A recent genetic analysis has identified a biological pathway that may explain why filter coffee, in particular, may be associated with lower blood sugar levels.
The study — first published last December but corrected May 7 in npj Science of Food — used a method called Mendelian randomization to assess whether six different coffee consumption patterns had any causal relationship with HbA1c, the standard blood marker used to track average blood glucose.
The patterns assessed were filtered coffee, instant coffee with milk, filtered coffee with milk, coffee with added sugar, coffee with artificial sweeteners and decaffeinated coffee.
In the Mendelian randomization analysis, filtered coffee was significantly associated with lower HbA1c. None of the other five coffee-consumption patterns showed a statistically significant association.
Coming from a research team at the School of Nursing at Peking University in Beijing, China, the study drew from two large datasets: the UK Biobank, which holds data on more than 500,000 participants; and the MiBioGen consortium, which profiles gut bacteria across roughly 18,000 people.
The Gut Bacteria Connection
The researchers tested four gut bacteria known to produce propionic acid — a short-chain fatty acid with established links to insulin sensitivity and blood glucose regulation. All four — Veillonella, Akkermansia, Parabacteroides and Bifidobacterium — showed inverse associations with HbA1c levels. But only one, Veillonella, was significantly associated with filtered coffee consumption.
The authors noted that filtered coffee may retain relatively high levels of chlorogenic acid and other polyphenols while removing more coffee lipids. Those compositional differences may help explain why filtered coffee stood apart from decaf, sweetened coffee and coffee with milk or sweeteners, according to the authors.
Filters and the Gut
The new study touches upon two growing areas of interest in coffee-and-health research.
On the filtered coffee front, researchers at Chalmers University of Technology and Umeå University previously found that drinking two to three daily cups of filtered coffee was associated with a 60% lower type 2 diabetes risk.
A separate Swedish study found that coffee from many workplace brewing machines contained higher levels of cholesterol-elevating diterpenes than paper-filtered coffee, underscoring the health relevance of brewing and filtration methods.
On the microbiome front, one recent study identified Lawsonibacter asaccharolyticus as a coffee-linked gut bacterium whose presence and abundance were strongly associated with coffee consumption. Another recent study found that coffee consumption may help prevent depression by supporting the “gut-brain axis.”
This new paper touches both focus areas, adding a connection piece to the complex coffee-and-health puzzle.
The study was funded by the National Key Research and Development Program of China and two National Natural Science Foundation of China grants. The authors declared no competing interests.
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