Coffee, tea can prevent diabetes

Drinking tea or coffee reduces the risk of diabetes, according to a review of 18 studies that covered hundreds of thousands of people. Previous research had shown that people who drank the most coffee were one-third less likely to develop diabetes than those who drank the least. In the years since then, the amount of research on coffee and diabetes risk has more than doubled, and other studies have suggested that tea and decaffeinated coffee may also be effective in preventing diabetes.

To update the evidence, researchers reviewed 18 studies on coffee (including decaffeinated coffee) and tea and the risk of type 2 diabetes published between 1966 and 2009 covering about 4.6 lakh people. It was found that for every additional cup of coffee a person consumed each day, a person's risk of diabetes was reduced by 7 percent.

In the six studies that looked at decaffeinated coffee, the researchers found that people who consumed more than three or four cups a day were at 36 percent lower risk of diabetes. And in seven studies that examined tea drinking and diabetes risk, people who drank more than three or four cups daily were at 18 percent lower diabetes risk.

The above analysis could have overestimated the effect of these beverages on diabetes risk due to statistical issues with the smaller studies. It's also not possible to conclude from the current evidence that heavy coffee drinkers (and tea and decaffeinated drinkers) don't have other characteristics that might protect them against developing diabetes such as eating a healthier diet.

The fact that the effects were seen with decaffeinated as well as coffee and tea suggest that if the effects are real, they aren't just due to caffeine, but may be related to other substances found in these beverages for example magnesium, lignans (oestrogen-like chemicals found in plants), or chlorogenic acids, which are antioxidants that slow the release of sugar into the blood after a meal.

However, further clinical trials are needed to investigate whether these beverages do indeed help prevent diabetes. If the benefits turn out to be real, health care providers might begin advising patients at risk for diabetes not only to exercise and lose weight, but to drink more tea and coffee, too.