Smoking and Type 2 Diabetes in Men

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The summary below is from the full report titled "Cigarette Smoking and Risk for Impaired Fasting Glucose and Type 2 Diabetes in Middle-Aged Japanese Men." It is in the 1 August 2000 issue of Annals of Internal Medicine (volume 133, pages 183-191). The authors are N. Nakanishi, K. Nakamura, Y. Matsuo, K. Suzuki, and K. Tatara.

What is the problem and what is known about it so far?

Insulin is a hormone that regulates how the body uses carbohydrates, protein, and fat. In type 2 diabetes, the type that develops during adulthood, the body's tissues lose their sensitivity to insulin. To overcome this resistance, the body produce more insulin, leading to high levels of insulin in the bloodstream. When even these high levels of insulin fail to overcome the tissue's resistance to insulin, abnormally high levels of blood sugar (glucose) develop. Some studies have suggested that cigarette smoking interferes with the body's ability to handle sugar (impaired fasting glucose) and contributes to the development of type 2 diabetes, but this relation remains uncertain.

Why did the researchers do this particular study?

To examine the association of cigarette smoking with the development of impaired fasting glucose and type 2 diabetes.

Who was studied?

The study included 1266 Japanese male office workers 35 to 59 years of age. The men did not have impaired fasting glucose or type 2 diabetes and were not taking medication for high blood pressure when they entered the study.

How was the study done?

The researchers measured the men's blood sugar levels yearly during regular health examinations form May 1994 to May 1999; this allowed them to determine who developed impaired fasting glucose or type 2 diabetes. They also collected information about the general characteristics and health histories of the men, including smoking histories and whether they took any medicine to treat diabetes.

What did the researchers find?

Eighty-seven of the men developed impaired fasting glucose and 54 developed type 2 diabetes during the study. After adjustment for other risk factors for diabetes (for example, overall obesity and family history of the disease), men who smoked more than 31 cigarettes per day were four times more likely than men who had never smoked to develop diabetes. Smoking also increased the risk for impaired fasting glucose.

What were the limitations of the study?

This study was done in Japan and included only middle-aged men; we therefore do not know if similar findings would occur in women, in men in other ethnic groups, or in people of different age groups. This study also does not tell us whether a person's chance of developing diabetes would decrease if he or she quit smoking.

What are the implications of the study?

Cigarette smoking appears to be a substantial risk factor for the development of diabetes.