Cigarette smoking is a modifiable risk factor for impaired insulin secretion in Japanese men, show study findings.
In a study of 1199 men without diabetes, impaired insulin secretion, or insulin resistance at baseline, the risk for impaired insulin secretion was increased two-fold in current smokers compared with never smokers, report Akiko Morimoto (Osaka University, Japan) and colleagues.
However, ex-smokers were not at an increased risk for impaired insulin secretion, suggesting that cigarette smoking is a modifiable risk factor that could be targeted for the prevention of Type 2 diabetes.
For the study, Morimoto and colleagues determined the insulinogenic index and homeostatic model assessment of insulin resistance among the men (aged 30‑79 years) who underwent an oral glucose tolerance test (OGTT) at baseline and were followed up over a mean of 2.8 years.
As reported in the Journal of Diabetes Investigation, the team found that the incidence rates for impaired insulin secretion per 1000 person-years were 120 in never-smokers, 125 in ex-smokers, and 165 in current smokers.
The likelihood of current smokers having impaired insulin secretion was increased by a significant 1.95-fold compared with never smokers, while it was only increased 1.06-fold in ex-smokers, after adjustment for confounders including age, family history of diabetes, alcohol consumption, exercise, systolic blood pressure, triglyceride, γ-glutamyltransferase, waist circumference, leukocyte count, and changes in smoking status and waist circumference.
Incidence rates for insulin resistance per 1000 person-years were 18 in never-smokers, 22 in ex-smokers, and 38 in current smokers.
The hazard ratios for insulin resistance were 1.04 in ex-smokers and 1.93 in current smokers compared with never smokers, after adjustment for age, family history of diabetes, alcohol consumption, exercise, systolic blood pressure, triglycerides, and γ-glutamyltransferase. However, after further adjustment for leukocyte count, changes in smoking status, and changes in waist circumference, this increased risk was attenuated and was no longer significant.
"A greater amount of visceral adipose tissue is related to insulin resistance and diabetes," note Morimoto et al. "Smokers tend to have a larger waist circumference than nonsmokers. The impact of current smoking on insulin resistance, might be, in part, mediated by visceral adipose tissue, visceral adipose tissue gain and systemic inflammation."
The team also reports that the number of pack-years was positively associated with the risk for impaired insulin secretion in a dose-dependent manner, indicating the long-term effect of cigarette smoking for current smokers.
The team says the findings might also be important for other Asian populations which have low insulin secreting ability.
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