type 2 diabetes
Coffee consumption and type 2 diabetes
Coffee and risk of type 2 diabetes
In 2002, a Dutch cohort study of 17,111 adults identified 306 new cases of type 2 diabetes and 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, more than a dozen other studies have confirmed this finding in other populations.
At the end of 2009, a group of expert researchers published a systematic review with meta-analysis of the available prospective epidemiological studies on type 2 diabetes and coffee, decaffeinated coffee and tea consumption6. This meta-analysis covered 457,922 individuals and 21,897 newly diagnosed cases of type 2 diabetes from eight different countries (eight studies from the USA, four from Finland, two from the Netherlands, two from Japan and one study each from Sweden, Singapore, Puerto Rico and the UK).
The combined data showed a statistically significant negative association between coffee consumption and subsequent risk of type 2 diabetes. 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 this review with meta-analysis, eight more epidemiological studies have been published7,8,9,10,11,12,13,14. All eight (three studies from the USA, and one study each from the Netherlands, Norway, France, China and Japan) confirmed the inverse association with coffee consumption.
Taking the meta-analysis with its included studies6 and these recent ones together, almost all 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 diabetes6.
Two further review papers, both published in 2012, add to the existing body of evidence suggesting that habitual coffee consumption is associated with a lower risk of type 2 diabetes15,16.
Decaffeinated coffee and tea and risk of type 2 diabetes
As with caffeinated coffee, the majority of published studies which have evaluated the relationship between decaffeinated coffee or tea drinking and risk of type 2 diabetes have reported similar negative associations.
In the 2009 meta-analysis, similar statistically significant negative associations were found for the consumption of decaffeinated coffee and tea and risk of type 2 diabetes6.
The large US study with African-American women11 and the French study9, also looked at the association for decaffeinated coffee. One of the two confirmed an association9, the other one did not see a correlation11.
Five of the epidemiological studies also looked at tea consumption7,8,10,11,12. Two confirmed the negative association8,12. The other three did not observe an association for tea consumption7,10,11.