Previous studies in the United States and Europe have linked coffee to a reduced risk of type 2 diabetes, according to background information in the article. The link between coffee and diabetes risk appears to be consistent across different ages and body weights; in addition, most research has found that the more coffee an individual generally drinks, the lower his or her risk for diabetes. However, it remains unclear whether it is the caffeine or another ingredient in coffee that may confer a protective effect.
Mark A. Pereira, Ph.D., and colleagues at the University of Minnesota, Minneapolis, studied coffee intake and diabetes risk in 28,812 postmenopausal women in Iowa over an 11-year period. At the beginning of the study, in 1986, the women answered questions about their risk factors for diabetes, including age, body mass index, physical activity, alcohol consumption and smoking history. They also reported how often they consumed a variety of foods and beverages over the previous year, including regular and decaffeinated coffee.
Based on information reported in the initial questionnaire, about half of the women (14,224) drank one to three cups of coffee per day; 2,875 drank more than six cups; 5,554 four to five cups; 3,231 less than one cup; and 2,928 none. Over the following 11 years, 1,418 of the women reported on surveys that 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 six cups of any type of coffee per day were 22 percent less likely than those who drank no coffee to be diagnosed with diabetes; those who drank more than six cups of decaffeinated coffee per day had a 33 percent reduction in risk compared with those who drank none.
Overall caffeine intake did not appear to be related to diabetes risk, further suggesting that some other ingredient in coffee was responsible. "Magnesium, for which coffee is a good source, could explain some of the inverse association between coffee intake and risk of type 2 diabetes mellitus through known beneficial effects on carbohydrate metabolism," the authors write. However, the study found no association between this mineral and diabetes risk. Other minerals and nutrients found in the coffee bean--including compounds known as polyphenols that have also been shown to help the body process carbohydrates and antioxidants that may protect cells in the insulin-producing pancreas--may contribute to its beneficial effects and should be examined in future studies.
"In summary, we observed an inverse association between coffee consumption, especially decaffeinated coffee consumption, and the risk of type 2 diabetes mellitus over an 11-year period in postmenopausal women residing in the state of Iowa," the authors conclude. "Although the first line of prevention for diabetes is exercise and diet, in light of the popularity of coffee consumption and high rates of type 2 diabetes mellitus in older adults, these findings may carry high public health significance."