Tea, Coffee May Protect Against Diabetes

Dec. 15, 2009— -- Drinking lots of coffee and tea every day -- even decaf -- might keep diabetes away, new research shows.

In a review of 18 studies, researchers found that drinking three to four cups of coffee per day was associated with a 25 percent lower risk of diabetes than drinking two cups or less per day, according to Dr. Rachel Huxley of the George Institute for International Health in Sydney, Australia, and her colleagues.

There were similar results for decaf coffee and tea.

"If such beneficial effects were observed in interventional trials to be real, the implications for the millions of individuals who have diabetes, or who are at future risk of developing it, would be substantial," the researchers concluded in the latest issue of the journal Archives of Internal Medicine.

Over the years, a variety of investigators have reported that coffee and tea consumption are inversely associated with type 2 diabetes. To sort out the data, Huxley and colleagues conducted a meta-analysis -- a review of past research -- that looked at 18 studies conducted between 1966 and July 2009 with information on 457,922 patients.

The researchers found that as coffee consumption rose, the risk of diabetes fell. Each additional cup of coffee consumed in a day was associated with a 7 percent reduction in the excess risk of diabetes.

The researchers said the results across studies were independent of effects involving gender, geographic region, or diagnosis versus self-reporting. Moreover, six of the studies reported on the association between drinking decaffeinated coffee and subsequent risk of diabetes.

A pooled summary estimated that those who drank more than three to four cups of decaf coffee per day had about a third lower risk of diabetes than those who didn't drink any decaf.

Seven studies also looked at the association between tea and diabetes risk. Again, pooled summaries showed that patients who drank more than three to four cups of tea per day had about a 20 percent lower risk of diabetes than those who drank no tea.

The researchers noted that the coffee findings may be an overestimate due to "small-study bias," and cautioned that any possibility that the association between coffee and diabetes risk is age-dependent warrants further investigation.

The findings suggest that the protective effects of tea and coffee may not be solely related to the effects of caffeine, but rather involve a broader range of chemical constituents in the drinks including magnesium, lignans, and chlorogenic acids, the researchers wrote. Substances in tea called catechins, for example, may decrease glucose production in the gastrointestinal system, leading to lower levels of glucose and insulin, and green tea in particular may prevent damage to pancreatic beta cells.