Association of fasting insulin with blood pressure and lipids in young adults. The CARDIA study

Studies in hypertriglyceridaemia. 1. Serum triglyceride distribution and its correlates in randomly selected Swedish middle-aged men

OBJECTIVES

To obtain a randomly selected hypertriglyceridaemic population for detailed further characterization.

DESIGN

Study of randomly selected males.

SETTING

Subjects examined and blood sampled at Sollentuna Primary Health Care Centre.

SUBJECTS

Men aged 40-50 years (n = 1564), living in the Stockholm area, who were screened for hypertriglyceridaemia, January 1990-June 1992.

MAIN OUTCOME MEASURES

Fasting concentrations of serum triglycerides.

RESULTS

The serum triglyceride concentration distribution showed the expected skew distribution with the 90th and the 95th percentile at 2.51 and 3.05 mmol L-1, respectively. The mean serum triglyceride level compared well with several population values reported from this laboratory over the last 30 years, indicating stable triglyceride levels over time. There was no significant age-trend for the triglyceride concentration. Lower mean values for triglyceride, insulin and waist-to-hip (W/H) ratio were observed during the summer, whilst apolipoprotein A-I levels were higher. There was a linear relation between the number of cigarettes smoked and the serum triglyceride concentration. In stepwise multiple linear regression analysis with the triglyceride concentration as the dependent variable the following variables appeared as significant (P < 0.01) contributors: insulin, cholesterol, glucose, apolipoprotein A-I, number of cigarettes smoked, BMI, W/H ratio and diastolic blood pressure. The regression coefficient for apolipoprotein A-I was negative; all the others were positive. The multiple regression (R) was 0.68, suggesting that up to 47% of the variation of the serum triglyceride concentration could be predicted by these factors.

CONCLUSIONS

A group of randomly selected hypertriglyceridaemic men has been recruited for further clinical, metabolic and genetic studies. Basic characteristics of the population for their recruitment are described.

Insulin resistance, lipoproteins, body fat and hemostasis in nonobese men with angina and a normal or abnormal coronary angiogram

OBJECTIVES

The aim of this study was to compare metabolic risk factors in men with anginal chest pain and a normal or abnormal coronary angiogram with those in healthy men.

BACKGROUND

Risk factors for coronary heart disease, including lipoprotein abnormalities, hypertension and adiposity, may be metabolically interlinked, with insulin resistance and hyperinsulinemia being pivotal to these disturbances.

METHODS

Glucose and insulin metabolism, lipids and lipoproteins, hemostasis, blood pressure and body fat distribution were measured in 77 nonobese middle-aged men who had anginal chest pain (39 with an abnormal coronary angiogram and 38 with no detectable angiographic abnormality) and were compared with those of 40 healthy men of similar age and body mass index.

RESULTS

Patients with chest pain had higher insulin responses to an intravenous glucose challenge, lower insulin sensitivity, lower high density lipoprotein (HDL) and subfraction 2 cholesterol, lower apolipoprotein AI, higher triglycerides, greater android fat and higher systolic blood pressure at rest compared with levels in healthy control subjects (p < 0.05). Those with an abnormal coronary angiogram had lower tissue plasminogen activator levels, higher plasminogen activator inhibitor 1 levels and more android fat than did those with a normal angiogram (p < 0.05). Insulin sensitivity correlated positively with HDL (p < 0.05) and subfraction 2 (p < 0.001) cholesterol and negatively with triglycerides (p < 0.01), android fat proportion (p < 0.01) and systolic blood pressure (p < 0.05), whereas insulin response showed converse correlations.

CONCLUSIONS

These findings provide new evidence of the central role of insulin resistance and hyperinsulinemia in the development of risk factors associated with coronary heart disease.

Insulin and hypertension: are they related?

It has been postulated that insulin resistance and the concomitant compensatory hyperinsulinemia contribute to the pathogenesis of hypertension, possibly by stimulating the sympathetic nervous system, promoting renal sodium reabsorption, modulating cation transport, and/or stimulating vascular smooth muscle hypertrophy. The purpose of this article is to present a comprehensive up-to-date review of the literature and critically examine the insulin resistance-hyperinsulinemia-hypertension hypothesis.

