Coffee, tea and diabetes: the role of weight loss and caffeine

OBJECTIVE: To assess the effect of weight change on the relationship between coffee and tea consumption and diabetes risk. DESIGN: Prospective cohort study, using data from the First National Health and Nutrition Examination Survey Epidemiologic Follow Up Study. Survival analyses were conducted using 301 selfreported cases of diabetes and eight documented diabetes deaths during an 8.4-y follow-up. SUBJECTS: A total of 7006 subjects aged 32-88 y with no reported history of diabetes were included in the study. RESULTS: For all subjects combined, increases in consumption of ground-caffeinated coffee and caffeine at baseline were followed by decreases in diabetes risk during follow-up. There were significant statistical interactions between age and consumption of caffeine (P = 0.02) and ground-caffeinated coffee (P = 0.03). Age-stratified analysis showed that the decrease in diabetes risk only applied to <= 60-y-old subjects, for whom the decrease in diabetes risk also obtained for ground-decaffeinated coffee and regular tea. The multivariate hazard ratio (HR) and 95% confidence interval for a 2 cups/day increment in the intake of ground-caffeinated coffee, ground-decaffeinated coffee and regular tea was 0.86 (0.75-0.99), 0.58 (0.34-0.99) and 0.77 (0.59-1.00), respectively. The diabetes risk was negatively related to the consumption in a dose-response manner. There were strong statistical interactions between prior weight change and beverage consumption for <= 60-y-old subjects. Further analysis revealed that the decrease in diabetes risk only applied to those who had lost weight, and that there was a positive dose response relationship between diabetes risk and weight change. For example, the multivariate HR and 95% confidence interval for 40 vs 0 cups/day of ground-decaffeinated coffee was 0.17 (0.04-0.74), 0.52 (0.19-1.42), 0.77 (0.30-1.96) and 0.91 (0.39-2.14)for subgroups with weight change of <= 0, 0-10, 10-20 and > 20 lbs, respectively. There was no significant association between diabetes risk and consumption of instant-caffeinated coffee, instant-decaffeinated coffee or herbal tea. Caffeine intake appeared to explain some, but not all, of the diabetes-risk reduction and weight change. CONCLUSION: The negative relationship between diabetes risk and consumption of ground coffee and regular tea, observed for all NHEFS subjects, actually only applied to nonelderly adults who had previously lost weight.