Background: In western populations, coffee consumption is associated with a reduced risk for type 2 diabetes; however, the effect of green, black, and oolong teas is unclear.
Objective: To examine the relationship between consumption of these beverages and risk for diabetes.
Design: Retrospective cohort study.
Setting: 25 communities across Japan.
Participants: A total of 17,413 persons (6727 men and 10,686 women; 49% of the original study population) who were 40 to 65 years of age; had no history of type 2 diabetes, cardiovascular disease, or cancer at the baseline lifestyle survey; and completed the 5-year follow-up questionnaire. There was no difference in body mass index levels at baseline between respondents and nonrespondents.
Measurements: Questionnaire on consumption of coffee; black, green, and oolong teas; and physician-diagnosed diabetes.
Results: During the 5-year follow-up, there were 444 self-reported new cases of diabetes in 231 men and 213 women (5-year event rates, 3.4% and 2.0%, respectively). Consumption of green tea and coffee was inversely associated with risk for diabetes after adjustment for age, sex, body mass index, and other risk factors. Multivariable odds ratios for diabetes among participants who frequently drank green tea and coffee (> or =6 cups of green tea per day and > or =3 cups of coffee per day) were 0.67 (95% CI, 0.47 to 0.94) and 0.58 (CI, 0.37 to 0.90), respectively, compared with those who drank less than 1 cup per week. No association was found between consumption of black or oolong teas and the risk for diabetes. Total caffeine intake from these beverages was associated with a 33% reduced risk for diabetes. These inverse associations were more pronounced in women and in overweight men.
Limitations: Diabetes was self-reported, no data were available on consumption of soda, and the follow-up rate was low.
Conclusions: Consumption of green tea, coffee, and total caffeine was associated with a reduced risk for type 2 diabetes.