Factors of the metabolic syndrome: baseline interrelationships in the first follow-up cohort of the HDDRISC Study (HDDRISC-1). Heart Disease and Diabetes Risk Indicators in a Screened Cohort

Limited evidence for sympathetic neural overactivation in older patients with type 2 diabetes mellitus

Introduction

Mechanistic studies suggested that excess sympathetic activity promotes arterial hypertension while worsening insulin sensitivity. Older patients with type 2 diabetes are at particularly high cardiovascular and metabolic risk. However, data on sympathetic activity in this population is scarce.

Methods

We studied 61 patients with type 2 diabetes mellitus (22 women, 60.9 ± 1.4 years; 39 men, 60.9 ± 1.4 years). They had to have diabetes for at least 2 years, a hemoglobin A1c of 6.5-10%, a body-mass-index of 20-40 kg/m², and had to be treated with stable doses of metformin only. We recorded ECG, finger and brachial blood pressure, and muscle sympathetic nerve activity (MSNA).

Results

MSNA was 37.5 ± 2.5 bursts/min in women and 39.0 ± 2.0 bursts/min in men (p = 0.55). MSNA expressed as burst incidence was 52.7 ± 2.0 bursts/100 beats in women and 59.2 ± 3.1 bursts/100 beats in men (p = 0.21). Five out of 39 men (12.8%) and two out of 22 women (9.1%) exhibited resting MSNA measurements above the 95th percentile for sex and age. In the pooled analysis, MSNA was not significantly correlated with systolic blood pressure, diastolic blood pressure, body mass index, waist circumference, body composition, or HbA1c (r ² < 0.02, p > 0.26 for all).

Discussion

We conclude that relatively few older patients with type 2 diabetes mellitus exhibit increased MSNA. The large interindividual variability in MSNA cannot be explained by gender, blood pressure, body mass index, or glycemic control.

TG: HDL-C Ratio as Insulin Resistance Marker for Metabolic Syndrome in Children With Obesity

Insulin resistance (IR) is an important variable in the diagnosis of metabolic syndrome (MetS). Currently, IR is not part of the existing pediatric definition of MetS, instead elevated fasting blood glucose (FBG) is measured as an indicator of hyperglycemia. Arguably, many obese children with severe IR are still able to regulate their FBG well. Hence, this study aimed to assess the utility of triglyceride-to-high-density lipoprotein cholesterol (TG : HDL-C) ratio as an IR marker in the modeling of pediatric MetS among children with obesity using structural equation modeling (SEM). A total of 524 blood samples from children with obesity (age 10-16 years old) were analyzed for FBG, lipids, insulin, leptin, and adiponectin. Both exploratory (EFA) and confirmatory factor analysis (CFA) were used to examine TG : HDL-C ratio as an IR marker in pediatric MetS. EFA shows that TG: HDL-C ratio (standardized factor loading = 0.904) groups together with homeostasis model assessment-estimated insulin resistance (HOMA-IR) (standardized factor loading = 0.664), indicating a strong correlation to the IR factor. Replacing FBG with TG: HDL-C ratio improved the modeling of MetS structure in children with obesity. Our MetS model of TG: HDL-C ratio as IR component shows comparable model fitness indices (goodness of fit, Akaike's information criterion, and Bayesian information criterion) with leptin:adiponectin ratio (platinum standard for adiposity:IR marker) model. The least model fit was seen when using FBG as an IR surrogate. TG : HDL-C ratio performed better as IR surrogate in MetS structures (standardized factor loading = 0.39) compared to FBG (standardized factor loading = 0.27). TG: HDL-C ratio may be considered as an IR component in pediatric MetS.

Food Liking-Based Diet Quality Indexes (DQI) Generated by Conceptual and Machine Learning Explained Variability in Cardiometabolic Risk Factors in Young Adults

The overall pattern of a diet (diet quality) is recognized as more important to health and chronic disease risk than single foods or food groups. Indexes of diet quality can be derived theoretically from evidence-based recommendations, empirically from existing datasets, or a combination of the two. We used these methods to derive diet quality indexes (DQI), generated from a novel dietary assessment, and to evaluate relationships with cardiometabolic risk factors in young adults with (n = 106) or without (n = 106) diagnosed depression (62% female, mean age = 21). Participants completed a liking survey (proxy for usual dietary consumption). Principle component analysis of plasma (insulin, glucose, lipids) and adiposity (BMI, Waist-to-Hip ratio) measures formed a continuous cardiometabolic risk factor score (CRFS). DQIs were created: theoretically (food/beverages grouped, weighted conceptually), empirically (grouping by factor analysis, weights empirically-derived by ridge regression analysis of CRFS), and hybrid (food/beverages conceptually-grouped, weights empirically-derived). The out-of-sample CRFS predictability for the DQI was assessed by two-fold and five-fold cross validations. While moderate consistencies between theoretically- and empirically-generated weights existed, the hybrid outperformed theoretical and empirical DQIs in cross validations (five-fold showed DQI explained 2.6% theoretical, 2.7% empirical, and 6.5% hybrid of CRFS variance). These pilot data support a liking survey that can generate reliable/valid DQIs that are significantly associated with cardiometabolic risk factors, especially theoretically- plus empirically-derived DQI.

Metabolic Syndrome Including Glycated Hemoglobin A1c in Adults: Is It Time to Change?

(1) Background: To assess the suitability of replacing conventional markers used for insulin resistance and dysglycemia by HbA1c in both the quantitative and qualitative metabolic syndrome (MetS) definition criteria; (2) Methods: Confirmatory factorial analysis was used to compare three quantitative definitions of MetS that consisted of many single-factor models, one of which included HbA1c as the dysglycemia indicator. After that, the model with the better goodness-of-fit was selected. Furthermore, a new MetS qualitative definition was proposed by replacing fasting plasma glucose with HbA1c > 5.7% in the International Diabetes Federation (IDF) definition. The clinical performance of these two MetS criteria (IDF and IDF-modified including HbA1c as the dysglycemia indicator) to predict vascular damage (pulse wave velocity [PWv], intima media thickness [IMT] and albumin-to-creatinine ratio [ACR]) was estimated; (3) Results: The single-factor model including HbA1c showed the better goodness-of-fit (χ² = 2.45, df = 2, p = 0.293, CFI = 0.999, SRMR = 0.010). Additionally, the IDF-modified criteria gained in clinical performance to predict vascular damage (diagnostic Odds Ratio: 6.94, 1.34 and 1.90) for pulse wave velocity (PWv), intima media thickness (IMT) and albumin-to-creatinine ratio (ACR), respectively; and (4) Conclusions: These data suggest that HbA1c could be considered as a useful component to be included in the MetS definition.

