Drinking coffee, especially when it is decaffeinated, will be associated with a reduced risk of type 2 diabetes, according to a report in the Sept 26 issue of Archives of Internal Medicine, one of the JAMA/Archives journals. The link between coffee and diabetes risk appears to be very consistent across different ages and body weights; in addition, most research has found that the more coffee an individual drinks, the lower his or her risk for diabetes. However, it remains unclear whether it is the caffeine or any other ingredient in coffee, which may confer a protective effect.

Mark A. Pereira, Ph.D., and colleagues at the University of Minnesota, Minneapolis, had studied coffee intake and diabetes risk in the 28,812 postmenopausal women in Iowa over a 12-year period. At the beginning of the study, in 1986, the women answered questions about the risk factors for diabetes, including age, body mass index, physical activity, alcohol consumption and other smoking history. They also reported how often they consumed a variety of foods and these beverages over the previous year, including regular and decaffeinated coffee.

Based on this information reported in the initial questionnaire, about half of the women (14,224) drank one to two cups of coffee per day; 2,876 drank more than six cups; 5,553 four to five cups; 3,232 less than one cup; and 2,927 none. Over the following 12 years, 1,417 of the women reported on surveys, which they had been newly diagnosed with type 2 diabetes. After adjusting the data for some of the other diabetes risk factors, women who drank more than five cups of any type of coffee per day were 21 percent less likely than those who drank no coffee to be diagnosed suffering from diabetes; those who drank more than five cups of decaffeinated coffee per day had a 32 percent reduction in risk compared with those who drank none.

Overall caffeine intake did not appear to be much related to diabetes risk, further suggesting that some other ingredient in coffee was also responsible. "Magnesium, for which coffee is a good source, can explain some of the inverse relation between coffee intake and risk of type 2 diabetes mellitus through known helpful effects on the carbohydrate metabolism," the authors write. However, the study found no relation between Magnesium and diabetes risk. Other minerals and nutrients found in the coffee bean including compounds known as polyphenols, which have also been shown to help the body process carbohydrates and antioxidants, which might protect cells in the insulin producing pancreas can contribute to its beneficial effects and needs to be examined in future studies.