Increased level of hemoglobin A1c, but not impaired insulin sensitivity, found in hypertensive and normotensive smokers.

Smoking is associated with an abnormal plasma lipoprotein pattern. Recently, both insulin resistance and normal insulin action have been reported in smokers. In a total of 191 hypertensive and normotensive subjects recruited from a health survey, serum lipoprotein lipids, glucose tolerance (by intravenous glucose tolerance test (IVGTT), insulin secretion, and insulin sensitivity (euglycemic insulin clamp) were compared in the 41 smokers and 150 nonsmokers. Subjects were examined in the morning during a fasting state and after abstinence from smoking for 10 to 12 hours. Smokers showed a higher level of hemoglobin A1c (HbA1c) as compared with nonsmokers, 4.9% versus 4.7% (P < .05). There were no significant differences in fasting glucose, insulin, or insulin-mediated glucose disposal. However, a number of indices of insulin sensitivity tended to show enhanced insulin action among smokers. Only lower glucose and insulin values during the late phase (40 to 90 minutes) of the IVGTT reached statistical significance. Compared with nonsmokers, smokers had an expected higher level of serum triglycerides (2.1 v 1.8 mmol/L, P < .05) and an increased low-density lipoprotein (LDL) to high-density lipoprotein (HDL) cholesterol ratio (4.5 v 3.9, P < .05). These differences between smokers and nonsmokers were similar in both hypertensives and normotensives. In conclusion, smokers examined in the abstinence phase showed no signs of impaired insulin action. Lipoprotein abnormalities and elevated HbA1c may be caused in part by the insulin resistance induced during acute smoking and therefore may be quantitatively related to the time exposed to smoking. The effect on insulin sensitivity appears to be reversible over 10 to 12 hours.