Smoking cessation improves insulin sensitivity in healthy middle-aged men.

Cigarette smokers have recently been shown to exhibit insulin resistance, dyslipidaemia and markers of the insulin resistance syndrome (IRS). The aim of this study was to examine the effects of smoking cessation on insulin sensitivity and IRS. Forty male, non-obese healthy smokers participated in this open parallel study with 8 weeks of follow-up. Seventeen subjects were able to stop smoking, while 23 subjects continued to smoke and served as a controls group. Anthropometric and metabolic data were measured. Degree of insulin sensitivity was determined with the euglycaemic hyperinsulinaemic clamp technique. Smoking cessation increased insulin sensitivity and improved the lipoprotein profile in spite of a modest increase in body weight. Initial smoking habits correlated positively with the increase in BMI as well as the improvements in the metabolic variables after smoking cessation. These data support the view that smoking causes insulin resistance and IRS, and also demonstrate that the beneficial metabolic effects of smoking cessation override the effects of an accompanying modest increase in body weight.