Alcohol consumption and insulin concentrations. Role of insulin in associations of alcohol intake with high-density lipoprotein cholesterol and triglycerides

BACKGROUND

The relation between alcohol intake and insulin levels may explain, in part, the reported associations of alcohol with cardiovascular disease risk factors, including high-density lipoprotein (HDL) cholesterol, triglycerides, blood pressure, and glucose levels, each of which has been recognized as a component of the insulin resistance syndrome.

METHODS AND RESULTS

Subjects included nondiabetic participants of the Kaiser Permanente Women Twins Study (1989 through 1990). Usual alcohol intake was assessed as part of a food frequency questionnaire. For women from twin pairs in which both twins drank (n = 338), an increment of 12 g of alcohol per day (about one drink) was associated with an 8% lower 2-hour post-glucose-load insulin (P < .01) in a multiple regression analysis for twin data, adjusted for age, body mass index, waist-to-hip ratio, total caloric intake, and family history of diabetes. With genetic influences removed by matched analysis of the subset of 98 monozygotic twin pairs, an intrapair difference of 12 g of alcohol per day was associated with a 12.4% intrapair decrement in postload insulin (P < .01). Inverse associations were also seen for fasting insulin. Alcohol consumption was inversely associated with postload glucose but not with fasting glucose in unmatched (P = .05) and matched (P = .005) analyses. A significant positive association of alcohol intake with high-density lipoprotein cholesterol and an inverse relation of alcohol intake with triglycerides were each independent of insulin levels (P < or = .02 in the matched models). Neither systolic nor diastolic blood pressures were related to alcohol consumption in this sample, perhaps because of the rather low level of alcohol intake in the study population (median, 4 g/d).

CONCLUSIONS

Within the range of light to moderate drinking habits, alcohol consumption was inversely related to fasting and postload insulin levels. This relation did not explain associations of alcohol intake with lipid levels and may instead reflect an additional mechanism by which moderate alcohol consumption impacts cardiovascular disease risk.

Insulin-stimulated glucose utilization and borderline hypertension in young adult blacks

The purpose of this investigation was to determine whether there is a relation between impaired insulin-stimulated glucose utilization, or insulin resistance, and blood pressure (BP) in a young adult black population. Clinically well, young black men and women, including normotensive (BP < 135/85 mm Hg, n = 23) and borderline hypertensive (BP > or = 135/85 mm Hg, n = 27) individuals, were studied. Each subject had an oral glucose tolerance test (OGTT) and underwent a euglycemic hyperinsulinemic clamp procedure. A two-way analysis of variance demonstrated a significantly greater fasting insulin plasma concentration (P < .02) and sum of insulin levels during the OGTT (P = .04) in the borderline hypertensive compared with normotensive subjects. In both BP groups, women had significantly higher fasting plasma insulin levels than men (P < .02 and P = .009). Body mass index was a significantly covariate of the plasma insulin concentration. Data obtained from the clamp demonstrated significant insulin resistance in borderline hypertensive compared with normotensive subjects (4.69 +/- 0.50 versus 6.57 +/- 0.63 mg/kg per minute, P = .002). A stepwise multiple linear regression analysis demonstrated that there are significant multiple correlations of insulin resistance with body mass index, clamped insulin level, BP group, and systolic BP (multiple R = .7862, P < .001). Application of this analysis to the nonobese sample (n = 33) found significant correlations of insulin resistance with sex, BP group, and systolic BP (multiple R = .6817, P < .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Vascular insulin abnormalities, hypertension, and accelerated atherosclerosis

There is accumulating evidence that insulin resistance, glucose intolerance, and hyperinsulinemia exist in people with high blood pressure, and it has been suggested that insulin resistance and hyperinsulinemia may be of great importance in the origin of hypertension and its ultimate clinical course. Of importance are the recent observations that persons with normal glucose tolerance, selected on the basis of hyperinsulinemia, had higher blood pressure than matched individuals with normoinsulinemia. Hypertension in in insulin-resistant states generally has been attributed to hyperinsulinemia, with resulting increases in sympathetic nervous system activity. However, recent data from our laboratory suggest that cellular insulin resistance rather than hyperinsulinemia per se may lead to hypertension. The basic tenet proposed in this article is that a deficiency of insulin at the cellular level represents a common mechanism that is involved in the development of hypertension in both type I and type II diabetes mellitus. Insulin has an important role in the modulation of cellular calcium metabolism. Decreased insulin action on vascular smooth muscle cells may contribute both to hypertension and to accelerated atherosclerosis. Recent observations suggest that an impaired cellular response to insulin predisposes to increased vascular smooth muscle tone (the hallmark of hypertension in the diabetic state). For example, recently reported studies from our laboratory demonstrate that insulin attenuates the vascular contractile response to phenylephrine, serotonin, and potassium chloride. Thus, it appears that insulin normally modulates (attenuates) vascular smooth muscle contractile responses to vasoactive factors, and insulin resistance should accordingly be associated with enhanced vascular reactivity.

