenetic factor of some common later-age diseases, involves only some biochemical, but not mitogenic effects of the hormone. In humans, high levels of insulin in blood are encountered both physiologically after meals and in many pathological conditions: insulin therapy inevitably causes peripheral hyperinsulinemia; in type 2 diabetes hyperinsulinemia precedes hyperglycemia by many years; hyperinsulinemia is an independent risk factor of atherosclerosis, of type 2 diabetes itself, of some forms of dementia and other diseases; obesity is an obligatory hyperinsulinemic condition. The opposite of hyperalimentation, i.e. calorie restriction (at least, in rodents) may exert its life-prolonging effects through decreasing insulinemia and therefore the rate of cell proliferation. Insulin is only one example, and different mitogens regulate proliferation of different cells. It is likely that growth factors in general accelerating the replication of cells, play a role in speeding up the appearance of later-age diseases involving these cells.

Insulin and risk of cardiovascular disease: a meta-analysis

BACKGROUND

Our purposes were to estimate the strength of the longitudinal relationship between hyperinsulinemia and cardiovascular diseases (CVD) from the available literature and to identify study characteristics that modify this relationship.

METHODS AND RESULTS

Articles were identified by means of a MEDLINE and Embase search and citation tracking. Eligible studies were prospective population-based cohort studies and nested case-control studies on the relationship between, on the one hand, fasting or nonfasting insulin levels and, on the other hand, myocardial infarction, death from coronary heart disease, and/or ECG abnormalities. Data were extracted pertaining to insulin measurements, type of outcome studied, adjustment for confounding, sex, mean age of the study population, follow-up period, insulin assay, and ethnic background (white or nonwhite). Associations of insulin and CVD were reexpressed in a uniform manner, an estimate of relative risk (RR) and 95% CI, to be used in meta-regression analyses. Twelve of 17 potentially eligible articles provided sufficient information. Overall, a weak positive association was found. The meta-analysis resulted in an estimated summary RR (95% CI) of 1.18 (1.08 to 1.29) for differences in insulin level, equivalent to the difference between the 75th and the 25th percentiles of the general population in The Netherlands. Ethnic background and type of insulin assay modified the relationship between insulin and CVD with borderline significance.

CONCLUSIONS

Hyperinsulinemia is a weak risk indicator for the occurrence of CVD. The relationship between hyperinsulinemia and CVD was modified by ethnic background and by the type of insulin assay involved.

The impact of gender and general risk factors on the occurrence of atherosclerotic vascular disease in non-insulin-dependent diabetes mellitus

While it is generally accepted that non-insulin-dependent diabetes mellitus (NIDDM) increases atherosclerotic risk, controversy remains as to whether this effect is greater for women than men (thus reducing the usual gender differential). Furthermore, it is unclear to what extent changes in general risk factors may account for this increased risk. The literature was reviewed with meta-analyses. Gender specific overall relative risks with 95% confidence intervals for coronary heart disease (CHD) mortality (ICD codes 410-414) were calculated. Similarly, overall gender specific odds ratios for prevalent myocardial infarction (MI) are presented. Data are generated from both fixed effects and random effects models. Frequency counts of studies showing specific cardiovascular disease (CVD) risk factor effects in diabetes are given as is the number of studies showing diabetes to be an independent risk factor. The overall relative risk (the ratio of men to women) for CHD mortality in diabetes was 1.46 (1.21-1.75) and 2.29 (2.05-2.55) in nondiabetes suggesting that the gender differential is reduced in diabetes. However, heterogeneity was high (P < 0.001). Exclusion of studies that were exclusively in elderly subjects eliminated heterogeneity (P > 0.05), but retained a separation of the confidence intervals. Overall odds ratios (men:women) show no suggestion of a diabetes effect on the gender difference for prevalent MI, 1.77 (diabetes) and 1.79 (no diabetes). The effects of six general CVD risk factors were unclear, although the largest study showed a clear effect of cholesterol, smoking, and blood pressure. All 10 studies in women report diabetes to be an independent risk factor as do 8 out of 12 studies in men. NIDDM reduces the gender differential in CHD mortality, but not for prevalent MI (or other end points). Although the effect of specific CVD risk factors is inconsistent across studies, this is likely to reflect limited sample size and power. The major three risk factors, cholesterol, blood pressure, and smoking, probably operate in NIDDM but do not fully explain the increased risk of CVD in NIDDM.

Distribution and correlates of insulin in elderly men. The Honolulu Heart Program

The role of insulin in cardiovascular disease is uncertain, and studies in elderly or minority populations are infrequent. Fasting and 2-hour insulin concentrations and their cross-sectional associations with cardiovascular risk factors were examined in 3562 elderly (aged 71 to 93 years) Japanese American men from the Honolulu Heart Program who were reexamined between 1991 and 1993. Insulin distributions were skewed (mean and median: 16.8 and 12 microU/mL for fasting; 117.2 and 93 microU/mL for 2-hour); fasting but not 2-hour insulin levels declined significantly with age (P < .0001 and P = .54, respectively). Factors most strongly correlated with insulin included measures of obesity, fat distribution, and levels of triglyceride, glucose (r = .38 to r = .50 fasting, r = .21 to r = .27 2-hour), and HDL cholesterol (r = -.41 and r = -.22, respectively). Other correlates included fibrinogen, hematocrit, heart rate, blood pressure, cigarettes per day (all positive), alcohol, physical activity, and forced vital capacity (negative). Associations were also evident across risk factor quintiles. Insulin levels were significantly elevated in men with hypertension and diabetes. In multiple linear regression analyses, log10 fasting insulin was positively and independently associated with body mass index, triglycerides, glucose, fibrinogen, hematocrit, heart rate, diabetes, and hypertension and negatively associated with HDL cholesterol, physical activity, and forced vital capacity. In general, results were similar for log10 2-hour insulin and when subjects who fasted < 12 hours or had diabetes were excluded. Substitution of medication use and blood pressure for hypertension indicated independent associations of medication use but not blood pressure with insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Is hyperinsulinaemia a central characteristic of a chronic cardiovascular risk factor clustering syndrome? Mixed findings in Asian Indian, Creole and Chinese Mauritians. Mauritius Noncommunicable Disease Study Group

The aim of the study was to investigate whether the constellation of cardiovascular disease risk factors, described as Insulin Resistance Syndrome, exists in the multi-ethnic population of Mauritius, and to assess whether hyperinsulinaemia is the key feature of this syndrome. A sample of 5080 Mauritian subjects (aged 25-74 years) was examined in a noncommunicable diseases survey in 1987. Survey procedure included an oral glucose tolerance test, and anthropometric, blood pressure, plasma lipids and serum insulin measurements. Abnormal glucose tolerance (diabetes and impaired glucose tolerance), general obesity, upper-body obesity, hypertension, low HDL-cholesterol, and hypertriglyceridaemia were defined as risk factor conditions. Mean values for a series of risk factor variables were compared between reference subjects (no risk factors) and those with a risk factor condition (either one condition only, or in combination with one or more others). Prevalence estimates for each risk factor condition in combination with three or more other conditions were three to four times greater than expected by chance, and levels of risk factors for subjects with more than one risk factor condition were further away from the reference levels than for those with just one condition. Fasting and 2-h serum insulin levels were elevated for each condition when in combination with others, or to a lesser extent when isolated. However, this was not the case for isolated hypertension where insulin levels were not elevated. When adjusted for age, sex, and body mass index, insulin levels were only significantly elevated in subjects with upper-body obesity if in association with general obesity.(ABSTRACT TRUNCATED AT 250 WORDS)