Green tea, coffee consumption may cut mortality risk in type 2 diabetes
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Japanese adults with type 2 diabetes who drank more green tea and coffee were less likely to die of any cause during 5 years of follow-up; the combined effect of the two beverages appeared to be additive, study data show.
“Green tea and coffee, and their combined consumption habits, may improve the prognosis of people with diabetes,” Yuji Komorita, MD, PhD, specially appointed assistant professor in the department of medicine and clinical science at Kyushu University Graduate School of Medical Sciences in Fukuoka, Japan, told Healio. “However, because this study is observational, it is important to note that simply drinking green tea and coffee does not extend your life span.”
In a study published in BMJ Open Diabetes Research & Care, Komorita and colleagues analyzed data from 4,923 adults with type 2 diabetes (2,790 men; mean age, 66 years) followed prospectively for a median of 5.3 years. Researchers evaluated the amount of green tea and coffee consumed using self-administered questionnaires. During the follow-up, 309 participants died.
Researchers found that drinking green tea, coffee and a combination of the beverages was associated with reduced all-cause mortality. Compared with participants who reported drinking no green tea, the HR for those who consumed at least 1 cup was 0.85 (95% CI, 0.6-1.22), with the HR falling to 0.73 for those who consumed 2 to 3 cups per day (95% CI, 0.51-1.03) and 0.6 for those who consumed at least 4 cups per day (95% CI, 0.42-0.85).
For coffee, the HR for all-cause mortality for participants who reported drinking at least 2 cups per day was 0.59 (95% CI, 0.42-0.82) compared with those who did not drink coffee.
The greatest reduction in all-cause mortality was observed among participants who reported drinking both green tea and coffee. Compared with those who drank neither, those who consumed 2 to 3 cups of green tea plus at least 2 cups of coffee daily were half as likely to die of any cause during follow-up (HR = 0.49; 95% CI, 0.24-0.99), whereas those who drank at least 4 cups of green tea and 1 cup of coffee per day were 63% less likely to die during follow-up compared with those who did not drink either beverage (HR = 0.37; 95% CI, 0.18-0.77).
“Since patients with diabetes have higher risk for cardiovascular disease, caffeine in coffee or green tea has been thought to be harmful for them, although there have been few studies to investigate it,” Komorita said. “This study is one of the positive studies to show the beneficial aspect of these beverages, and can be a clue to expand the diet treatment of diabetes.”
Komorita cautioned that the study was observational and more research is needed on a dose-response effect and which patients could derive the greatest benefit from tea and coffee consumption.
“Furthermore, this study does not have information about education, income or the family background of participants, which may have been confounded,” Komorita said. “Additionally, because some patients may consume too much caffeine, further study is needed to identify which patients derive benefit.”
For more information:
Yuji Komorita, MD, PhD, can be reached at yjkmrt@intmed2.med.kyushu-u.ac.jp; Twitter: @yjkom.
Perspective
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Susan Burke March, MEd, RDN, LD/N, CDE
The conclusions of this study demonstrate how difficult it is to perform studies on specific foods or nutrients and extrapolate the results to policy or guidelines for health. The authors do a good job of citing the research that links coffee and green tea consumption to health benefits and the substances that have been shown to be healthy, and at the same time note that, for some, these same substances may be harmful. For those with cardiovascular disease, for example, increased caffeine is associated with increased risk for hypertension.
Based on this study of Japanese adults with type 2 diabetes, it appears that consuming both coffee and green tea can be beneficial, but not in a "curative" way. There are eight limitations that are mentioned in this study, and I won't review them all here, but they are significant. The scientists only conclude that this study "suggests" a beneficial effect in type 2 diabetes.
I would advise my patients, regardless of their medical conditions, that it is their total diet and lifestyle that are protective against disease. This study is interesting and suggests that the biochemicals in coffee and green tea may be protective; however, they are only protective when you take the other known steps that contribute to strong immunity. Those steps include eating a plant-based diet, avoiding processed foods as much as possible, exercising daily, managing stress, getting sufficient sleep, not smoking, and yes, enjoying coffee and tea in moderation — not with cream and sugar — early in the day, as caffeine is known to interfere with sleep.
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