Abstract and Introduction
Objective Previous meta-analyses identified an inverse association of coffee consumption with the risk of type 2 diabetes. However, an updated meta-analysis is needed because new studies comparing the trends of association for caffeinated and decaffeinated coffee have since been published.
Research design and methods PubMed and Embase were searched for cohort or nested case-control studies that assessed the relationship of coffee consumption and risk of type 2 diabetes from 1966 to February 2013. A restricted cubic spline random-effects model was used.
Results Twenty-eight prospective studies were included in the analysis, with 1,109,272 study participants and 45,335 cases of type 2 diabetes. The follow-up duration ranged from 10 months to 20 years. Compared with no or rare coffee consumption, the relative risk (RR; 95% CI) for diabetes was 0.92 (0.90–0.94), 0.85 (0.82–0.88), 0.79 (0.75–0.83), 0.75 (0.71–0.80), 0.71 (0.65–0.76), and 0.67 (0.61–0.74) for 1–6 cups/day, respectively. The RR of diabetes for a 1 cup/day increase was 0.91 (0.89–0.94) for caffeinated coffee consumption and 0.94 (0.91–0.98) for decaffeinated coffee consumption (P for difference = 0.17).
Conclusions Coffee consumption was inversely associated with the risk of type 2 diabetes in a dose-response manner. Both caffeinated and decaffeinated coffee was associated with reduced diabetes risk.
Type 2 diabetes is a chronic disease with high rates of morbidity and mortality. The worldwide prevalence of type 2 diabetes is increasing, and the global number of people with diabetes is estimated to reach 366 million by the year 2030. The risk of blindness, renal disease, and amputation among those with type 2 diabetes is 20 to 40 times higher than that of people without diabetes. Furthermore, those with type 2 diabetes have a two to five times higher risk of myocardial infarction and two to three times higher risk of stroke. Given its significant burden, identifying modifiable lifestyle factors is imperative for the prevention of diabetes.
Coffee is one of the most widely consumed beverages around the world; thus, investigating its association with various diseases has important public health implications. An inverse association between coffee consumption and risk of type 2 diabetes was first reported in a Dutch population. In subsequent years, this finding has been confirmed in most[4–10] but not all[11–13] studies. Two previous meta-analyses of coffee consumption and risk of type 2 diabetes have been published. van Dam and Hu included nine cohort studies and reported a lower risk of type 2 diabetes for high coffee consumption compared with no coffee consumption with little between-study heterogeneity. Huxley et al. included 18 prospective studies and found an inverse monotonous association between the number of cups of coffee consumed and diabetes risk, but they double-counted data from the same cohort.[16,17] Since the publication of these meta-analyses, 10 additional prospective studies on the association between coffee consumption and diabetes have been published.[6,8,10,12,18–23]
A key issue that remains to be resolved is whether consumption of caffeinated and decaffeinated coffee is similarly associated with the risk of type 2 diabetes. Such results would provide insight into the role of caffeine in the putative relationship between coffee consumption and diabetes risk. The meta-analysis by Huxley et al. included only six studies on decaffeinated coffee, and estimates were less precise than for caffeinated coffee because of lower consumption levels. Eight subsequent prospective studies evaluated the association with decaffeinated coffee, approximately doubling the amount of data on decaffeinated coffee and diabetes risk.[8,10,12,18–21,24] We therefore performed an updated systematic review and a dose-response meta-analysis of all available data on the association of both caffeinated and decaffeinated coffee consumption with the risk of type 2 diabetes.
Diabetes Care. 2014;37(2):569-586. © 2014 American Diabetes Association, Inc.