Smoking is independently associated with high plasma insulin levels in nondiabetic men

OBJECTIVE - Studies using the euglycemic clamp technique or the insulin suppression test in relatively small numbers of subjects have suggested that smoking may cause insulin resistance. Our aim was to study the association between smoking status and fasting plasma insulin in a large nondiabetic male population. RESEARCH DESIGN AND METHODS - A total of 616 nondiabetic men aged 45-64 years were taken from a population register. Fasting plasma insulin and blood pressure were measured, and smoking history and medication were evaluated by interview. RESULTS - Age- and BMI-adjusted insulin levels were significantly higher in smokers and ex-smokers than in nonsmokers (92.4, 86.4, and 78.6 pmol/l, respectively; P = 0.009). In every BMI-tertile, smokers and ex-smokers had higher plasma insulin than nonsmokers. After adjustment for factors potentially affecting insulin sensitivity (hypertension, systolic or diastolic blood pressure, use of beta-blockers and/or diuretics, use of vasodilating antihypertensive drugs, physical exercise, alcohol use, parental history of NIDDM, coronary heart disease, and previous myocardial infarction), insulin concentrations were still highest in smokers (91.2 pmol/l), intermediate in ex-smokers (86.8 pmol/l), and lowest in nonsmokers (78.9 pmol/l, P = 0.008 between groups). CONCLUSIONS - Our results show that chronic smoking is associated with high age- and BMI-adjusted plasma insulin levels, independent of other factors known to influence insulin sensitivity. The effect of smoking may be partially reversible after quitting.