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. 2018 Dec 27;11(1):48.
doi: 10.3390/nu11010048.

Effects of Coffee and Tea Consumption on Glucose Metabolism: A Systematic Review and Network Meta-Analysis

Yoshinobu Kondo  1 , Atsushi Goto  2 , Hisashi Noma  3 , Hiroyasu Iso  4 , Kunihiko Hayashi  5 , Mitsuhiko Noda  6
Affiliations

Effects of Coffee and Tea Consumption on Glucose Metabolism: A Systematic Review and Network Meta-Analysis

Yoshinobu Kondo et al. Nutrients. .

Abstract

Prospective cohort studies have described an association between coffee or tea consumption and the risk of developing diabetes. However, whether coffee or tea improves glucose metabolism remains uncertain. We investigated the effect of coffee and tea on glucose metabolism by conducting a systematic review and meta-analysis of randomized controlled trials. Electronic databases were searched for articles published up 19 February 2017. The primary endpoint was the mean difference in post-intervention fasting blood glucose (FBG) levels between the groups. Of 892 citations screened, 27 studies (1898 participants) were included in our meta-analysis. A network meta-analysis suggested that green tea, but not caffeinated/decaffeinated coffee or black tea, may reduce FBG levels, compared with placebo/water (-2.10 mg/dL; 95% confidence interval (CI), -3.96 to -0.24 mg/dL; p = 0.03; moderate quality of evidence). In a subgroup analysis, the effect of green tea on FBG levels was statistically significant only in studies with a mean age of < 55-years-old or Asian-based studies. The oolong tea group also showed a significant decrease in FBG, but the quality of evidence was very low. In conclusion, green tea consumption might decrease FBG levels, especially in < 55-year-olds or Asian-based populations.

Keywords: coffee; fasting blood glucose; glucose metabolism; network meta-analysis; tea.

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Conflict of interest statement

All authors have no potential conflict of interest.

Figures

Figure 1
Figure 1
Study selection flow.
Figure 2
Figure 2
Network maps. (A) Fasting blood glucose; (B) 2-h post-load glucose concentration from an oral glucose tolerance test; (C) HbA1c; (D) fasting blood insulin; (E) HOMA-IR; Nodes represent the interventions and their sizes represent the number of participants. Edges represent the available direct comparisons between pairs of interventions; the width represents the number of studies comparing the pair of interventions. Abbreviations: Decaf, decaffeinated; PLC, placebo.
Figure 3
Figure 3
Risk of bias summary.
Figure 4
Figure 4
Direct pairwise meta-analysis of effects on fasting blood glucose levels. c, coffee study arm; d, decaffeinated coffee study arm.
Figure 5
Figure 5
Direct pairwise meta-analysis: effects of green tea on fasting blood glucose levels stratified by Asian-based studies and non-Asian based studies.
See this image and copyright information in PMC

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