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The Relationship between Green Tea and Total Caffeine Intake and Risk for Self-Reported Type 2 Diabetes among Japanese Adults
Hiroyasu Iso, MD; Chigusa Date, PhD; Kenji Wakai, MD; Mitsuru Fukui, PhD; Akiko Tamakoshi, MD, and the JACC Study Group*
18 April 2006 | Volume 144 Issue 8 | Pages 554-562
Background: In western populations, coffee consumption is associated with a reduced risk for type 2 diabetes; however, the effect of green, black, and oolong teas is unclear.
Objective: To examine the relationship between consumption of these beverages and risk for diabetes.
Design: Retrospective cohort study.
Setting: 25 communities across Japan.
Participants: A total of 17 413 persons (6727 men and 10 686 women; 49% of the original study population) who were 40 to 65 years of age; had no history of type 2 diabetes, cardiovascular disease, or cancer at the baseline lifestyle survey; and completed the 5-year follow-up questionnaire. There was no difference in body mass index levels at baseline between respondents and nonrespondents.
Measurements: Questionnaire on consumption of coffee; black, green, and oolong teas; and physician-diagnosed diabetes.
Results: During the 5-year follow-up, there were 444 self-reported new cases of diabetes in 231 men and 213 women (5-year event rates, 3.4% and 2.0%, respectively). Consumption of green tea and coffee was inversely associated with risk for diabetes after adjustment for age, sex, body mass index, and other risk factors. Multivariable odds ratios for diabetes among participants who frequently drank green tea and coffee (6 cups of green tea per day and 3 cups of coffee per day) were 0.67 (95% CI, 0.47 to 0.94) and 0.58 (CI, 0.37 to 0.90), respectively, compared with those who drank less than 1 cup per week. No association was found between consumption of black or oolong teas and the risk for diabetes. Total caffeine intake from these beverages was associated with a 33% reduced risk for diabetes. These inverse associations were more pronounced in women and in overweight men.
Limitations: Diabetes was self-reported, no data were available on consumption of soda, and the follow-up rate was low.
Conclusions: Consumption of green tea, coffee, and total caffeine was associated with a reduced risk for type 2 diabetes.
*For members of the JACC Study Group, see the Appendix.
Editors’ Notes
Context
Caffeine intake from coffee has been associated with a lower incidence of diabetes. Researchers have not studied the relationship of green tea, a popular beverage in Japan, where the incidence of diabetes is increasing rapidly.
Contributions
The authors estimated the intake of caffeine-containing beverages in a community-based survey in Japan and measured the 5-year incidence of diabetes. Greater intake of green tea or coffee was associated with a reduced incidence of diabetes. The effect of green tea was largely observed in women, was dose-related, and reflected caffeine intake.
Implications
Higher intake of caffeine, whether from coffee or green tea, is associated with a lower incidence of diabetes.
—The Editors
Author and Article Information
From Osaka University and Osaka City University, Osaka, Japan; Nara Women’s University, Nara, Japan; and Aichi Cancer Center and Nagoya University, Nagoya, Japan.
Acknowledgments: The authors thank Dr. Kunio Aoki, Professor Emeritus, Nagoya University School of Medicine and former chairman of the JACC Study Group; Dr. Haruo Sugano, former director of the Cancer Institute of the Japanese Foundation for Cancer Research, who greatly contributed to the initiation of the study; and Professor Aaron R. Folsom, University of Minnesota, for valuable scientific suggestions.
Grant Support: The JACC Study has been supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan (61010076, 62010074, 63010074, 1010068, 2151065, 3151064, 4151063, 5151069, 6279102, and 11181101).
Potential Financial Conflicts of Interest: None disclosed.
Requests for Single Reprints: Hiroyasu Iso, MD, Public Health, Department of Social and Environmental Health, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-shi, Osaka 565-0871, Japan; e-mail, iso@pbhel.med.osaka-u-ac.jp.
Current Author Addresses: Dr. Iso: Public Health, Department of Social and Environmental Health, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita-shi, Osaka 565-0871, Japan.
Dr. Date: Nara Women’s University, Kitauoyanishi-machi, Nara 630-8506, Japan.
Dr. Wakai: Aichi Cancer Center, 1-1 Kanokoden, Chikusan-ku, Nagoya 466-8681, Japan.
Dr. Fukui: Osaka City University, 1-4-3 Asahi-machi, Abeno-ku, Osaka 545-8585, Japan.
Dr. Tamakoshi: Nagoya University, 65 Tsurumai-cho, Showa-ku, Nagoya, Aichi 466-8550, Japan.
Author Contributions: Conception and design: H. Iso.
Analysis and interpretation of the data: H. Iso.
Drafting of the article: H. Iso.
Critical revision of the article for important intellectual content: H. Iso, C. Date, K. Wakai, M. Fukui, A. Tamakoshi.
Final approval of the article: H. Iso, C. Date, K. Wakai, M. Fukui, A. Tamakoshi.
Provision of study materials or patients: The JACC Study Group.
Statistical expertise: H. Iso, K. Wakai, M. Fukui.
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