Coffee consumption and type 2 diabetes

Coffee and risk of type 2 diabetes

One of the earlier studies into associations between coffee consumption and type 2 diabetes was a 2002 Dutch cohort study of 17,111 adults, which showed that those subjects drinking at least 7 cups of coffee per day were half as likely to develop type 2 diabetes⁵. This association was statistically significant. Since then, many other studies have confirmed this finding in other populations.

A 2009 systematic review with a meta-analysis of 457,922 individuals and 21,897 newly-diagnosed cases of type 2 diabetes from eight different countries considered a dose response effect⁶. The study showed a statistically significant negative association between coffee consumption and subsequent risk of type 2 diabetes, and the dose response analysis concluded that every additional cup of coffee, up to 6-8 cups per day, was associated with a 5-10% lower risk of developing type 2 diabetes. Drinking 3-4 cups of coffee per day was associated with an approximate 25% lower risk of developing type 2 diabetes, compared to consuming none or less than 2 cups per day.

Since then, a number of epidemiological studies and reviews published from different countries have also confirmed the inverse association with coffee consumption^7-16.

Adding to the body of data, a 2013 multiethnic cohort study suggested that caffeinated (but not decaffeinated) coffee consumption was much more protective against diabetes in women of all ethnic groups than in men, where the relationship was borderline¹⁷.

Further dose response reviews have also been undertaken. A 2014 study concluded that participants who increased coffee intake by more than one cup per day over a 4 year period had an 11% lower risk of type 2 diabetes, whilst those who decreased coffee consumption by one cup per day had a 17% greater risk of type 2 diabetes¹⁸. Additionally, a 2014 review suggested a 12% reduction in risk of type 2 diabetes for every additional two cups of coffee per day, and a 14% reduction for every 200mg increment of caffeine per day.  This review also suggested that the effect was stronger for women than men¹⁹. A further 2014 review also concluded that the risk of diabetes was reduced by, respectively: 8, 15, 21, 25, 29 and 33% for 1-6 cups of coffee per day²⁰.

The significance of long-term habitual coffee drinking against diabetes onset was highlighted in a 10 year follow-up study from Greece²¹.

A 2016 review supported earlier research, concluding that there is mounting evidence for a reduced risk of type 2 diabetes in those who regularly drink 3-4 cups of coffee per day²².

Taking all the research together, almost all studies reported a statistically significant negative association for coffee consumption and type 2 diabetes. This similar observation in different populations, plus the dose response relation (lower incidence at higher consumption), are strong indications for a true association between consumption of coffee and the lower incidence of type 2 diabetes, with every additional cup of coffee, up to 6-8 cups per day, being associated with a 5-10% lower risk of developing type 2 diabetes^6,19,20.

Decaffeinated coffee and tea and risk of type 2 diabetes

As with caffeinated coffee, the majority of published studies that have evaluated the relationship between decaffeinated coffee or tea drinking and risk of type 2 diabetes have reported similar negative associations.

In a 2009 meta-analysis, similar statistically significant negative associations were found for the consumption of decaffeinated coffee and tea and risk of type 2 diabetes⁶.

A French study⁹ and a large US study with African-American women¹¹, also looked at the association for decaffeinated coffee. One of the two studies confirmed an association⁹; the other did not see a correlation¹¹. Additionally, a 2014 review concluded that in addition to an effect with caffeinated coffee, an 11% reduction for every 2 additional cups of decaffeinated coffee a day was also observed¹⁹.

Five of the epidemiological studies also looked at tea consumption^7,8,10,11,12. Two confirmed the negative association^8,12. The other three did not observe an association for tea consumption^7,10,11.