The polymorphic CAG repeat in exon 1 of androgen receptor is associated with level of HDL cholesterol and hypertension in Chinese middle-aged and elderly men

OBJECTIVE

The length of the CAG repeats in exon 1 of the androgen receptor (AR) gene has been shown to be inversely correlated with AR transcriptional activity. This study aimed to investigate the correlations between the length of CAG repeat in AR and serum lipids and hypertension in Chinese men.

DESIGN AND PATIENTS

The relationship between length of the CAG repeat in exon 1 of AR with prevalence of hypertension and the levels of serum lipids among Chinese men (aged ≥40 years).

MEASUREMENTS

The physical condition of the subjects was examined and recorded. The concentrations of blood lipids and sex hormones were measured, and the CAG repeat lengths of the AR gene were determined.

RESULTS

The length of the AR CAG repeats was associated with HDL cholesterol (HDL-C) concentration, and the stepwise multiple regression model showed that this association was independent of body mass index (BMI), triglycerides (TG) and total cholesterol (TC), although these factors influence HDL-C concentration. Furthermore, men with <22 vs men with ≥22 CAG repeats showed higher blood pressure and higher prevalence of hypertension. Shorter CAG repeat numbers were associated with the increased risk of hypertension in a multivariate logistic regression analysis (odds ratio = 0·715; 95% confidence interval, 0·517-0·989; P = 0·043). No significant correlation of AR CAG repeat polymorphism with sex hormone levels, TG, LDL cholesterol (LDL-C) or TC was found.

CONCLUSIONS

This study provides evidence that men carrying shorter (<22) AR CAG repeats have lower HDL-C level and increased risk of hypertension. The androgenic activity may differ due to the polymorphic length of CAG repeats of the AR gene.

Effects of Integrated Health Management Intervention on Overweight and Obesity

Overweight or obese adults aged 20~55 years and living in Beijing more than one year were randomly divided into different management groups. A one-year integrated health management intervention was applied in the health management groups. The physical indicators and metabolic indicators changed after one-year intervention on the overweight and obese adults. The annual reduction of the physical indicators was significant in all groups (p < 0.05) except the weight loss in the placebo + general management group. The health management and the dietary supplement have statistically significant (p < 0.001, p < 0.001) effects on the annual reduction of these indicators and interactive effect between them was found on some of these indicators such as bodyweight, body mass index (BMI), body fat ratio (BFR), and hipline (p < 0.05). The dietary supplement + health management group had the best annual reduction effects for the indicators among the groups. Integrated health management interventions including both dietary supplements intervention and health management could improve metabolic indicators in overweight and obese adults together with the physical indicators, suggesting the intermediated role of metabolic indictors in controlling obesity.

The factor structure of the metabolic syndrome in obese individuals with binge eating disorder

OBJECTIVE

Metabolic syndrome (MetS) is strongly linked with cardiovascular disease and type-II diabetes, but there has been debate over which metabolic measures constitute MetS. Obese individuals with binge eating disorder (BED) are one of the high risk populations for developing MetS due to their excess weight and maladaptive eating patterns, yet, the clustering patterns of metabolic measures have not been examined in this patient group.

METHODS

347 adults (71.8% women) were recruited for treatment studies for obese individuals with BED. We used the VARCLUS procedure in the Statistical Analysis System (SAS) to investigate the clustering pattern of metabolic risk measures.

RESULTS

The analysis yielded four factors: obesity (body-mass-index [BMI] and waist circumference), lipids (HDL and triglycerides), blood pressure (systolic and diastolic blood pressure), and glucose regulation (fasting serum glucose and Hb1Ac). The four factors accounted for 84% of the total variances, and variances explained by each factor were not substantially different. There was no inter-correlation between the four factors. Subgroup analyses by sex and by race (Caucasian vs. African American) yielded the same four-factor structure.

CONCLUSION

The factor structure of MetS in obese individuals with BED is not different from those found in normative population studies. This factor structure may be applicable to the diverse population.

educational level, obesity and incidence of diabetes among Chinese adult men and women aged 18-59 years old: an 11-year follow-up study

OBJECTIVE

To determine whether educational level and overweight/obesity was associated with the development of diabetes among Chinese adult men and women.

METHODS

A cohort (2000-2011) of 10 704 participants aged 18-59 years (8 238 men, 2 466 women) in Qingdao Port Health Study (QPHS) were recruited in this study. The personal lifestyle, height, weight, waist circumference, resting heart rate, blood pressure, fasting blood glucose, total cholesterol, triglycerides and plasma uric acid were collected annually in a comprehensive health checkup program. Cox proportional hazards regression models were used to estimate the association of factors and incidence of diabetes.

RESULTS

During 110 825 person-years of follow-up, 1 056 new onset cases (9.5 per 1 000 person-years) of diabetes were identified. With normal weight as reference, the multiple-adjusted hazard ratio (HR) (95%CI) of diabetes was 1.69(1.38-2.09) for overweight and 2.24(1.66-3.02) for obesity among men, which was 1.81(1.12-2.92) and 2.58(1.37-4.86) among women, respectively. Compared with the participants with high educational level, those with low educational level had a higher risk of diabetes (multiple-adjusted HR (95%CI): 1.43(1.11-1.86)) among men. The association was not found among women and the adjusted HR (95%CI) of diabetes was 1.56(0.89-2.76). The increased risks of low educational level were independent of mediators among men, through normal weight (P for trend = 0.0313) and overweight (P for trend = 0.0212) group but not obesity group (P for trend = 0.0957).

CONCLUSION

Baseline overweight/obesity was an independent risk factor for diabetes for both men and women. Low educational level was adversely associated with incidence of diabetes through normal weight, overweight and obesity groups, with the association being substantially attenuated by mediating factors only in the obesity group among men. The association was not found among women.

The structure of metabolic syndrome components across follow-up survey from childhood to adolescence

BACKGROUND

The choice of what parameters are needed for the diagnosis of Metabolic syndrome (MetS) has been criticized due to the lack of an actual "gold standard" diagnostic test even in adults. This problem seems to be greater in children and adolescents.

OBJECTIVES

Stability assessment of factor structure underlying metabolic syndrome (MetS) components from childhood to adolescence in a panel study.

PATIENTS AND METHODS

A total number of 643 (305 boys and 338 girls) children (from 1999 to 2001), aged 6-10 years, with a complete median follow-up of 6.7 years (from 2006 to 2008) were selected among participants of Tehran Lipid and Glucose Study. We proposed 6 measured variables based on risk factors defined in Adult Treatment Panel III guidelines to describe clustering of MetS components.

