Caffeinated and decaffeinated coffee consumption and risk of type 2 diabetes: a systematic review and a dose-response meta-analysis

Abstract

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.

Figure 1

Study selection process of the identified articles.

Figure 2

Forest plot of the associations between total coffee consumption and risk of type 2 diabetes. Compared with the lowest category (median consumption 0 cups/day), the pooled RR for incident type 2 diabetes was 0.70 (95% CI 0.65–0.75, I² = 50%, P for heterogeneity = 0.001) for the highest category of consumption, 0.80 (0.75–0.85, I² = 71%, P < 0.001) for the second highest, and 0.91 (0.88–0.94, I² = 19%, P = 0.17) for the third highest category of coffee consumption.

Figure 3

Dose-response analysis of the association between coffee consumption and risk of type 2 diabetes. For the overall association between coffee consumption and risk of diabetes, P < 0.001; for the goodness of fit of the model, P = 0.14; and for the likelihood ratio test compared with the nested linear model, P < 0.001.