News & Research

Tuomilehto J, Hu G, Bidel S, et al.: Coffee consumption and risk of type 2 diabetes mellitus among middle-aged Finnish men and women. JAMA 291:1213-1219, 2004.

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

Coffee is the most popular beverage in the world. Many researchers have tried to find out if drinking coffee is healthy or unhealthy. Some studies say that drinking coffee may lower the risk of type 2 diabetes. People in Finland drink more coffee per person than people anywhere else in the world.

Who was studied?

Researchers studied a total of 14,629 Finnish people -- 6,974 men and 7,655 women. Their ages ranged from 25 to 64 years. None of them had heart disease, a stroke, or diabetes. They were studied for an average of 12 years.

How was the study done?

People in the study were picked at random. In questionnaires sent to their homes, they were asked how many cups of coffee they drank each day. They also were asked if they drank filtered coffee or coffee boiled in a pot.

Researchers put them in one of the following categories: 1 to 2 cups, 3 to 4 cups, 5 to 6 cups, 7 to 9 cups, and 10 or more cups each day. The people in the study also came to a study site, where nurses measured their height, weight, and blood pressure.

What did the researchers find?

By the end of the study, 381 people were found to have type 2 diabetes. However, the more coffee people drank, the less likely they were to have diabetes. This was true for both men and women. People who drank at least 10 cups a day had the lowest risk of diabetes. Light coffee drinkers had the same risk as non-coffee drinkers.

Men who drank pot-boiled coffee had 2.9 times the risk of diabetes than men who drank filtered coffee.

What were the limitations of the study?

None of the participants had a glucose tolerance test (one of the tests to tell if you have diabetes), so some cases of diabetes could have been missed. People in the study kept track of how much coffee they drank. These are called self-reported results. They are not always correct because people may lie or make mistakes.

What are the implications of the study?

We don't know why drinking more coffee is associated with a lower risk of type 2 diabetes. Researchers have several ideas, but the question needs more study.