Cigarette smoking, environmental tobacco smoke exposure and insulin sensitivity: the Insulin Resistance Atherosclerosis Study

Minimal model-based insulin sensitivity has greater heritability and a different genetic basis than homeostasis model assessment or fasting insulin

Insulin resistance is an important risk factor for development of type 2 diabetes as well as other chronic conditions, including hypertension, cardiovascular disease, and colon cancer. To find genes for insulin resistance it is necessary to assess insulin action in large populations. We have previously measured insulin action in a large cohort of subjects (Insulin Resistance and Atherosclerosis Study [IRAS] Family Study) using the minimal model approach. In this study, we compare sensitivity from the minimal model (insulin sensitivity index [S(I)]) with the measure of insulin resistance emanating from the homeostasis model assessment (HOMA) approach. The former measure emerges from the glycemic response to endogenous and exogenous insulin; the latter is based solely on fasting measures of glucose and insulin. A total of 112 pedigrees were represented, including 1,362 individuals with full phenotypic assessment. Heritability of S(I) was significantly greater than that for HOMA (0.310 vs. 0.163) and for fasting insulin (0.171), adjusted for age, sex, ethnicity, and BMI. In addition, correlation between S(I) and either HOMA or fasting insulin was only approximately 50% accounted for by genetic factors, with the remainder accounted for by environment. Thus S(I), a direct measure of insulin sensitivity, is determined more by genetic factors rather than measures such as HOMA, which reflect fasting insulin.

The metabolic syndrome in smokers. The D.E.S.I.R. study

OBJECTIVES

To test the hypothesis that smokers have a higher frequency of the metabolic syndrome, and a syndrome with different characteristics than non-smokers.

MATERIAL AND METHODS

The 2,569 men and 2,637 women included in the D.E.S.I.R. study, aged 30-64 years, volunteers from ten French Social Security Health Examination Centres, were studied. The World Health Organization definition of the metabolic syndrome was adapted for this analysis, and insulin resistance was defined by a concentration above the 75(th) centile of the sex-specific distribution of fasting insulin.

RESULTS

28.1% of men and 15.1% of women were current smokers. The metabolic syndrome was twice as frequent in men than in women (22.8% vs 11.0%). Smokers and never-smokers were compared in age stratified samples. In men, the frequencies of hyperglycaemia or hypoglycaemic treatment, dyslipidaemia, microalbuminuria, and central obesity were significantly higher in smokers and 22.5% of smokers and 15.3% of non-smokers had this syndrome (p=0.001). In women, only dyslipidaemia was more frequent in smokers; in contrast smokers had lower insulin concentrations and hence a lower frequency of hyperinsulinemia. The frequency of the syndrome did not differ between women who smoked and those who did not (6.3% vs 6.0%).

CONCLUSIONS

In men, the metabolic syndrome was more frequent in smokers than in non-smokers; in contrast, there was no difference for women. For both sexes, syndrome abnormalities tended to be more frequent in smokers than in non-smokers.

Lung function, insulin resistance and incidence of cardiovascular disease: a longitudinal cohort study

OBJECTIVES

To explore whether a reduced lung function is a risk factor for developing diabetes and insulin resistance (IR), and whether such relationship contributes to the largely unexplained association between lung function and incidence of cardiovascular disease (CVD).

DESIGN

Forced vital capacity (FVC) was assessed at baseline. Incidence of diabetes and IR [according to the homeostasis model assessment (HOMA) model] was assessed in a follow-up examination after 13.9 +/- 2.6 and 9.4 +/- 3.6 years for men and women, respectively. After the follow-up examination, incidence of CVD (stroke, myocardial infarction or cardiovascular death) was monitored over 7 years.

SETTING

Populations-based cohort study.

SUBJECTS

Initially nondiabetic men (n = 1436, mean age 44.6 years) and women (n = 896, mean age 49.8 years).