Hyperinsulinemia in hypertension: increased secretion, reduced clearance or both?

Peripheral hyperinsulinism is said to be associated and perhaps implicated in the pathogenesis of hypertension. There is however some inconsistency in the evidence of the relationship between insulin and blood pressure. We prospectively investigated glucose metabolism, insulin and C-peptide values and serum lipids in a large sample of hypertensive as compared with age and body habitus-matched normotensive subjects. As a group, the 145 hypertensives (blood pressure: 160/99 +/- 8.5/6.5 mmHg, mean +/- SD) had significantly elevated fasting plasma insulin (p < 0.02), total and LDL-cholesterol (p < 0.01) than 132 normotensive control subjects. The fasting HbA1c (glycated hemoglobin A1c)/insulin ratio, an estimate of insulin sensitivity, was significantly lower (5.15 +/- 1.45) in the hypertensives than normotensives (5.8 +/- 1.5, p < 0.001). Hypertensives had normal fasting C-peptide levels and lower C-peptide/insulin molar ratios, indicating low hepatic insulin extraction. There was no correlation between mean blood pressure (1/3 systolic + 2/3 diastolic) and fasting serum C-peptide (p = 0.14), insulin (p = 0.11), HbA1c/insulin ratio (p = 0.6), C-peptide/insulin ratio (p = 0.22) and HbA1c (p = 0.19), even after adjusting for age, BMI and family history of diabetes. The differences between hypertensives and normotensives persisted after dividing the subjects according to the presence/absence of either obesity or impaired glucose tolerance, but the significance was lost due to the smaller samples of the subgroups. The obese hypertensives with impaired glucose tolerance had the lowest values of insulin sensitivity and clearance in the fasting state.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin resistance in young salt-sensitive normotensive subjects

Insulin resistance has been demonstrated in patients with essential hypertension, and insulin-mediated sodium retention is believed to contribute to hypertension in these individuals. Recently, a hyperinsulinemic response to an oral glucose load has been found in salt-sensitive normotensive subjects, suggesting that insulin resistance may be present in these hypertension-prone individuals before the development of hypertension. In the present study, we examined the relation between insulin sensitivity and blood pressure response to salt intake in young, lean normotensive subjects on a high and a low salt diet. Insulin sensitivity was estimated by the "insulin suppression test," i.e., by measuring the plasma glucose and insulin concentrations achieved during a 180-minute infusion of somatostatin, insulin, and glucose in 18 healthy male volunteers (age, 21-28 years) given a standardized low salt diet (20 mmol/day) for 2 weeks, supplemented by either 220 mmol of NaCl per day or placebo in a single-blind randomized order for 1 week each. We defined salt sensitivity as a significant decrease in mean arterial blood pressure (> 3 mm Hg [p < 0.05]) measured for 60 minutes at 1-minute intervals on the low salt diet. By this definition, seven of the 18 subjects were salt sensitive. Although insulin infusion resulted in similar plasma insulin levels (approximately 50 milliunits/L) in both groups, concomitant glucose infusion resulted in plasma glucose levels that were more than 50% higher in the salt-sensitive than in the salt-resistant group (p < 0.005 by two-way analysis of variance).(ABSTRACT TRUNCATED AT 250 WORDS)

Relationships between blood pressure and lipids in childhood

This review has discussed the potential interrelationships of elevated blood pressure and lipid abnormalities. Most of the data for this review have been collected in adults, but physiologic and genetic effects may have expression in childhood. Clustering of cardiac risk factors may be mediated by increased levels of insulin. These increased levels of insulin may be genetically determined or may be related to obesity. Recognition of the multiple risk factor phenotype is important, because individuals with multiple risk may have a much higher risk of future coronary events than do individuals with single risk factors. Medical therapy of individuals with multiple risk should be more aggressive than for individuals with single risk factors. Physicians should be cautious about therapy in the pediatric setting because of possible interaction between therapeutic agents and risk factors, however.

