Filter Coffee Tied to Lower Diabetes Risk in Metabolomics Study

Marlene Busko

December 31, 2019

In a Swedish case-control study, drinking filtered coffee was associated with a lower 10-year risk of developing type 2 diabetes than abstaining from coffee completely, but the same was not true for drinking boiled coffee.

The researchers used liquid chromatography–mass spectrometry to identify metabolites in the serum of adults who drank filtered coffee rather than boiled coffee.

Adults who drank two to three cups of filtered coffee a day (the highest quartile of filtered coffee–metabolite score) had a 58% lower risk of developing type 2 diabetes within 10 years than those who drank fewer than one cup of filtered coffee a day (lowest quartile) after adjusting for multiple confounders (odds ratio, 0.42; 95% confidence interval, 0.23 – 0.75).

The protective effect of drinking this high amount on the risk of developing type 2 diabetes was not seen with boiled coffee.

With filtered coffee, finely ground coffee beans are placed in a filter, through which water then passes, either in a machine or manually. Boiled coffee is made with coarsely ground coffee beans that are then added directly to the water. This method includes Turkish and Greek coffee, or espresso-based drinks, which are most common in Southern Europe.

Sweden is among the countries with the highest filtered coffee intake worldwide, but in Sweden the consumption of boiled coffee is also high, especially in the large, rural areas of northern Sweden.

In the United States, filtered coffee is the most common variety. Instant coffee is predominant in the United Kingdom.

Does Filter Get Rid of Harmful Molecules?

The study findings therefore support "a protective role of habitual intake of filtered coffee on [type 2 diabetes] development," say Lin Shi, PhD, a postdoctoral researcher at Chalmers University of Technology in Gothenburg, Sweden, and colleagues in their study, published online December 9 in the Journal of Internal Medicine.

Senior author Rikard Landberg, PhD, professor of food and nutrition science at Chalmers University of Technology, further qualified this in an email to Medscape Medical News: "We found that the molecules previously associated with increased risk of cardiovascular disease (diterpenes) were highly present among boiled coffee consumers but not among filtered coffee consumers.

"We think that these molecules may have adverse effects on type 2 diabetes risk," he continued, "and studies have previously shown that these molecules get stuck in the filter paper."

Intake of instant coffee, espresso, cafetière (French press) coffee, and percolator coffee was not common among the Swedish population studied when the data were collected.

But given that espresso coffee ― or the now popular coffee-pod ― is also brewed without filter paper, Landberg believes the health effects could be similar to that of boiled coffee regarding the risk for type 2 diabetes. Thus, "it is likely that these [harmful metabolites] are still present, unless other means have been taken to remove them," he said. He cautioned that this would need to be confirmed in further studies.

And coffee made in a cafetière, or French press, is prepared in a way similar to that of boiled coffee, so drinking coffee made that way may also not reduce type 2 diabetes risk, he added. Again, he and his fellow researchers are careful to note that no firm conclusions can be drawn yet regarding these other preparation methods.

It is also unclear whether instant coffee, the most popular type in the United Kingdom, is similar to filtered or boiled coffee in this respect, he said.

Moreover, "one should also remember that the levels of the 'adverse' molecules are dependent on several factors, such as roasting, cultivation, etc," he added, "and it is difficult to generalize unless the different brews are analyzed."

In Sweden, a cup of coffee is defined as containing 1.5 dL, he explained, "so two to three cups a day corresponds to 300 to 450 mL of coffee." Other countries may differ in this respect.

Nevertheless, according to the researchers, "the present study demonstrates the potential of using metabolite biomarkers specific for coffee brews as a complement to traditional dietary assessment in investigating their role in [type 2 diabetes] development, especially in existing cohorts where consumption data of different coffee brews are lacking.

"Identified metabolites should be further investigated as candidate biomarkers of specific intakes of filtered and boiled coffee in future studies," they conclude.

Could Plasma Metabolites in Coffee Drinkers Predict Diabetes Risk?

Previous studies that have examined the association between coffee consumption and risk of developing type 2 diabetes utilized food frequency questionnaires and did not distinguish between different types of coffee preparation, the authors write.

In the current study, the investigators aimed to identify plasma metabolites associated with the two common types of coffee consumed in northern Sweden (filtered and boiled) and then see how coffee consumption was associated with risk for type 2 diabetes.

They identified 149 adults (86 men, 63 women) who enrolled in the prospective Västerbotten Intervention Programme (VIP) study from 1995 to 2005 and who developed type 2 diabetes during the next 10 years.

These participants were matched with 149 similar participants who did not develop diabetes.

The researchers identified 12 metabolites in plasma that predicted boiled coffee intake and 10 metabolites that predicted filtered coffee intake.

The strongest predictors of boiled coffee intake were the diterpenes.

However, this was an observational study, so it cannot show a causal effect, nor was it designed to investigate a potential biological mechanism, the authors stress.

Nevertheless, the research illustrates how "metabolomics is a fantastic tool, not just for capturing the intake of specific foods and drinks, but also for studying the effects that that intake has on people's metabolism," said Shi in a press release issued by the university.

"We can derive important information on the mechanisms behind how certain foods influence disease risk," she concluded.

The study was supported by grants from the Swedish University of Agricultural Sciences and the Swedish Research Council for Health, Working Life and Welfare. The authors have disclosed no relevant financial relationships.

J Inter Med. Published online December 9, 2018. Abstract

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