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Filtered coffee helps prevent type 2 diabetes

New research from the Chalmers University of Technology and Umeå University, both in Sweden, shows that the preparation methods can influence the health effects of coffee.

For instance, the studies found that coffee can help reduce the risk of developing type 2 diabetes, but only filtered coffee rather than boiled coffee.

Researchers says many previous studies have shown a connection between high coffee intake and a reduced risk of developing type 2 diabetes.

"We have identified specific molecules - 'biomarkers' - in the blood of those taking part in the study, which indicate the intake of different sorts of coffee. These biomarkers are then used for analysis when calculating type 2 diabetes risk,” says Rikard Landberg, Professor in Food Science at Chalmers, and Affiliated Professor at the Department of Public Health and Clinical Medicine at Umeå University.

“Our results now clearly show that filtered coffee has a positive effect in terms of reducing the risk of developing type 2 diabetes. But boiled coffee does not have this effect."

With the use of these biomarkers, the researchers were able to show that people who drank two to three cups of filtered coffee a day had a 60 per cent lower risk of developing type 2 diabetes than people who drank less than one cup of filtered coffee a day.

Filtered coffee is the most common method of preparation in many places, including the United States and Scandinavia. Boiled coffee in this study refers to an alternative method of coffee preparation sometimes used in Sweden and other countries, in which coarse ground coffee is simply added directly to boiling water and left to brew for a few minutes. All the data used in the research came from a group of Swedish subjects and was collected in the early 1990s.

According to Landberg, many people wrongly believe that coffee has only negative effects on health. This could be because previous studies have shown that boiled coffee increases the risk of heart and vascular diseases, due to the presence of diterpenes, a type of molecule found in boiled coffee.

"But it has been shown that when you filter coffee, the diterpenes are captured in the filter. As a result, you get the health benefits of the many other molecules present, such as different phenolic substances. In moderate amounts, caffeine also has positive health effects," he says.

Many other types of coffee preparation were not specifically investigated in the study, such as instant, espresso, cafetière, and percolator coffee. These types of coffee were not common among the Swedish study population when the data was collected.

But given that espresso coffee, from classic espresso machines or coffee pods, is also brewed without filters, Landberg believes the health effects could therefore be similar to boiled coffee.

Coffee made in a cafetière, or French press, is prepared in a similar way to boiled coffee, so it may also not have the positive effect of reducing type 2 diabetes risk. It is unclear whether instant coffee, the most popular type in the United Kingdom, would be more similar to filtered or boiled coffee in this respect.

Researchers are careful to note that no conclusions can be drawn yet regarding these other preparation methods. Landberg also stresses that the health impacts of coffee do not depend solely on if it is filtered or not. They also vary with how the coffee beans, and the drink in general, are managed.

The study was a case-control study nested in a prospective cohort in the Västerbotten region of northern Sweden between 1991 and 2005. Participants answered questionnaires about eating habits and lifestyle. They also left blood samples which were stored frozen. From those who took part, a total of 421 people were identified who, after around seven years, had developed type 2 diabetes. They were compared with 421 healthy control subjects. The original blood samples were then analysed. In addition, blood samples that had been provided ten years after the first blood samples were analysed for 149 of the case-control pairs.

The paper can be read here.

Image: Yen Strandqvist, Chalmers University of Technology

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