Influence of insulin resistance, secretion, and clearance on serum cholesterol, triglycerides, lipoprotein cholesterol, and blood pressure in healthy men

Relations between serum lipids, lipoproteins, blood pressure, and insulin metabolism were investigated in 158 healthy men aged 19-77 years and with body mass indexes (BMIs) of 19-41 kg.m-2. Mathematical modeling analysis of glucose, insulin, and C-peptide concentrations during an intravenous glucose tolerance test was used to measure parameters of insulin metabolism. In univariate analysis, both fasting and postglucose insulin concentrations showed significant positive associations with fasting serum triglyceride levels (r = 0.33 and 0.38, respectively) and systolic (r = 0.22 and 0.26) and diastolic (r = 0.21 and 0.24) blood pressure and negative associations with high density lipoprotein subfraction 2 cholesterol (HDL2; r = -0.21 and -0.25). In multivariate analysis, the associations between insulin and HDL2 cholesterol concentrations were found to depend on triglyceride levels. Insulin resistance and basal pancreatic insulin secretion showed significant positive associations with serum triglycerides, which were independent of the effects of age, BMI, and fat distribution. Hepatic insulin throughout was independently associated with HDL2 cholesterol. Associations of insulin-related variables with blood pressure were generally dependent on age and BMI. These results underline the importance of insulin sensitivity and insulin concentrations as determinants of triglyceride metabolism. They also indicate a close relation between hepatic insulin handling and HDL2 concentration that is independent of triglyceride metabolism.

Distributed data analysis in a multicenter study: the CARDIA Study

Unlike distributed data entry, which is used in many large epidemiologic studies and multicenter clinical trials, distributed data analysis is a relatively new concept. This paper reports on the usefulness of such a system in the Coronary Artery Risk Development in Young Adults (CARDIA) Study. CARDIA distributes the entire examination dataset to participating centers soon after completion of each round of data collection. The process was designed to encourage more numerous, diverse, and rapid publications, and to allow for more efficient use of the manpower and expertise in centers. Responsibilities of the coordinating center have changed from a conventional coordinating center but remain substantial due to the need for collating, monitoring, verifying, and documenting the distributed data analysis (DDA) system. DDA is successful from the standpoint of implementation and operation--21 manuscripts representing work analyzed at six participating centers had been submitted for publication within 3.5 years of the completion of the baseline examination.

Hormonal and local factors in hypertension

The cause of primary (essential) hypertension remains unknown, but a number of circulating hormones and endothelium-derived factors are probably involved. This review summarizes recent evidence on the roles of hyperinsulinemia, the renin-angiotensin system, atrial natriuretic factor, and three endothelium-derived factors--prostacyclin, endothelium-derived relaxing factor, and endothelin.

Racial differences in the relation between blood pressure and insulin resistance

BACKGROUND

Insulin resistance and the concomitant compensatory hyperinsulinemia have been implicated in the pathogenesis of hypertension. However, reports on the relation between insulin and blood pressure are inconsistent. This study was designed to investigate the possibility of racial differences in this relation.

METHODS

We studied 116 Pima Indians, 53 whites, and 42 blacks who were normotensive and did not have diabetes; the groups were comparable with respect to mean age (29, 30, and 31 years, respectively) and blood pressure (113/70, 111/68, and 113/68 mm Hg, respectively). Insulin resistance was determined by the euglycemic-hyperinsulinemic clamp technique during low-dose (40 mU per square meter of body-surface area per minute) and high-dose (400 mU per square meter per minute) insulin infusions.