RESULTS

The Goodness of fit of the two-factor model, extracted from exploratory factor analysis, was appropriate for boys and girls in both stages of the study using confirmatory factor analysis. Systolic blood pressure (SBP) and triglycerides (TGs), with parameter estimates (PE) of 1 and 0.75, respectively, were the greatest risk factors at baseline in boys and girls. Waist circumference with PE of 0.88 and 0.62, and SBP with PE of 0.99 and 0.86 in adolescent boys and girls, respectively, were important risk factors.

CONCLUSIONS

Our panel study supports the stability of the two-factor six-variable model across two developmental stages from childhood to adolescence, among which adiposity, SBP, and TG were the predominant risk factors.

Ambulatory blood pressure and the metabolic syndrome in normotensive and untreated hypertensive men

BACKGROUND

Components of the metabolic syndrome are typically intercorrelated in epidemiologic studies and, when combined, predict type 2 diabetes and cardiovascular diseases. However, it remains unclear whether a single construct underlies the various components and which of the components are most closely associated with the underlying syndrome. Here, we use our confirmatory factor analytic model of the metabolic syndrome to examine the extent to which measures of ambulatory blood pressure, reflecting blood pressure variability throughout the day and night, may strengthen the association between blood pressure and the other components of the syndrome.

METHODS

Participants were a community sample of 358 men (248 with hypertension), ages 40-70, not receiving antihypertensive medications. Confirmatory factor analysis was employed to examine model fit and the strength of association between clinic and ambulatory blood pressure and the metabolic syndrome.

RESULTS

The blood pressure factor loaded significantly on the underlying metabolic syndrome but the strength of association was not as great (loading = 0.34, p < 0.01) as those observed for the obesity, insulin resistance and lipid factors. The factor loadings for the ambulatory measures (awake loading = 0.19; sleep loading = 0.16, p values < 0.01) were significant but smaller in magnitude than the loadings for clinic blood pressure.

CONCLUSIONS

Both clinic and ambulatory measures of blood pressure are significantly associated with the underlying metabolic syndrome using confirmatory factor analytic methods. However, the strength of association appears greater for the clinic measures relative to the ambulatory measures in this study.

Factor analysis of modifiable cardiovascular risk factors and prevalence of metabolic syndrome in adult Taiwanese

To assess the clustering of modifiable cardiovascular risk factors among Taiwanese adults, we evaluated 579 healthy participants who underwent health examinations between May and December 2007. Exploratory factor analysis was used to examine risk factor clustering. Smoking, alcohol intake, exercise habits, body mass index, waist circumference, total cholesterol, triglycerides, high- and low-density lipoprotein cholesterol, fasting glucose, uric acid, serum hepatic enzymes, and mean arterial pressure were assessed. Separate factor analyses assessed total and low-density lipoprotein cholesterol. Principal components analysis identified five factors for a model without low-density lipoprotein cholesterol and four factors for a model without total cholesterol. Four common factors in both models explained between 51.1 and 51.8% of variance in the original 14 factors. Metabolic factors, hematological factors (white blood cells and platelets), lifestyle factors (smoking and alcohol consumption), and exercise habits and fasting blood glucose explained about 20, 11, 10, 10% of total variance, respectively. In the model without low-density lipoprotein cholesterol, total cholesterol factor explained 8.83% of variance. This study confirmed clustering of established metabolic syndrome components and revealed additional associated cardiovascular disease risk factors, including lifestyle factors, exercise and total cholesterol, which should be targeted in prevention efforts.

A systematic evaluation of the insulin resistance syndrome as an independent risk factor for cardiovascular disease mortality and derivation of a clinical index

Insulin resistance-related risk factor clustering (the insulin resistance syndrome or IRS) may be a cardiovascular disease (CVD) risk factor, but a convincing demonstration of this requires a rigorously derived reference measure and a systematic evaluation of measures and indices that derive from that measure. Using established IRS characteristics, factor analysis in 832 white men, generally healthy at baseline, generated a priori an IRS reference measure. An IRS diagnostic was chosen by evaluating CVD mortality risk in percentiles of the reference measure. An IRS clinical index was derived by (1) identification of readily measured, independent predictors of the IRS reference measure by multiple linear regression; (2) assignment to each predictor of a cut point optimal for discrimination of participants diagnosed with IRS; and (3) selection of a combination of the dichotomized predictors that further optimized IRS discrimination. The reference IRS diagnostic was defined by the top 16.7% of the IRS reference measure and predicted CVD mortality in Cox proportional hazards modeling (hazard ratio, 2.7; 95% confidence interval, 1.5-5.2; P = .002). An optimized IRS index was defined by triglycerides of at least 1.6 mmol/L and uric acid of at least 400 μmol/L plus any one of fasting plasma glucose of at least 5.4 mmol/L, diastolic blood pressure of at least 90 mm Hg, or body mass index of at least 27.0 kg/m(2) and predicted CVD mortality (hazard ratio, 2.14 [1.08-4.24]; P = .02). Prediction was independent of hypertension, hypercholesterolemia, and smoking. Conventionally derived glucoregulatory insulin resistance and metabolic syndrome were not predictive. The IRS is an independent risk factor for CVD mortality; and an effective, clinically usable index can be derived from readily measured variables.

Triglycerides and triglycerides to high-density lipoprotein cholesterol ratio are strong predictors of incident hypertension in Middle Eastern women

Dyslipidemia has been reported as a risk factor for incident hypertension in a few prospective studies, however, no study has specifically assessed different lipid measures including the lipid ratios, that is, total cholesterol (TC)/high-density lipoprotein cholesterol (HDL-C) and triglycerides (TGs)/HDL-C as predictors of hypertension among Middle Eastern women with high prevalences of dyslipidemia and hypertension. The study population consisted of 2831 non-hypertensive women, aged ≥ 20 years. We measured lipoproteins, and calculated non-HDL-C and the lipid ratios. The risk-factor-adjusted odds ratios for incident hypertension were calculated for every 1 standard deviation (s.d.) change in TC, log-transformed TG, HDL-C, non-HDL-C, TC/HDL-C and log-transformed TG/HDL-C using multivariate logistic regression analysis. Over a mean follow-up of 6.4 years, 397 women developed hypertension. An increase of 1 s.d. in TG, TC/HDL-C and TG/HDL-C increased the risk of incident hypertension by 16, 19 and 18%, respectively, and 1 s.d. increase in HDL-C decreased the risk of hypertension by 14% in the multivariable model (all P ≤ 0.05). In models excluding women with diabetes and central or general obesity, TG, TG/HDL-C and TC/HDL-C remained as independent predictors of incident hypertension. In conclusion, dyslipidemia, using serum TG and TG/HDL-C, in particular, may be useful in identification of women at risk of hypertension, even in those without diabetes and central or general obesity.

