Written by Joyce Smith, BS. Higher consumption of green tea and coffee was associated with increased longevity in a Japanese population with type 2 diabetes.
Diabetes has been increasing worldwide 1, and although its risk of vascular disease, dementia and cancers and its effect on quality of life and life expectancies are known, no studies on green tea and diabetes risk have been done to date. However, green tea from Camellia sinensis is rich in phenolic compounds, theanine and caffeine, and is known for its antioxidant, anti-inflammatory, and antibacterial properties 2,3 that help prevent chronic disease and reduce mortality 4. Coffee, which like green tea, is consumed worldwide, and also contains health-promoting phenolic compounds and caffeine that collectively demonstrate antioxidant, anti-inflammatory, and antimutagenic effects 5. Coffee has also been shown to increase blood pressure and the risk of heart attack 6; and the few studies that have investigated the effect of coffee consumption on mortality in diabetic patients, have shown controversial results. To date, no study has explored the combined effect of green tea and coffee consumption on all-cause mortality in diabetics, thus the present study was designed to investigate a potential association between the combined effect of higher green tea and coffee consumption and reduced mortality in Japanese tea drinkers with type 2 diabetes.
The Fukuoka Diabetes Registry is a multicenter prospective study (UMIN Clinical Trial Registry 000002627) designed to investigate the effect of modern treatments and lifestyles on the prognoses of patients with diabetes mellitus. 7 Of the 5,131 registered patients with diabetes mellitus, 4,923 were enrolled in the study. Participants were 20 years or older (average age 66) and were registered during regular visits between April 2008 and October 2010, A dietary survey, including green tea and coffee consumption, was conducted using a self-administered brief diet history questionnaire (Gender Medical Research Inc., Tokyo) regarding the frequency of 58 food items and supplements. Green tea and coffee consumption were self-reported. The amount of coffee and tea consumed per day was ascertained by selecting from 8 categories that quantified participants’ daily tea and coffee consumption. Since Japanese people do not drink decaffeinated beverages, there was no differentiation made between “caffeinated” and “decaffeinated” beverages.
Results showed that higher green tea and coffee consumption was significantly associated with decreased all-cause mortality in patients with type 2 diabetes. The association remained significant after adjusting for potential confounders. Analysis revealed the following:
- Drinking up to 1 cup of green tea every day was associated with 15% lower odds of death; while drinking 2-3 cups was associated with 27% lower odds and 4 or more daily cups was associated with 40% lower odds.
- For coffee drinkers, less than 1 cup/day was associated with 12% lower odds; 1 cup/day with 19% lower odds, 2 or more cups with 41% lower odds of death.
- Drinking both green tea and coffee every day further lowered the risk of death by 51% for drinkers of 2-3 cups of green tea plus 2 or more of coffee, by 58% for drinkers of 4 or more cups of green tea plus 1 cup of coffee every day, and by 63% for those who drank a combination of 4 or more cups of green tea and 2 or more cups of coffee every day.
- The analyzes of CVD-specific mortality revealed similar trends.
This observational study, could not establish causation, only an association. Self-assessment of green tea and coffee consumption was a source of bias. As well, potential confounders such as household income and level of education were overlooked. The exclusive Japanese population cannot be generalized to other ethnic groups. Finally, the green tea used in the study may be available only in Japan. In spite of these limitations, the study does suggest that consuming green tea and coffee may support the longevity of Japanese people with type 2 diabetes.
Source: Komorita, Yuji, Masanori Iwase, Hiroki Fujii, Toshiaki Ohkuma, Hitoshi Ide, Tamaki Jodai-Kitamura, Masahito Yoshinari et al. “Additive effects of green tea and coffee on all-cause mortality in patients with type 2 diabetes mellitus: the Fukuoka Diabetes Registry.” BMJ Open Diabetes Research and Care 8, no. 1 (2020): e001252.
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Posted November 24, 2020.
Joyce Smith, BS, is a degreed laboratory technologist. She received her bachelor of arts with a major in Chemistry and a minor in Biology from the University of Saskatchewan and her internship through the University of Saskatchewan College of Medicine and the Royal University Hospital in Saskatoon, Saskatchewan. She currently resides in Bloomingdale, IL.
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- Komorita Y, Iwase M, Fujii H, et al. Additive effects of green tea and coffee on all-cause mortality in patients with type 2 diabetes mellitus: the Fukuoka Diabetes Registry. BMJ open diabetes research & care. 2020;8(1).
