In a new study, researchers found that coffee can help reduce the risk of developing type 2 diabetes — but only filtered coffee, rather than boiled coffee.
They found that the choice of preparation method influences the health effects of coffee.
The research was conducted by a team from Chalmers University of Technology and Umeå University, both in Sweden.
Filtered coffee is the most common method of preparation in many places, including the US and Scandinavia.
Boiled coffee in this case refers to an alternative method of coffee preparation sometimes used in Sweden and some 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.
Many previous studies have shown a connection between high coffee intake and a reduced risk of developing type 2 diabetes.
This new study offers new insight into this connection, using a novel method to help differentiate between the effects of filtered coffee and boiled coffee.
In the study, the team found specific molecules — ‘biomarkers’ — in the blood of those taking part in the study, which indicate the intake of different sorts of coffee.
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% lower risk of developing type 2 diabetes than people who drank less than one cup of filtered coffee a day.
Consumption of boiled coffee had no effect on diabetes risk in the study.
According to the team, 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.
The question is whether diterpenes also negatively influence sugar metabolism and are therefore the cause of why boiled coffee does not help lower the risk of diabetes, in the way that filter coffee does.
The researchers still cannot say the exact nature of the link.
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 the now popular coffee-pods, is also brewed without filters, the team believes the health effects could therefore be similar to boiled coffee, in terms of the risk of type 2 diabetes.
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 UK, would be more similar to filtered or boiled coffee in this respect.
But the researchers are careful to note that no conclusions can be drawn yet regarding these other preparation methods.
They also stress 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.
One author of the study is Rikard Landberg, Professor in Food Science at Chalmers.
The study is published in the Journal of Internal Medicine.
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