Simple indices of inflammation as predictors of death from cancer or cardiovascular disease in a prospective cohort after two decades of follow-up

BACKGROUND

Previous studies have identified sub-clinical inflammation as a potential factor in the pathogenesis of cancer and cardiovascular disease (CVD) but the possibility that simple, readily measured indices of sub-clinical inflammation might predict both CVD and cancer has not been tested in the context of a single, prospective analysis.

AIM

To evaluate simply measured indices of inflammation as long-term predictors of death from either cancer or CVD.

DESIGN

Prospective open cohort study.

METHODS

A total of 1192 white males received measurements of a range of risk markers including the inflammation indices white blood cell count (WBC), erythrocyte sedimentation rate (ESR) and serum globulin concentrations. Inflammation marker clustering was quantified as a factor-analysis-derived inflammation score and survival time to death from any cancer or CVD was modeled on baseline measures using the Cox proportional hazards model.

RESULTS

A total of 1010 participants met inclusion criteria, of whom 94 died of cancer and 67 of CVD. Mean follow-up times among cases and survivors ranged from 18.2-21.9 years. Independently of established risk factors [age, body mass index (BMI), smoking, alcohol and exercise], WBC, ESR and globulin levels were all individually predictive of both cancer (hazard ratio 1.43, P = 0.002; 1.27, P = 0.02; 1.26, P = 0.02, respectively) and CVD mortality (1.29, P = 0.06; 1.43, P = 0.007; 1.50, P = 0.001). The inflammation score predicted both cancer mortality (1.35, P = 0.003) and CVD mortality (1.46, P = 0.002). Risks associated with high inflammation score were equivalent to and independent of smoking cigarettes for cancer or, for CVD, having a serum cholesterol concentration ≥6.2 mmol/l.

CONCLUSIONS

Simple indices of inflammation predict death from cancer or CVD two decades later as strongly as smoking predicts cancer or cholesterol predicts CVD. Their measurement could contribute to evaluation of both cancer and CVD risk.

Sex differences in environmental and genetic factors for hypertension

BACKGROUND

Sex differences are observed in many aspects of mammalian cardiovascular function and pathology. Hypertension is more common in men than in women of the same age. Although the effects of gonadal hormones on blood pressure are considered contributing factors, the reasons for sex differences in hypertension are still not fully understood. The present study was undertaken to compare the differences in several environmental and genetic factors between men and women in the Hei Yi Zhuang, an isolated subgroup of the Zhuang minority in China.

METHODS

Information on demography, diet, and lifestyle was collected in 835 women and 834 men aged 15 to 84 years. Genotyping of angiotensin-converting enzyme, adrenergic receptor beta(3), aldehyde dehydrogenase 2, calpastatin, connexin 37, hepatic lipase, lipoprotein lipase, peroxisome proliferator-activated receptor gamma, thyrotropin-releasing hormone receptor, and von Willebrand factor also was performed in these subjects.

RESULTS

The levels of systolic and diastolic blood pressure, and the prevalence, awareness, and treatment of hypertension were lower in women than in men (P < .05). Hypertension was positively associated with age, physical activity, alcohol consumption, body mass index, waist circumference, hyperlipidemia, total energy, total fat, sodium intake, and sodium/potassium ratio, and negatively associated with education level, total dietary fiber, potassium intake, angiotensin-converting enzyme, aldehyde dehydrogenase 2, and hepatic lipase genotypes in men (P < .05). Hypertension was positively associated with age, hyperlipidemia, total energy, total fat, sodium intake, sodium/potassium ratio, calpastatin, and von Willebrand factor genotypes, and negatively associated with education level, total dietary fiber, potassium, calcium intake, lipoprotein lipase, and thyrotropin-releasing hormone receptor genotypes in women (P < .05).

CONCLUSION

Sex differences in the prevalence of hypertension in the Hei Yi Zhuang population may be mainly attributed to the differences in dietary habits, lifestyle choices, sodium and potassium intakes, physical activity level, and some genetic polymorphisms.

Co-associations between insulin sensitivity and measures of liver function, subclinical inflammation, and hematology

Clustering of risk factors for coronary heart disease and diabetes is well established, particularly in relation to insulin resistance. To determine whether evaluation of risk factor clustering will contribute to risk assessment, it is first necessary to discriminate co-association between risk factors from correlation. We undertook this in a large homogenous group, using a sophisticated measure of insulin sensitivity and a broad range of risk factors. Cross-sectional analysis of an occupational cohort using regression and factor analyses was performed. Subjects were 472 apparently healthy white men. The main outcome measures were insulin sensitivity, S(I), by minimal model analysis of the intravenous glucose tolerance test plus liver function and hematologic variables, including the inflammation indices, leukocyte count, and erythrocyte sedimentation rate. The S(I) correlated independently with serum gamma-glutamyl transferase (GGT), aspartate transaminase, and alkaline phosphatase activities; blood pressure; leukocyte count; and erythrocyte sedimentation rate (P < .01). On factor analysis, the factor that explained the greatest proportion of the variance (56.7%) included, in decreasing order of factor loading, triglycerides, S(I) (negative), body mass index, high-density lipoprotein cholesterol (negative), insulin, uric acid, and GGT activity (loadings >0.40). Mean arterial pressure was not a feature (loading 0.29), neither were indices of subclinical inflammation. In apparently healthy men, blood pressure and indices of subclinical inflammation do not cluster with other insulin resistance-related risk factors, despite correlating with insulin sensitivity. In contrast, both GGT activity and uric acid concentrations correlated with insulin sensitivity and co-associated with insulin resistance-related risk factors and are therefore components of a true risk factor cluster.

Genome-wide linkage scan for the metabolic syndrome: the GENNID study

In the United States, the metabolic syndrome (MetS) constitutes a major public health problem with over 47 million persons meeting clinical criteria for MetS. Numerous studies have suggested genetic susceptibility to MetS. The goals of this study were (i) to identify susceptibility loci for MetS in well-characterized families with type 2 diabetes (T2D) in four ethnic groups and (ii) to determine whether evidence for linkage varies across the four groups. The GENNID study (Genetics of NIDDM) is a multicenter study established by the American Diabetes Association in 1993 and comprises a comprehensive, well-characterized resource of T2D families from four ethnic groups (whites, Mexican Americans, African Americans, and Japanese Americans). Principal component factor analysis (PCFA) was used to define quantitative phenotypes of the MetS. Variance components linkage analysis was conducted using microsatellite markers from a 10-cM genome-wide linkage scan, separately in each of the four ethnic groups. Three quantitative MetS factors were identified by PCFA and used as phenotypes for MetS: (i) a weight/waist factor, (ii) a blood pressure factor, and (iii) a lipid factor. Evidence for linkage to each of these factors was observed. For each ethnic group, our results suggest that several regions harbor susceptibility genes for the MetS. The strongest evidence for linkage for MetS phenotypes was observed on chromosome 2 (2q12.1-2q13) in the white sample and on chromosome 3 (3q26.1-3q29) in the Mexican-American sample. In conclusion, the results suggest that several regions harbor MetS susceptibility genes and that heterogeneity may exist across groups.