RESULTS

The Pima Indians had higher fasting plasma insulin concentrations than the whites or blacks (176, 138, and 122 pmol per liter, respectively; P = 0.002) and lower rates of whole-body glucose disposal during both the low-dose (12.7, 17.1, and 19.5 mmol per minute; P less than 0.001) and the high-dose (38.0, 43.1, and 45.7 mmol per minute; P less than 0.001) insulin infusions. After adjustment for age, sex, body weight, and percentage of body fat, mean blood pressure (calculated as 1/3 systolic pressure + 2/3 diastolic pressure) was significantly correlated with the fasting plasma insulin concentration (r = 0.42) and the rate of glucose disposal during the low-dose (r = -0.41) and high-dose (r = -0.49) insulin infusions (P less than 0.01 for each) in whites, but not in Pima Indians (r = -0.06, -0.02, and -0.04, respectively) or blacks (r = -0.10, -0.04, and 0.02, respectively).

CONCLUSIONS

The relations between insulinemia, insulin resistance, and blood pressure differ among racial groups and may be mediated by mechanisms active in whites, but not in Pima Indians or blacks.

Serum insulin and other cardiovascular risk indicators in children, adolescents and young adults

We wanted to determine the levels of fasting serum insulin during growth, the tracking of serum insulin, and the correlation of serum insulin with other coronary heart disease risk indicators in children and young adults. In 1986 2433 subjects, aged nine to 24 were studied, and insulin data were available from the same population in 1980 and 1983. Serum insulin levels showed a peak during puberty in both sexes and the decline in insulin continued after the age of 21. Tracking of serum insulin was only moderate, especially in females and young boys. Serum insulin correlated positively with body mass index, concentrations of serum triglycerides, and blood pressure, and inversely with the concentration of high density lipoprotein cholesterol. High triglycerides, high systolic blood pressure, and low level of high density lipoprotein cholesterol clustered among subjects within the highest insulin quartile. Our results suggest that the insulin resistance phenomenon, caused mainly by obesity and leading to unfavourable levels of other coronary heart disease risk indicators, is already developing in children and young adults. This suggests that preventing obesity in early life is important.

Are insulin and hypertension independently related?

Hyperinsulinemia has been proposed as the common pathogenetic mechanism of obesity, non-insulin-dependent diabetes mellitus, and hypertension. We examined the cross-sectional relationship between fasting and postchallenge insulin levels and hypertensive status in a population-based study of 653 men and 784 women, aged 50 to 93 years, in Rancho Bernardo, California. Hypertensive subjects had slightly but not significantly higher fasting plasma insulin levels than did normotensive subjects, but significantly higher postchallenge insulin levels. After stratification for obesity and glucose intolerance, there was no significant difference between the mean age-adjusted fasting or postchallenge insulin levels of those with and those without hypertension in 12 possible subgroups. Analysis of variance of both fasting and postchallenge insulin levels also failed to reveal a significant relationship between insulin and hypertensive status after adjusting for age, sex, body mass index, and diabetes. The current study does not support the hypothesis that insulin is independently associated with hypertension.

Racial and ethnic modifiers of the salt-blood pressure response

The relation between sodium and blood pressure is a centuries-old question. A substantial body of epidemiological and experimental data has accumulated that strongly implicates NaCl as having a causal role in the genesis of arterial hypertension. Prospective studies that have been performed in diverse populations that have manipulated NaCl exposure by diet or infusion have repeatedly documented an NaCl pressor effect. Further, similar studies in biracial populations have also demonstrated a greater prevalence of "salt sensitivity" in blacks compared with whites. The reasons for this observation are not entirely clear; however, intrinsic or hypertension-induced renal abnormalities that limit natriuretic capacity, reduced Na+,K(+)-ATPase pump activity, other membrane ion transport disturbances, differential exposure to psychological stressors, greater insulin resistance, and dietary factors (reduced Ca+ and K+ intake) have all been suggested as possibly playing a role. Salt sensitivity appears to be a widespread phenomenon. However, it is critically important to determine what factors account for racial differences in salt sensitivity. Moreover, the prevalence of salt sensitivity in the general population is unknown. Current definitions of salt sensitivity are varied and unidirectional. In comparison with bidirectional criteria (blood pressure increase with salt loading and blood pressure decrease with salt restriction), they are probably inadequate to identify salt-sensitive individuals who manifest less extreme blood pressure change after dietary sodium or plasma volume manipulations. More sensitive criteria for diagnosing salt sensitivity will facilitate a better understanding of racial and ethnic differences in the prevalence of salt sensitivity.