Positive Health Online

Abstract

HIRAI and colleagues, Department of Cardiovascular Medicine, Kumamoto University School of Medicine, Kumamoto 860-8556, Japan. examined the effects of vitamin C on insulin sensitivity and endothelial function in smokers and non-smokers with impaired glucose tolerance (IGT) .

Background

Cigarette smoking impairs endothelial function and increases the risk of atherosclerosis and heart disease. Insulin resistance is associated with major risk factors for atherosclerosis.

Methodology

Effects of vitamin C infusion on endothelial function and insulin sensitivity were investigated in 16 current smokers and 15 non-smokers with IGT and in 17 non-smokers with normal glucose tolerance (controls). Insulin sensitivity was assessed by measuring steady-state plasma glucose (SSPG). Endothelial function was assessed by measuring flow-mediated dilation (FMD) of the brachial artery.

Results

Both smokers and non-smokers with IGT had abnormal SSPG and FMD compared with controls. In smokers (with IGT), vitamin C decreased SSPG with decreasing plasma thiobarbituric acid-reactive substances (TBARS) and improved FMD . Vitamin C also improved SSPG and FMD in non-smokers with IGT . Vitamin C did not alter SSPG, FMD or TBARS in controls.

Conclusion

Insulin sensitivity and endothelial function were impaired in smokers and non-smokers with IGT. Vitamin C infusion improved both these parameters . The findings indicate that, in smokers and non-smokers with IGT, increased reactive oxygen species play an important role in the pathogenesis of both insulin resistance and endothelial dysfunction.

References

Hirai N et al. Insulin resistance and endothelial dysfunction in smokers: effects of vitamin C. American Journal of Physiology. Heart and Circulatory Physiology 279 (3): H1172-8. Sep 2000.