Effects of febuxostat on metabolic and renal alterations in rats with fructose-induced metabolic syndrome

Increased fructose consumption is associated with hyperuricemia, metabolic syndrome, and renal damage. This study evaluated whether febuxostat (Fx), an investigational nonpurine, and selective xanthine oxidase inhibitor, could alleviate the features of metabolic syndrome as well as the renal hemodynamic alterations and afferent arteriolopathy induced by a high-fructose diet in rats. Two groups of rats were fed a high-fructose diet (60% fructose) for 8 wk, and two groups received a normal diet. For each diet, one group was treated with Fx (5-6 mg.kg(-1).day(-1) in the drinking water) during the last 4 wk (i.e., after the onset of metabolic syndrome), and the other received no treatment (placebo; P). Body weight was measured daily. Systolic blood pressure and fasting plasma uric acid (UA), insulin, and triglycerides were measured at baseline and at 4 and 8 wk. Renal hemodynamics and histomorphology were evaluated at the end of the study. A high-fructose diet was associated with hyperuricemia, hypertension, as well as increased plasma triglycerides and insulin. Compared with fructose+P, fructose+Fx rats showed significantly lowered blood pressure, UA, triglycerides, and insulin (P < 0.05 for all comparisons). Moreover, fructose+Fx rats had significantly reduced glomerular pressure, renal vasoconstriction, and afferent arteriolar area relative to fructose+P rats. Fx treatment in rats on a normal diet had no significant effects. In conclusion, normalization of plasma UA with Fx in rats with metabolic syndrome alleviated both metabolic and glomerular hemodynamic and morphological alterations. These results provide further evidence for a pathogenic role of hyperuricemia in fructose-mediated metabolic syndrome.

Elevated serum uric acid levels in metabolic syndrome: an active component or an innocent bystander?

Elevated serum uric acid (SUA) levels are commonly seen in patients with the metabolic syndrome (MetS). Several mechanisms, both direct and indirect, connect the increased SUA levels with the established diagnostic criteria of MetS. It is possible that the increased cardiovascular disease risk associated with the MetS is partially attributed to elevated circulating SUA concentration. Several drugs used in the treatment of MetS may alter SUA levels. Thus, lifestyle measures together with the judicious selection of drugs for the treatment of hypertension, dyslipidemia, and insulin resistance associated with MetS may result in a reduction of SUA levels and possibly cardiovascular disease risk. This review summarizes the pathophysiologic association between SUA and MetS and focuses on the prevention of hyperuricemia and its cardiovascular consequences.

Is hyperuricemia another facet of the metabolic syndrome?

BACKGROUND

Hyperuricemia is commonly associated with obesity, glucose intolerance, hypertension, dyslipidemia, and atherosclerotic cardiovascular disease. The resemblance of the metabolic syndrome and hyperuricemia has led to the suggestion that hyperuricemia is a part of the metabolic syndrome. The purpose of this study is to examine the contribution of uric acid (UA) as an additional component of the metabolic syndrome in middle-aged men.

METHODS

In total, 393 male participants, aged 45-60 years, were recruited from a professional health evaluation program. Anthropometric measurements and blood pressure (BP) were taken after an overnight fast. Fasting blood samples were collected for the measurements of glucose, UA, and lipid profile. Logistic regression models were fitted to examine the relationship between UA and the diagnosis of metabolic syndrome. Factor analysis was performed to explore the relationship between UA and the components of the metabolic syndrome.

RESULTS

The diagnosis of the metabolic syndrome was significantly associated with waist circumference (WC), glucose, triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), systolic BP, and liver enzyme levels, but not associated with UA levels. The sensitivity of hyperuricemia (serum UA > or = 7.0 mg/dL) for the diagnosis of the metabolic syndrome was 58.0% and the specificity was 55.3%. In factor analysis, UA aggregated with body mass index, WC, glucose, log TG, and HDL-C as a metabolic factor. Systolic and diastolic BP were loaded on a second factor separately. The model loaded with UA explained a similar proportion of the total variance (56.9%), as did the model loaded without UA (62.5%).

CONCLUSION

Our results suggest that the contribution of UA as an additional component of the syndrome seems to be insignificant. We propose that hyperuricemia might not be an important facet for the understanding of the underlying structure of the metabolic syndrome.

Clustering of haemostatic variables and the effect of high cashew and walnut diets on these variables in metabolic syndrome patients

We investigated the effect of a high walnut and cashew diet on haemostatic variables in people with the metabolic syndrome. Factor analysis was used to determine how the haemostatic variables cluster with other components of the metabolic syndrome and multiple regression to determine possible predictors. This randomized, control, parallel, controlled-feeding trial included 68 subjects who complied with the Third National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol criteria. After a 3-week run-in following the control diet, subjects were divided into three groups receiving either walnuts or cashews (20 energy%) or a control diet for 8 weeks. The nut intervention had no significant effect on von Willebrand factor antigen, fibrinogen, factor VII coagulant activity, plasminogen activator inhibitor 1 activity, tissue plasminogen activator activity or thrombin activatable fibrinolysis inhibitor. Statistically, fibrinogen clustered with the body-mass-correlates and acute phase response factors, and factor VII coagulant activity clustered with high-density lipoprotein cholesterol (HDL-C). Tissue plasminogen activator activity, plasminogen activator inhibitor 1 activity and von Willebrand factor antigen clustered into a separate endothelial function factor. HDL-C and markers of obesity were the strongest predictors of the haemostatic variables. We conclude that high walnut and cashew diets did not influence haemostatic factors in this group of metabolic syndrome subjects. The HDL-C increase and weight loss may be the main focus of dietary intervention for the metabolic syndrome. Furthermore, diet composition may have only limited effects if weight loss is not achieved.

