Smoking and insulin sensitivity in type I diabetic patients

Smoking increases counterregulatory hormone secretion and reduces capillary flow, both of which could reduce insulin mediated glucose disposal. To evaluate whether smoking has any effect on body sensitivity to insulin, we measured insulin-mediated glucose disposal (1 mU euglycemic insulin clamp) during acute smoking in seven male type I diabetic patients. In addition, we performed a cross-sectional study to compare insulin sensitivity in 12 habitually smoking and 22 nonsmoking diabetic patients matched for age, relative body weight, sex, diabetes duration, HbA1, C-peptide, and insulin dose. In the acute study, baseline counterregulatory hormone levels were comparable in the smoking and control experiment. During smoking (9 to 12 cigarettes), carboxyhemoglobin level rose by 57% (P less than 0.01). Circulating adrenaline, cortisol, growth hormone, and glucagon levels were 40% to 100% higher during smoking than during the control clamp study (P less than 0.05-0.01). During acute smoking the rate of insulin-mediated glucose uptake (7.3 +/- 1.0 mg/kg/min) was not significantly different from that without cigarettes (6.8 +/- 0.7 mg/kg/min). In the cross-sectional study, the rate of glucose uptake was comparable in habitually smoking (5.0 +/- 0.5 mg/kg/min) and nonsmoking patients (4.8 +/- 0.3 mg/kg/min). Thus, inspite of a significant rise in counterregulatory hormones, neither acute nor habitual smoking causes substantial changes in insulin sensitivity in type I diabetics.