RESULTS

Prevalence of IR at the follow-up examination was 34, 26, 21 and 21%, respectively, for men in the first (lowest), second, third and fourth quartile of baseline FVC (P for trend <0.0001). The corresponding values for women were 30, 29, 25 and 17%, respectively (P for trend <0.001). Adjusted for potential confounders, the odds ratio (OR) for IR (per 10% increase in FVC) was 0.91 (CI: 0.84-0.99) for men and 0.89 (CI: 0.80-0.98) for women. FVC was similarly significantly associated with the incidence of diabetes (OR = 0.90, CI: 0.81-1.00), adjusted for sex and other confounders. The incidence of CVD after the follow-up examination was significantly increased only amongst subjects with low FVC who had developed IR (RR = 1.7, CI: 1.02-2.7).

CONCLUSION

Subjects with a moderately reduced FVC have an increased risk of developing IR and diabetes. This relationship seems to contribute to the largely unexplained association between reduced lung function and incidence of CVD.

Insulin resistance and compensatory hyperinsulinemia: the key player between cigarette smoking and cardiovascular disease?

Hyperinsulinemia, dyslipidemia, and endothelial dysfunction are characteristic findings in insulin-resistant individuals, and all of these abnormalities have been identified as increasing cardiovascular disease (CVD) risk. Smokers tend to be relatively insulin resistant, hyperinsulinemic, and dyslipidemic, with evidence of endothelial dysfunction, as compared with nonsmokers, and recent epidemiologic data have suggested that CVD in smokers is primarily seen in those individuals who also have the characteristic findings of insulin resistance. Based on these observations, it is argued that insulin resistance and its consequences represent a major mechanistic link between cigarette smoking and CVD. It is also postulated that the enhanced CVD risk in smokers, resulting from hyperinsulinemia, abnormalities of lipoprotein metabolism, and endothelial dysfunction, will primarily be present in those smokers who are insulin resistant. As a corollary, it is suggested that CVD risk in individuals who cannot, or will not, stop smoking can be reduced by therapeutic efforts aimed at attenuating the adverse effects of insulin resistance and its consequences.

Alcohol consumption in the severely obese: relationship with the metabolic syndrome

OBJECTIVE

The aim of this study was to examine the association between the clinical and biochemical features of the metabolic syndrome and quantity and type of alcohol intake in the severely obese.

RESEARCH METHODS AND PROCEDURES

A cross-sectional study was performed in 486 consecutive severely obese subjects. Data on alcohol consumption was collected by serial clinical interviews and a questionnaire. The relationship between alcohol intake and the clinical and serum chemistry features of the metabolic syndrome was analyzed by multiple statistical techniques. Laboratory measures included lipid profile, fasting blood glucose, hemoglobin A1c, and fasting serum insulin. An indirect index of insulin resistance was calculated using the log-transformed fasting insulin and glucose product.

RESULTS

There were 486 subjects, 84% women, with a mean age of 40.6 +/- 10 years (range, 16 to 71 years) and a body mass index of 45.3 +/- 7 kg/m(2) (range, 34 to 77 kg/m(2)). Alcohol consumers (N = 276) showed a marked reduction in the adjusted odds ratio of type 2 diabetes (odds ratio = 0.29; 95% confidence interval, 0.16 to 0.55) compared with rare or nonconsumers (N = 210). There was a U-shaped relationship between the amount and frequency of alcohol consumption and fasting triglyceride, fasting glucose, hemoglobin A1c, and index of insulin resistance measurements. Consumers of < 100 g/wk had more favorable measures. The effect was attenuated when diabetics were excluded from the analysis. Timing of alcohol consumption did not influence outcome measures.

DISCUSSION

Light-to-moderate alcohol consumption is associated with a lower prevalence of type 2 diabetes, reduced insulin resistance, and more favorable vascular risk profile in the severely obese. We would propose that light to moderate alcohol consumption should not be discouraged in the severely obese.