Is the factor structure of the metabolic syndrome comparable between men and women and across three ethnic groups: the Miami Community Health Study

PURPOSE

The metabolic syndrome (MS) is conceived as a cluster of disorders that increase risk for coronary heart disease and type 2 diabetes. Studies examining its structure primarily have used an exploratory factor analytic technique, but yielded discrepant results. There also is a lack of research that investigates whether the clustering pattern is similar across sex and ethnic groups. This study uses confirmatory factor analysis to evaluate the factor structure of the MS and examines its similarity between men and women and across three ethnic groups (Caucasian, African, and Cuban Americans).

METHOD

A hierarchical four-factor model with an overarching MS factor uniting insulin resistance, obesity, lipid, and blood pressure factors was tested with 517 individuals from the Miami Community Health Study.

RESULTS

Findings show that the proposed structure was well supported (comparative fit index=0.97) and similar between men and women and across ethnic groups. The MS was represented strongly by insulin resistance, followed by obesity, lipid factors, and, to a lesser extent, a blood pressure factor.

CONCLUSIONS

This study provides empirical support for identifying and diagnosing the MS by its component factors in a diverse population.

Less than 50% of variation in HDL cholesterol between and within individuals, is explained by established predictors

Variation in serum high density lipoprotein cholesterol (HDL-C) concentrations is believed to be largely explained by triglycerides, but this has been mainly explored in cross-sectional analyses. Eight hundred and eighty one white male participants in a health screening program attended on a total of 2158 occasions for measurements that included fasting HDL-C, low density lipoprotein cholesterol (LDL-C) and homeostasis model assessment insulin resistance (HOMA-R). Baseline, change between-visit and repeated-measures regression models were used to analyse predictors of between- and within-individual variation in HDL-C. Independent predictors of between-individual variation included serum triglycerides (20.3 or 19.6% of the variance explained, depending on the model used), body mass index (BMI: 4.7 and 4.3%), cigarette smoking (3.3 and 1.5%) and alcohol consumption (0.4 and 1.1%). Within-individual variation in HDL-C was explained by changes in serum triglycerides (4.7 and 7.5%) and BMI (5.3 and 2.9%). In multivariate models, 24.3 and 24.9% of between-individual variation in HDL-C, and 7.9 and 8.8% of within-individual variation could be explained, depending on the model used. Sixty percent of the variation in HDL-C was due to unobserved factors. The majority of variation in HDL-C remains to be explained by influences other than the conventional variables: triglyceride and LDL cholesterol concentrations, insulin resistance, smoking and alcohol.

An evaluation of the metabolic syndrome in the HyperGEN study

BACKGROUND: In 2001 the National Cholesterol Education Program (NCEP) provided a categorical definition for metabolic syndrome (c-MetS). We studied the extent to which two ethnic groups, Blacks and Whites were affected by c-MetS. The groups were members of the Hypertension Genetic Epidemiology Network (HyperGEN), a part of the Family Blood Pressure Program, supported by the NHLBI. Although the c-MetS definition is of special interest in particular to the clinicians, the quantitative latent traits of the metabolic syndrome (MetS) are also important in order to gain further understanding of its etiology. In this study, quantitative evaluation of the MetS latent traits (q-MetS) was based on the statistical multivariate method factor analysis (FA). RESULTS: The prevalence of the c-MetS was 34% in Blacks and 39% in Whites. c-MetS showed predominance of obesity, hypertension, and dyslipidemia. Three and four factor domains were identified through FA, classified as "Obesity," "Blood pressure," "Lipids," and "Central obesity." They explained approximately 60% of the variance in the 11 original variables. Two factors classified as "Obesity" and "Central Obesity" overlapped when FA was performed without rotation. All four factors in FA with Varimax rotation were consistent between Blacks and Whites, between genders and also after excluding type 2 diabetes (T2D) participants. Fasting insulin (INS) associated mainly with obesity and lipids factors. CONCLUSIONS: MetS in the HyperGEN study has a compound phenotype with separate domains for obesity, blood pressure, and lipids. Obesity and its relationship to lipids and insulin is clearly the dominant factor in MetS. Linkage analysis on factor scores for components of MetS, in familial studies such as HyperGEN, can assist in understanding the genetic pathways for MetS and their interactions with the environment, as a first step in identifying the underlying pathophysiological causes of this syndrome.

Hemostatic risk factors and insulin sensitivity, regional body fat distribution, and the metabolic syndrome

Disturbances in the thrombotic and fibrinolytic systems are a feature of insulin resistance, obesity, and the metabolic syndrome. However, there are few studies in which these relationships have been explored in mainly asymptomatic individuals using sophisticated measures of insulin sensitivity and regional adiposity. Variables of the hemostatic system were measured in 106 men (aged 32-68 yr; body mass index, 20-34 kg/m(2)). Insulin sensitivity was measured by minimal model analysis and regional adiposity by dual energy x-ray absorptiometry. Clustering of intercorrelated variables was assessed by the statistical technique of factor analysis. Plasma levels of procoagulant factors VII and X, anticoagulant proteins C and S, and plasminogen activator inhibitor-1 correlated positively with total and percent central body fat (r = 0.25-0.38; P < 0.05) and negatively with insulin sensitivity (except protein S; r = -0.24 to -0.35; P < 0.05). On factor analysis, procoagulant factors VII and X, proteins C and S, and plasminogen activator inhibitor-1 were components of the cluster of variables that explained the greatest proportion of the variance in the data (39.2%). Other variables included in this cluster were those typical of the metabolic syndrome and also serum gamma-glutamyl transferase activity. These results suggest that factors VII and X and proteins C and S are features of the intercorrelated disturbances of the metabolic syndrome. Associations with adiposity and liver enzyme activity suggest the involvement of hepatic fat deposition.

Inflammation markers and erythrocyte sedimentation rate but not metabolic syndrome factor score predict coronary heart disease in high socioeconomic class males: the HDDRISC study

OBJECTIVE

To evaluate prediction of coronary heart disease (CHD) by quantitative measures of the metabolic syndrome and inflammation in a cohort of high socio-economic status males.

METHODS

Incident CHD was identified in a cohort of 649 male participants in a company health programme during a mean follow-up of 10.6 years. Using factor analysis, metabolic syndrome and sub-clinical inflammation scores were derived from baseline measurements, which included an oral glucose tolerance test-derived measure of insulin resistance. Factor scores were then included as predictor variables in a Cox regression analysis of incident CHD.

RESULTS

Forty-two cases of definite CHD were identified on follow-up. The conventional risk factors, cigarette smoking, blood pressure, total cholesterol and low HDL cholesterol were clearly distinguished as significant predictors of incident CHD. Erythrocyte sedimentation rate was also an independent predictor (coefficient 0.0480, z score 2.39, p=0.017). The metabolic syndrome factor included insulin resistance, body mass index, serum triglycerides, glucose tolerance, serum uric acid and fasting plasma glucose. The inflammation factor included serum globulin, blood leukocyte count, low albumin, haemoglobin and cholesterol, but not erythrocyte sedimentation rate. The inflammation factor score was a significant predictor of CHD (coefficient 0.4601, z score 2.43, p=0.015) but the metabolic syndrome factor was not (coefficient 0.2488, z score 1.24, p=0.2).

