How coffee helps lower type 2 diabetes risk: New clues on mechanism

The study’s authors analyzed a large data set from participants in two population-based studies: the United Kingdom’s UK Biobank and the Netherlands’ Rotterdam Study.

The UK Biobank cohort included 502,536 individuals from England, Scotland, and Wales who began participating in the study between April 2006 and December 2010. They were 37 to 73 years old. In 2017, follow-up data on these individuals became available.

The Rotterdam Study, which began in 1990, is ongoing, ultimately involving 14,929 individuals. Follow-up data was released in 2015.

In the study, researchers observed changes in the levels of inflammation-related biomarkers related to type 2 diabetes.

Dr. Angélica Amato, associate professor in the Faculty of Health Sciences at the University of Brasília, not involved in the current study, noted that its “main strength […] is the large number of individuals included in the cohorts, the long follow-up time, and the comprehensive assessment of inflammatory markers.”

Lead author Dr. Carolina Ochoa-Rosales, a postdoctoral scientist in nutrition and genetic epidemiology at Erasmus University Medical Centre Rotterdam, in the Netherlands, told Medical News Today that “[t]ype 2 diabetes is partly considered an inflammatory disease, and it is accepted that higher concentrations of pro-inflammatory markers in plasma constitute a risk factor for type 2 diabetes.”

The study found that drinking coffee boosts levels of the anti-inflammatory adipokine hormone adiponectin, as well as cytokine interleukin-13, or IL-13. At the same time, coffee consumption decreases levels of C-reactive protein (CRP) and leptin, which promote inflammation.

“CRP is an inflammation marker that reflects intracellular damage,” explained endocrinologist Dr. Ana Maria Kausel, who was not involved in the study.

The study authors determined that coffee affected CRP most strongly in people who drank more than 4 cups of coffee a day.

The Food and Drug Administration (FDA) advises that adults drink no more than 400 milliliters (ml) of caffeine a day or 4–5 cups of coffee.

Dr. Amato cautioned that a longitudinal study such as this one could not establish causality with certainty. However, she remarked, “it is most likely that the link between coffee consumption and reduced type 2 diabetes risk is due to decreased insulin resistance, one of the physiopathological mechanisms underlying the development of type 2 diabetes.”

In people with type 2 diabetes, insulin produced by the pancreas cannot control blood sugar levels. Such insulin resistance allows these levels to rise dangerously out of control.

“Insulin resistance is largely determined by subclinical inflammation, which is apparently improved by coffee consumption,” said Dr. Amato.

“Adipokine […] secreted by adipocytes, makes patients more sensitive to insulin [in addition to having] anti-inflammatory effects,” Dr. Kausel added.

For those concerned with avoiding type 2 diabetes, Dr. Ochoa-Rosales suggested taking a stand against inflammation by choosing a diet that is rich in polyphenols derived from fruits and vegetables.

The researchers also found that coffee’s beneficial effect was diminished among individuals who currently smoke.

Initially, the researchers considered smoking a confounding factor in their analysis, said Dr. Ochoa-Rosales, “since there is a correlation between smoking and higher coffee consumption — heavy coffee drinkers are often smokers.”

Nonetheless, when they compared the effect of coffee consumption on diabetes risk among smokers, non-smokers, and never-smokers, they found that coffee’s beneficial association with lower C-reactive protein and type 2 diabetes risk was an effect only present among former- and never-smokers.

Dr. Kausel noted that while the relationship between inflammation markers and cardiovascular disease has been studied, the new research brings a “different perspective.”

Although simply drinking more coffee is unlikely to prevent type 2 diabetes, “[a]nything that lowers these inflammation markers can be acquired as a daily routine, and since most people consume coffee, it’s a good thing to know,” she added.

As a result of a large body of evidence implicating systemic inflammation in developing type 2 diabetes, said Dr. Ochoa-Rosales, there is already heightened interest in treatments targeting inflammatory biomarkers.

Acknowledging this, Dr. Amato said that the biomarkers measured in the study might also be “promising targets” for therapeutically addressing type 2 diabetes:

“Another exciting possibility is exploring how exactly the bioactive substances in coffee act to unravel novel pathways and targets that could be addressed to treat or prevent the disease.”

Dr. Kausel cautioned that whatever new drug targets may be revealed in studies such as this one, “if people don’t start thinking about healthier habits, it will be impossible to prevent the disease.”

“The main factor in diabetes prevention is a healthy diet,” emphasized Dr. Kausel.