Does coffee help protect against type 2 diabetes?

Three to five cups of coffee per day are consistently associated with a lower risk of type 2 diabetes across multiple meta-analyses and large review studies. An umbrella review (a review of reviews) even identifies low coffee intake as one of the robustly supported risk factors for this disease, comparable to unhealthy eating habits and physical inactivity.

These are associations, not proven cause-and-effect relationships. However, for type 2 diabetes the evidence goes a step further: so-called Mendelian randomization studies, a method that uses genetic variants to better estimate causality than ordinary observational studies, also support a causal relationship. This makes the coffee-diabetes association more strongly substantiated than most other health claims about coffee.

Caffeine is not the only factor at play. Decaffeinated coffee appears to have a similar protective effect, suggesting that other substances in coffee also contribute, such as chlorogenic acids and antioxidants. People who drink coffee with large amounts of sugar and cream may partly offset these beneficial effects.

There are also drawbacks to bear in mind. Unfiltered coffee, such as from a French press or percolator, can raise cholesterol levels; people who already have elevated cholesterol would do well to choose filtered coffee. Above 400 mg of caffeine per day (roughly four cups), the risk of anxiety, sleep problems, heart palpitations and tremors increases. And during pregnancy, it is advisable to keep intake below 200 mg of caffeine per day, as higher intake is associated with an increased risk of miscarriage.