Type 2 diabetes, which affects around 1 in 10 people in America1, is a chronic disease marked by insulin resistance. Insulin is a hormone that regulates blood sugar, so people with type 2 diabetes may have high blood sugar levels, which can lead to heart disease, vision loss, and kidney disease1. Diabetes is also linked to high inflammation levels

Researchers have long suspected that caffeine can help lower inflammation, but the team on this new study found that previous research on the topic had limitations and contradictory results.

Using data taken from two large-population studies (the UK-Biobank study and the Rotterdam study), they set out to understand the mechanisms behind the “well-established” association between higher caffeine consumption and lower type 2 diabetes risk.

The UK-Biobank study involved 502,536 people in the United Kingdom from 2006 to 2010, and it included follow-up data on participants in 2017. Its goal was to understand genetic and lifestyle influences on common diseases2. The Rotterdam study, which began in 1990, is ongoing in the Netherlands. The authors of the recent Clinical Nutrition Journal study looked at three Rotterdam study cohorts totaling 14,929 people from 1990 to 2006 and including follow-up data from 2015.

They chose these datasets for a few reasons. For starters, they both documented the coffee consumption habits of participants and had long follow-up periods. The UK-Biobank study was previously used in research that concluded that light to moderate coffee consumption (about half a cup to three cups daily) was associated with a lower risk of death3. Meanwhile, the Rotterdam study has been analyzed to better understand how coffee consumption could affect kidney function4. The UK-Biobank study participants drank an average of three to four cups of coffee per day, while the Rotterdam study participants drank between half a cup and two cups daily, on average.

Researchers had three goals as they analyzed this sweeping data: to find out how long-term habitual coffee drinking affects insulin resistance and type 2 diabetes, to understand the extent to which type 2 diabetes-related inflammation markers mediate the effects, and to see if and how the effects change by coffee type and whether a person smokes.

Their findings confirmed an association between higher habitual coffee consumption and a lower risk of type 2 diabetes and insulin resistance. Drinkers of ground (filtered or espresso) coffee were most likely to benefit, compared with people who drank instant or decaf coffee. Nonsmokers were also more likely to benefit than smokers.

The researchers came to that conclusion after finding that drinking coffee was associated with a lower concentration of inflammatory biomarkers, including C-reactive protein and leptin, and a higher concentration of anti-inflammatory biomarkers, like adiponectin and interleukin 13. 

They found that an increase in coffee consumption (drinking one additional cup of coffee every day) was associated with a 4% lower type 2 diabetes risk. However, the researchers added that more studies on inflammation biomarkers and coffee types are needed to confirm their findings.