News & Research

The relationship between green tea and total caffeine intake and risk for self-reported type 2 diabetes among Japanese adults, by H. Iso and colleagues. Ann Intern Med, 144:554-562, 2006.

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

Research suggests that people who drink coffee are less likely to get type 2 diabetes. It isn't known whether the caffeine or some other ingredient in coffee is responsible for its protective effects.

Why did the researchers do this particular study?

The researchers wanted to see whether there is a link between diabetes and drinking coffee and green, black, and oolong tea.

Who was studied?

The study included 17,413 men and women in 25 communities across Japan. They were between 40 and 65 years old, and about half of them had diabetes.

How was the study done?

Participants completed a detailed questionnaire about their health, lifestyle habits, and how much coffee and tea they drank. The questionnaire was repeated at the end of the 5-year follow-up period.

What did the researchers find?

When other factors were accounted for, researchers found that the more green tea and coffee participants drank, the less likely they were to get diabetes. People who drank six cups or more of green tea or three or more cups of coffee each day were about one-third less likely to get diabetes. The link was stronger in women than in men. No pattern was seen with black or oolong tea.

What were the limitations of the study?

Information about tea consumption was based on what participants recalled and reported, which may not be accurate. Similarly, researchers did not do a physical exam or blood tests on participants, but relied on people to provide information about health issues that may not be complete or accurate.

What are the implications of the study?

Green tea and coffee may offer some protection against type 2 diabetes.

FOR MORE INFORMATION

Essential Water: Make Sure You Get Enough

Drinking More Coffee May Lower Risk of Type 2 Diabetes

Caffeine, Exercise, and Glucose