New research published in Diabetologia, the journal of the European Association for the Study of Diabetes, shows that increasing coffee consumption by on average one and half cups per day (about 360 milliliters) over a four-year period reduces the risk of type 2 diabetes by 11 percent. The research is led by Frank Hu and Shilpa Bhupathiraju, Department of Nutrition, Harvard School of Public Health, Harvard University, and colleagues.
Coffee and tea consumption has been associated with a lower type 2 diabetes risk but little is known about how changes in coffee and tea consumption influence subsequent type 2 diabetes risk. The authors examined the associations between four-year changes in coffee and tea consumption and risk of type 2 diabetes in the subsequent four years.
The authors used observational data from three large prospective, US-based studies in their analysis: the Nurses’ Health Study of female nurses aged 30-55 years in 1986 to 2006, the Nurse Health Study II of younger female nurses aged 25 to 42 years in 1991 to 2007, and the Health Professionals Follow-up Study of male professionals 40 to 75 years in 1986 to 2006. Detailed information on diet, lifestyle, medical conditions, and other chronic diseases was collected every two to four years for over 20 years.
The availability of these repeated measures and the long-duration of follow-up allowed the authors to evaluate four-year changes in coffee and tea intake in relation to risk of type 2 diabetes in the following four years. They also examined whether the association with diabetes incidence differed between changes in caffeinated and decaffeinated
coffee. Diet was assessed every four years using a validated food frequency questionnaire. Self-reported incident type 2 diabetes cases were validated by supplementary questionnaires. The final analysis included 48,464 women in the first study, 47,510 women in the second study and 27,759 men in the third.
The authors documented 7,269 incident type 2 diabetes cases, and found that participants who increased their coffee consumption by more than one cup a day over a four-year period had a 11 percent lower risk of type 2 diabetes in the subsequent four years compared to those who made no changes in consumption. Participants who decreased their coffee intake by one cup a day or more had a 17 percent higher risk for type 2 diabetes. Changes in tea consumption were not associated with type 2 diabetes risk.
Those with highest coffee consumption and who maintained that consumption, referred to as “high-stable consumers” since they consumed three cups or more per day, had the lowest risk of type 2 diabetes, 37 percent lower than the low-stable consumers who consumed one cup or less per day.
The authors say that the higher risk of type 2 diabetes associated with decreasing coffee intake may represent a true change in risk, or may potentially be due to reverse causation whereby those with medical conditions associated with risk for type 2 diabetes, such as high blood pressure, elevated cholesterol, cardiovascular disease, cancer, may reduce their coffee consumption after diagnosis. However, even when cases of cardiovascular disease or cancer were excluded during follow-up, the results were very similar.