Coffee Drinkers at Lower Risk for Type 2 Diabetes

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The summary below is from the full report titled "Coffee Consumption and Risk for Type 2 Diabetes Mellitus." It is in the 6 January 2004 issue of Annals of Internal Medicine (volume 140, pages 1-8). The authors are E. Salazar-Martinez, W.C. Willett, A. Ascherio, J.E. Manson, M.F. Leitzmann, M.J. Stampfer, and F.B. Hu.

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

Type 2 diabetes mellitus is a common disease that interferes with the body's ability to store energy from food. The pancreas makes insulin, a substance that helps to store energy from food. In people with type 2 diabetes mellitus, the body makes plenty of insulin but cannot use it normally. The result is high blood sugar levels. Over time, high blood sugar levels can lead to blindness, kidney failure, nerve damage, and heart disease. Risk factors for type 2 diabetes mellitus include being overweight, lack of exercise, and family history of the disease. Because type 2 diabetes mellitus is common and has serious complications, it is important to understand factors associated with the disease. It is known that caffeine influences the way the body handles sugar. A recent study in the Netherlands showed that people who drank at least 7 cups of coffee a day were half as likely to develop type 2 diabetes mellitus as people who drank 2 cups or less a day. However, this study did not separate regular from decaffeinated coffee and did not ask the participants about other caffeine-containing drinks.

Why did the researchers do this particular study?

To examine the relationships between type 2 diabetes mellitus and drinking any type of coffee, regular coffee, decaffeinated coffee, and all caffeine-containing drinks.

Who was studied?

41,934 men who had participated in the Health Professionals Follow-up Study and 84,276 women who had participated in the Nurses' Health Study. Participants did not have diabetes, cancer, and heart disease at the start of those large studies of various health issues.

How was the study done?

The men and women in the Health Professionals Follow-up Study and the Nurses' Health Study completed questionnaires every 2 to 4 years that included questions about how frequently they drank coffee and other beverages. The surveys also collected information on health conditions, including type 2 diabetes mellitus. The researchers then compared the frequency with which type 2 diabetes mellitus developed in several groups of people with different intakes of coffee and other caffeine-containing drinks.

What did the researchers find?

While accounting for other diabetes risk factors, such as body size, the researchers found that people who drank more coffee were less likely to develop type 2 diabetes mellitus. This relationship was stronger in women than in men. The researchers did not find a relationship between decaffeinated coffee intake and type 2 diabetes mellitus.

What were the limitations of the study?

The design of this study does not permit the researchers to be certain that coffee decreases incidence of type 2 diabetes mellitus. It might be something else about coffee drinkers that protects them from diabetes.

What are the implications of the study?

This study suggests that further research should examine the influence of caffeine on sugar metabolism.