CONCLUSIONS

Erythrocyte sedimentation rate and a factor analysis-derived measure of sub-clinical inflammation were important in the development of CHD in this relatively low-risk group, but neither metabolic syndrome factor score nor its individual components predicted CHD.

Depressive symptoms and metabolic risk in adult male twins enrolled in the National Heart, Lung, and Blood Institute twin study

OBJECTIVE

To determine the extent to which depressive symptoms are associated with metabolic risk factors and whether genetic or environmental factors account for this association.

METHOD

Twin structural equation modeling was employed to estimate genetic and environmental contributions to the covariation of depressive symptoms, as indexed by the Centers for Epidemiological Studies-Depression Scale, and common variance among blood pressure, body mass index, waist-to-hip ratio, and serum triglycerides and glucose among 87 monozygotic and 86 dizygotic male twin pairs who participated in the NHLBI twin study.

RESULTS

Depressive symptoms were associated with individual components of the metabolic syndrome and common variance among the risk factors. Twin structural equation modeling indicated that the associations were attributable to environmental (nongenetic) factors.

CONCLUSIONS

These results support the hypothesis that depressive symptoms may increase risk for a pattern of physiological risk consistent with the metabolic syndrome.

The role of insulin resistance in the pathogenesis of Alzheimer's disease: implications for treatment

An emerging body of evidence suggests that an increased prevalence of insulin abnormalities and insulin resistance in Alzheimer's disease may contribute to the disease pathophysiology and clinical symptoms. It has long been known that insulin is essential for energy metabolism in the periphery. In the past 2 decades, convergent findings have begun to demonstrate that insulin also plays a role in energy metabolism and other aspects of CNS function. Investigators reported 20 years ago that insulin and insulin receptors were densely but selectively expressed in the brain, including the medial temporal regions that support the formation of memory. It has recently been demonstrated that insulin-sensitive glucose transporters are localised to the same regions supporting memory and that insulin plays a role in memory functions. Collectively, these findings suggest that insulin may contribute to normal cognitive functioning and that insulin abnormalities may exacerbate cognitive impairments, such as those associated with Alzheimer's disease. Insulin may also play a role in regulating the amyloid precursor protein and its derivative beta-amyloid (Abeta), which is associated with senile plaques, a neuropathological hallmark of Alzheimer's disease. It has been proposed that insulin can accelerate the intracellular trafficking of Abeta and interfere with its degradation. These findings are consistent with the notion that insulin abnormalities may potentially influence levels of Abeta in the brains of patients with Alzheimer's disease. The increased occurrence of insulin resistance in Alzheimer's disease and the numerous mechanisms through which insulin may affect clinical and pathological aspects of the disease suggest that improving insulin effectiveness may have therapeutic benefit for patients with Alzheimer's disease. The thiazolidinedione rosiglitazone has been shown to have a potent insulin-sensitising action that appears to be mediated through the peroxisome proliferator-activated receptor-gamma (PPAR-gamma). PPAR-gamma agonists, such as rosiglitazone, also have anti-inflammatory effects that may be of therapeutic benefit in patients with Alzheimer's disease. This review presents evidence suggesting that insulin resistance plays a role in the pathophysiology and clinical symptoms of Alzheimer's disease. Based on this evidence, we propose that treatment of insulin resistance may reduce the risk or retard the development of Alzheimer's disease.

Risk factor clustering in the insulin resistance syndrome and its relationship to cardiovascular disease in postmenopausal white, black, hispanic, and Asian/Pacific Islander women

The aim of this study was to examine how major components of the insulin resistance (IR) syndrome relate to each other and to cardiovascular disease (CVD) in postmenopausal women in 4 ethnic groups. Baseline data from the Women's Health Initiative (WHI) on 3,083 50- to 79-year-old women (1,635 white, 802 black, 390 Hispanic, and 256 Asian/Pacific Islander) were examined. Participants underwent a personal interview and a physical examination, blood samples were drawn, and a detailed cardiovascular history was ascertained. Factor analysis was used to assess the clustering and interdependence of groups of CVD-related IR syndrome variables. Four factors were identified. An obesity factor included IR in all groups and had a significant association with CVD in white (P =.0001) and Hispanic (P =.0024) women. A dyslipidemia factor (high-density lipoprotein [HDL], triglycerides, and HDL2: total HDL ratio) also included insulin and IR and was significantly correlated with CVD in black (P=.0006) and Hispanic (P =.0217) women and had a borderline association in white women (P =.068). Total and low-density lipoprotein (LDL) cholesterol did not relate to CVD in any group. Blood pressure was related weakly to CVD in white women (P =.0434) and strongly in black women (P =.0095). Components of the IR syndrome appear to be associated with CVD in postmenopausal women, although the magnitude of these relationships differed by ethnicity.

Components of the "metabolic syndrome" and incidence of type 2 diabetes

The combination of insulin resistance, dyslipidemia, hypertension, and obesity has been described as a "metabolic syndrome" that is a strong determinant of type 2 diabetes. Factor analysis was used to identify components of this syndrome in 1,918 Pima Indians. Prospective analyses were conducted to evaluate associations of identified factors with incidence of diabetes. Factor analysis identified 4 factors that accounted for 79% of the variance in the original 10 variables. Each of these factors reflected a proposed component of the metabolic syndrome: insulinemia, body size, blood pressure, and lipid metabolism. Among 890 originally nondiabetic participants with follow-up data, 144 developed diabetes in a median follow-up of 4.1 years. The insulinemia factor was strongly associated with diabetes incidence (incidence rate ratio [IRR] for a 1-SD difference in factor scores = 1.81, P < 0.01). The body size and lipids factors also significantly predicted diabetes (IRR 1.52 and 1.37, respectively, P < 0.01 for both), whereas the blood pressure factor did not (IRR 1.11, P = 0.20). Identification of four unique factors with different associations with incidence of diabetes suggests that the correlations among these variables reflect distinct metabolic processes, about which substantial information may be lost in the attempt to combine them into a single entity.

