Does coffee help prevent type 2 diabetes?

Three to four cups of coffee a day is associated with a lower risk of type 2 diabetes. This emerges from several large population studies and a Mendelian randomisation study, in which genetic variants are used to approximate causality. The relationship is consistent, but still largely observational: we see an association, but cannot yet say with certainty that coffee is the cause.

Notably, decaffeinated coffee shows a similarly protective pattern. This suggests that caffeine is not the only active compound. Chlorogenic acids, a group of antioxidants found in coffee beans, are considered a possible explanation. Exactly how that mechanism works in humans has not yet been fully established.

For the average adult, three to four cups a day appears to be safe. There is little indication of health risks at that level of consumption. An interesting side finding: genetic research also suggests that coffee lovers have a lower chance of developing gallstones, which is relevant because type 2 diabetes itself increases the risk of gallstone disease.

Bear in mind that this is not evidence that coffee cures or treats type 2 diabetes. It is solely about prevention: people who already drink a lot of coffee appear to have a lower chance of developing the disease. Whether you should deliberately drink more coffee for preventive purposes is not something that can be concluded from studies of this kind.