Smoking is associated with insulin resistance and cardiovascular autonomic dysfunction in type 2 diabetic patients

Background  Smoking and cardiovascular autonomic dysfunction are associated with high mortality in type 2 diabetic patients. This study tested the hypothesis that smoking is associated with insulin resistance/hyperinsulinaemia and cardiovascular autonomic dysfunction in type 2 diabetic patients who are not treated with insulin. Materials and methods  The study patients were 22 current smokers with type 2 diabetes mellitus (age: 57 ± 5 years, mean ± SD) and 30 age-matched never-smoked patients with type 2 diabetes mellitus (control group, 57 ± 8 years). The quality of blood glucose was assessed by fasting plasma glucose (FPG), fasting immunoreactive insulin (F-IRI), homeostasis model assessment (HOMA) index and haemoglobin A1c (HbA1c). The severity of smoking status was expressed by the Brinkman index, which is calculated as number of cigarettes per day multiplied by years of smoking. Cardiovascular autonomic function was assessed by baroreflex sensitivity (BRS), heart-rate variability, plasma norepinephrine concentration and cardiac 123I-metaiodobenzylguanidine (MIBG) scintigraphic findings. Results  Baroreflex sensitivity was lower in the current smokers group than in the never-smoked group (P < 0·05). Early and delayed 123I-MIBG myocardial uptake values were lower (P < 0·05, and P < 0·01, respectively) and the percentage washout-rate of 123I-MIBG was higher (P < 0·0001) in the current smokers group than in the never-smoked group. Fasting immunoreactive insulin (F-IRI) concentration (P < 0·0001) and the homeostasis model assessment (HOMA) index (P < 0·0001) were higher in the current smokers group than the never-smoked group. Multiple logistic regression analysis revealed that smoking was independently predicted by F-IRI and the percentage washout-rate of 123I-MIBG. Conclusions  The results of the study suggested that smoking was associated with cardiovascular autonomic dysfunction and hyperinsulinaemia and that F-IRI and the percentage washout-rate of 123I-MIBG were independent predictors of smoking in these Japanese patients with type 2 diabetes mellitus.