Improvement of endothelial function and insulin sensitivity with vitamin C in patients with coronary spastic angina: possible role of reactive oxygen species

OBJECTIVES

This study was designed to examine the effect of antioxidant supplementation on the endothelial function and insulin sensitivity in patients with coronary spastic angina (CSA).

BACKGROUND

Insulin resistance may play a key role in coronary heart disease, and there is a possible link between acetylcholine-induced coronary vasoconstriction and hyperinsulinemia in patients with CSA. Endothelial dysfunction is present in the systemic arteries in CSA patients, and reactive oxygen species may cause inactivation of nitric oxide in these patients.

METHODS

We measured flow-mediated dilation of the brachial artery using ultrasound technique in 22 patients with CSA and 20 control subjects. We also evaluated glucose tolerance using a 75-g oral glucose tolerance test and insulin sensitivity using steady-state plasma glucose (SSPG) methods in the same patients.

RESULTS

The incidence of impaired glucose tolerance was higher in the CSA group than in the control group. Vitamin C infusion augmented flow-mediated dilation and decreased SSPG levels in the CSA group (from 3.27 ± 0.77% to 7.00 ± 0.59% [p < 0.001 by analysis of variance (ANOVA)] and from 177.3 ± 13.3 to 143.1 ± 14.9 mg/dl [p = 0.047 by ANOVA], respectively) but not in the control group (from 6.47 ± 0.66% to 6.80 ± 0.60% and from 119.8 ± 11.7 mg/dl to 118.1 ± 11.3 mg/dl, respectively). The steady-state plasma insulin levels were not affected by vitamin C infusion in either group.

CONCLUSIONS

Vitamin C improves both endothelial function and insulin sensitivity in patients with CSA. Thus, reactive oxygen species and/or decreased nitric oxide bioactivity may play an important role in the genesis of both endothelial dysfunction and insulin resistance in patients with CSA.     

Ageing and associations of fasting plasma glucose and 2 h plasma glucose with HbA(1C) in apparently healthy population. "FIN-D2D" study

Objective

In this FIN-D2D cross-sectional survey the relationship of age with HbA_1c and fasting and 2 h glucose in the oral glucose tolerance test (OGTT) was explored in apparently randomly selected healthy population.

Patients and methods

The glycaemic parameters were measured in 1344 men and 1482 women (aged 45–74 years), and among them we excluded all subjects with known diabetes, hypertension or dyslipidaemia. The final analyses for HbA_1c and the ratios of fasting glucose/HbA_1c and 2 h glucose/HbA_1c included 649 men and 804 women.

Results

Mean age was 57 years and BMI 26.1 kg/m² for both genders. HbA_1c increased in both genders with age (p < 0.001). For a particular fasting glucose level HbA_1c level was higher in older age groups (p < 0.001 for linearity). By contrast, a particular 2 h plasma glucose value in OGTT implied significantly lower HbA_1c in the elderly (p < 0.001 for linearity).

Conclusion

In apparently healthy population, screened with OGTT, in older individuals compared with younger ones a particular HbA_1c value implies slightly lower fasting glucose, but relatively higher 2 h glucose. These results need to be verified in different populations. The effects of age on relation between HbA_1c and plasma glucose should be taken into account in classifying people into different dysglycaemia categories.