Article Text

Additive effects of green tea and coffee on all-cause mortality in patients with type 2 diabetes mellitus: the Fukuoka Diabetes Registry
  1. Yuji Komorita1,2,
  2. Masanori Iwase1,3,
  3. Hiroki Fujii1,
  4. Toshiaki Ohkuma1,
  5. Hitoshi Ide1,
  6. Tamaki Jodai-Kitamura1,
  7. Masahito Yoshinari1,
  8. Yutaro Oku1,
  9. Taiki Higashi1,
  10. Udai Nakamura1,
  11. Takanari Kitazono1
  1. 1Department of Medicine and Clinical Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan
  2. 2Division of Internal Medicine, Fukuoka Dental College, Fukuoka, Japan
  3. 3Diabetes Center, Hakujyuji Hospital, Fukuoka, Japan
  1. Correspondence to Dr Masanori Iwase; iwase{at}


Introduction The impact of consuming green tea or coffee on mortality in patients with diabetes is controversial. We prospectively investigated the impact of each beverage and their combination on mortality among Japanese patients with type 2 diabetes.

Research design and methods In all, 4923 patients (2790 men, 2133 women) with type 2 diabetes (mean age, 66 years) were followed prospectively (median, 5.3 years; follow-up rate, 99.5%). We evaluated the amount of green tea and coffee consumed using self-administered questionnaires.

Results During the follow-up period, 309 participants died. The consumption of green tea, coffee, and a combination of the beverages was associated with reduced all-cause mortality. Multivariable-adjusted hazard ratios (95% CIs) for green tea were as follows: none 1.0 (referent); 0.85 (0.60–1.22) for ≤1 cup/day; 0.73 (0.51–1.03) for 2–3 cups/day; 0.60 (0.42–0.85) for ≥4 cups/day; and P for trend, 0.002. For coffee, they were: none 1.0 (referent); 0.88 (0.66–1.18) for <1 cup/day; 0.81 (0.58–1.13) for 1 cup/day; 0.59 (0.42–0.82) for ≥2 cups/day; P for trend, 0.002. With the combination they were 1.0 (referent) for no consumption of green tea and coffee; 0.49 (0.24–0.99) for 2–3 cups/day of green tea with ≥2 cups/day of coffee; 0.42 (0.20–0.88) for ≥4 cups/day of green tea with 1 cup/day of coffee; and 0.37 (0.18–0.77) for ≥4 cups/day of green tea with ≥2 cups/day of coffee.

Conclusions Higher consumption of green tea and coffee was associated with reduced all-cause mortality: their combined effect appeared to be additive in patients with type 2 diabetes.

  • type 2 diabetes
  • nutritional epidemiology
  • mortality
  • green tea catechin

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  • Contributors YK and MI were responsible for the study concept and design. YK, MI, and HF conducted the analysis. TO, HI, TJ-K, MY, YO, TH, UN, and TK interpreted the data and contributed to the discussion. YK and MI drafted the manuscript. All authors participated in critically revising the manuscript and approved the final version. MI is the guarantor of this work and, as such, had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

  • Funding This work was supported in part by The Japan Society for the Promotion of Science KAKENHI from the Ministry of Education, Culture, Sports, Science and Technology of Japan (grant numbers 20K19663 to YK, 23249037 and 23659353 to MI, 16K00861 to HF, and 19K24229 to TO), the Junior Scientist Development Grant supported by the Japan Diabetes Society (to YK and TO), the Lilly Research Grant Program for Bone & Mineral Research (to YK), a grant from the Japan Diabetes Foundation (to TO), and the Japan Heart Foundation and Astellas/Pfizer Grant for Research on Atherosclerosis Update (to TO).

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Ethics approval The Kyushu University Institutional Review Board (approval number 290). All participants provided their written informed consent to take part.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.