Factor analysis of ethnic variation in the multiple metabolic (insulin resistance) syndrome in three Canadian populations

This study describes and compares the pattern of risk factor clustering in multiple metabolic (insulin resistance) syndrome (MMS) in three Canadian ethnic groups (Indians, Inuit, non-Aboriginal Canadians). Three cross-sectional, population-based sample surveys in three contiguous regions of Canada were conducted during the late 1980s and early 1990s (Ontario, Manitoba, Northwest Territories). The combined dataset consists of 873 Cree-Ojibwa Indians from northern Ontario and Manitoba, 387 Inuit from the Northwest Territories, and 2,670 non-Aboriginal Canadians (predominantly of European origin) in the province of Manitoba. The samples are representative of the noninstitutionalized, adult population of their respective catchment areas. Factor analysis transformed 10 anthropometric and metabolic variables into three uncorrelated factors. Three factors, which together account for 64.3% of the variance, can be identified: an "obesity factor" (factor loadings for weight, height, waist and hip girth, and HDL-cholesterol); a "blood pressure factor" (factor loadings for mean systolic and diastolic BP and total cholesterol); and a "lipid/glucose factor" (factor loadings for triglycerides, total cholesterol, HDL, and fasting plasma glucose). Fasting insulin is available for only a subset of the data and separate analysis shows that it groups with glucose. Factor scores generated by the factor analysis differ according to ethnic group, diabetes status, and sex on multivariate analysis of variance. Indians have the highest scores for all three factors. Inuit have the lowest obesity scores and are not significantly different from non-Aboriginal people with regard to the other two factors. MMS is prevalent in diverse ethnic groups but varies in the pattern of phenotypic expression, with some components more prominent in some groups.

Insulin resistance syndrome revisited: application of self-organizing maps

BACKGROUND

Most common chronic diseases have a multifaceted aetiological background. Because currently used statistical methods have severe limitations in describing complex non-linear processes, the authors evaluated the usefulness of a multivariate method which is able to describe non-linear phenomena, the self-organizing map (SOM).

METHODS

The study subjects were the 1650 participants of the Kuopio Ischemic Heart Disease Risk Factor Study (KIHD). The SOM model was constructed using 25 continuous biochemical and physiological variables. The aim of the SOM algorithm, together with Sammon's mapping, is to group the data into reduced but representative format and divide the study population into homogeneous subgroups.

RESULTS

The study population consisted of four groups (clusters) according to the method used. In the clusters C1 to C4 were 637, 445, 275 and 121 men, respectively. There were eight neurons (n = 172) which were not included to the four main clusters. The mean values of the variables related to insulin resistance syndrome in the identified SOM map were 32.1 (kg/m(2)) for body mass index (BMI), 1.01 for waist-to-hip ratio (WHR), 158.7 mmHg and 103.8 mmHg for systolic (SBP) and diastolic blood pressure (DBP), 2.8 mmol/l for triglycerides, 6.2 mmol/l for blood glucose and 22.4 mU/l for serum insulin. There was a statistically significant difference in the mean values of BMI, WHR, SBP, DBP, HDL, triglycerides and blood glucose between the cluster representing the insulin resistance syndrome and the normal cluster.

CONCLUSIONS

This study shows that the multidimensional structures of insulin resistance syndrome can be visualized and identified at qualitative and quantitative level using the SOM algorithm.

Clustering of procoagulation, inflammation, and fibrinolysis variables with metabolic factors in insulin resistance syndrome

The known metabolic cardiovascular disease risk factors associated with insulin resistance syndrome (IRS) do not adequately explain the excess cardiovascular disease risk attributed to this syndrome, and abnormalities in hemostatic variables may contribute to this excess risk. Using data from 322 nondiabetic elderly men and women (aged 65-100 years) participating in the Cardiovascular Health Study during 1989-1990, the authors performed factor analysis on 10 metabolic risk factors associated with IRS and 11 procoagulation, inflammation, and fibrinolysis variables to examine the clustering of the metabolic and hemostatic risk markers. Factor analysis of the metabolic variables confirmed four uncorrelated factors: body mass, insulin/glucose, lipids, and blood pressure. Adding the hemostatic variables yielded three new factors interpreted as inflammation, vitamin K-dependent proteins, and procoagulant activity. Plasminogen activator inhibitor-1 clustered with the body mass factor, supporting the hypothesis that obesity is related to impaired fibrinolysis. Fibrinogen clustered with the inflammation summary factor rather than procoagulant activity, supporting the position that fibrinogen principally reflects underlying inflammation rather than procoagulant potential. The authors conclude that should hemostatic variables be shown to contribute to IRS-related cardiovascular disease, apart from plasminogen activator inhibitor-1, they may do so independently of the established metabolic abnormalities.

Occlusive vascular diseases in oral contraceptive users. Epidemiology, pathology and mechanisms

Despite being an unprecedented departure from normal physiology, the combined oral contraceptive is not only highly effective, but it also has a remarkably good safety record. Concerns over safety persist, though, particularly with regard to venous thromboembolism (VTE), stroke and myocardial infarction (MI). Epidemiological studies consistently show an increase in risk of VTE, but the results are more contentious with regard to arterial diseases. Despite 40 years of research, the mechanisms behind these adverse effects are not understood. In this review, we integrate information from published studies of the epidemiology and pathology of the occlusive vascular diseases and their risk factors to identify likely explanations for pathogenesis in oral contraceptive users. Oral contraceptives induce both prothrombotic and fibrinolytic changes in haemostatic factors and an imbalance in haemostasis is likely to be important in oral contraceptive-induced VTE. The complexity of the changes involved and the difficulty of ascribing clinical significance has meant that uncertainty persists. A seriously under-researched area concerns vascular changes in oral contraceptive users. Histologically, endothelial and intimal proliferation have been identified in women exposed to high plasma estrogen concentrations and these lesions are associated with thrombotic occlusion. Other structural changes may result in increased vascular permeability, loss of vascular tone and venous stasis. With regard to arterial disease risk, epidemiological information relating to dose effects and joint effects with other risk factors, and studies of pathology and changes in risk factors, suggests that oral contraceptive use per se does not cause arterial disease. It can, nevertheless, synergise very powerfully with subclinical endothelial damage to promote arterial occlusion. Accordingly, the prothrombotic effects of the oral contraceptive estrogen intervene in a cycle of endothelial damage and repair which would otherwise remain clinically silent or would ultimately progress - in, for example, the presence of cigarette smoking or hypertension - to atherosclerosis. Future work in this area should focus on modification of the effects of established risk factors by oral contraceptive use rather than modification of the supposed risk of oral contraceptive use by established risk factors. Attempts to understand vascular occlusion in oral contraceptive users in terms of the general features of VTE or with reference to atherosclerosis may be limiting, and future work needs to acknowledge that such occlusions may have unique features. Unequivocal identification of the mechanisms involved would contribute considerably to the alleviation of fears over vascular disease and to the development of even safer formulations.