Three to four cups a day appeared to offer some protection
Tea and coffee drinkers have a lower risk of developing type 2 diabetes, a large body of evidence shows.
And the protection may not be down to caffeine since decaf coffee has the greatest effect, say researchers in Archives of Internal Medicine.
They looked at 18 separate studies involving nearly 500,000 people.
This analysis revealed that people who drink three or four cups of coffee or tea a day cut their risk by a fifth or more, say researchers.
The same amount of decaffeinated coffee had an even bigger effect, lowering risk by a third.
Type 2 diabetes usually starts after the age of 40 and develops when the body can still make some insulin, but not enough, or when the insulin that is produced does not work properly. Type 2 diabetes is treated with a healthy diet and increased physical activity. In addition to this, medication and/or insulin is often required.
If the findings prove true, doctors may well start advising people to put the kettle on as well as take more exercise and watch their weight, say the researchers.
When the authors combined and analysed the data, they found that each additional cup of coffee consumed in a day cut diabetes risk by 7%.
Lead researcher Dr Rachel Huxley, from the University of Sydney in Australia, said because of the finding with decaffeinated coffee, the link is unlikely to be solely related to caffeine.
Instead, other compounds in coffee and tea - including magnesium and antioxidants known as lignans or chlorogenic acids - may be involved.
"The identification of the active components of these beverages would open up new therapeutic pathways for the primary prevention of diabetes mellitus.
"If such beneficial effects were observed in interventional trials to be real, the implications for the millions of individuals who have diabetes mellitus, or who are at future risk of developing it, would be substantial."
Dr Victoria King, of Diabetes UK, said: "Without full information about what other factors may be influencing the type 2 diabetes risk of the studies' participants - such as their physical activity levels and diet - as well as what the active ingredient in tea or coffee appears to be, we cannot be sure what, if anything, this observed effect is down to.
"What we can be sure of is that the development of type 2 diabetes is strongly linked to lifestyle, which means that many cases could be prevented by keeping active and eating a healthy balanced diet that is low in fat, salt and sugar with plenty of fruit and vegetables."