Green Tea and Diabetes

Why Green Tea?

            A healthy drink for you to enjoy, green tea is packed full of thousands of antioxidants and polyphenols. Polyphenols are beneficial molecules found in plants that have health benefits and prevent disease. One particularly potent polyphenol is catechin [1]. Catechins’ benefits are enhanced by the other components found in green tea.

Green Tea for Diabetes

Catechins neutralize free radicals. Left unchecked, free radicals cause inflammation and damage insulin receptors. Catechins also activate extra receptors on cells that bind insulin. These two actions help improve insulin sensitivity [2].

Extra sugar in your blood stream can build up on cell walls. Most complications of diabetes such as kidney failure, heart disease, neuropathy, (damage to your nerves) and retinopathy (damage to your eyes) happen because of the toxic buildup of sugar on cell walls. Catechins can cause the cells to shed extra sugar off their walls [2]. This can prevent complications.  

            When put to the test, green tea appears to have a small but beneficial effect on blood sugar. Research found that people who drink green tea every day had an average blood sugar 10 points lower than those who don’t drink green tea [3].

A different study looked at blood sugar when subjects were given green tea. The researchers took a group of diabetics. They split the diabetics into 2 groups. One group got 1 bag of green tea every day for 90 days and the other group got a placebo. At the end of the study, diabetics drinking green tea saw their blood pressure drop by about 5 points and saw their average fasting blood sugar drop by about 2 points [4].

            A review pooled together results of 17 different studies on green tea and diabetes. They found that on average, those who drank green tea every day had a lower fasting blood sugar of about 2 points and a lower A1C by about 0.3% [5]. While these benefits are small, green tea also has protective effects to prevent complications of diabetes.

Green Tea and Diabetic Complications: Kidney Failure

            Green tea could help protect against kidney disease. Green tea prevents sugar from building up and damaging the kidneys. It can also help reduce inflammation. Studies on diabetic rats showed that kidney function improved when the rats were given green tea [2].

Heart Disease

            Diabetics are at risk for heart disease, but green tea has many protective components. Green tea can help activate metabolic pathways to make nitric oxide, which helps blood vessels dilate. This improves blood flow [2]. It can also reverse hardening of the arteries. Catechins help prevent the body from making too many fatty acids and the build up of fat in the arteries [2]. Drinking green tea also lowers blood pressure [4].

Other Health Problems

            Green tea can help prevent diabetic neuropathy. Remember those free radicals I mentioned earlier? The ones that destroy insulin receptors? They wreak havoc on nerves too. Catechins and other antioxidants help neutralize damaging free radicals [2].

            Diabetic retinopathy is a common problem for diabetics. Green tea can help protect against diabetic retinopathy. Diabetic rats given green tea experienced less inflammation in the eye. They had fewer cellular changes that cause damage to the retina [2]. Another study found that diabetic Chinese women who drank at least 1 cup of green tea a week were less likely to develop diabetic retinopathy [3]. The benefit men saw was smaller (but they still did see a benefit!).

Catechins also bind to different proteins that may cause obesity, metabolic syndrome, diabetes, and cancer. By modifying these proteins, these diseases may be prevented [6]. Green tea has also been shown to help with weight loss, with people losing about 3 pounds on average [1].

How Much Green Tea Should I Drink?

            While even 1 cup can have benefits for blood sugar, 4 cups a day maximizes benefits [1]. An 8-ounce cup of green, caffeinated tea has about 168 mg of catechins. Many of the studies I looked at had subjects drinking 300 to 600 mg of catechins in their green tea beverage [1]. Decaffeinated green tea has less catechins then caffeinated tea [1]. Loose tea leaves don’t have a higher antioxidant content then tea in a bag.  Try to steep your tea for at least 5 minutes to optimize the antioxidant and polyphenol release [7]. Freshly brewed tea has more antioxidants then ready-to-drink teas in bottles and cans. Avoid any teas with added sugars.

Can I Drink Too Much?

            The studies I reviewed did not see any side effects when people drank 4 cups or less a day. Green tea does have some caffeine, so if you drink too much you may get shaky, nervous, jittery, have heart palpitations, or difficulty sleeping. Basically, all the side effects of too much caffeine. Some research has shown that tea can affect iron absorption, but unless you have iron deficiency, you should be fine. People who drink 10+ cups a day may get a stomachache, have gas, dizziness, or muscle pain [1].

While you can have too much of a good thing, most people aren’t drinking 10+ cups of green tea. So, enjoy a freshly brewed cup of green tea today and feel good about helping your diabetes.  

Works Cited

[1] A. Basu, “CPE Monthly: Health Benefits of Tea — Learn About the Effects of Tea on Health, Including Its Role in the Prevention of Many Diseases,” Today’s Dietitian , 2017. [Online]. Available:
[2] J.-M. Meng, S.-Y. Cao, X.-L. Wei, R.-Y. Gan, Y.-F. Wang, S.-X. Cai, X.-Y. Xi, P.-Z. Zhang and H.-B. Li, “Effects and Mechanisms of Tea for the Prevention and Management of Diabetes Mellitus and Diabetic Complications: An Updated Review,” Antioxidants, [Online]. Available:
[3] Q. Ma, D. Chen, H.-P. Sun, N. Yan, Y. Xu and C.-W. Pan, “Regular Chinese Green Tea Consumption Is Protective for Diabetic Retinopathy: A Clinic-Based Case-Control Study,” Journal of Diabetes Research, [Online]. Available:
[4] M. Ali, S. Mudassar, F. Mahmood, M. S. Humza, J. Nawaz, A. Noor, M. N. Fahimul-Haq and U. Nisar, “Effects of Green Tea Consumption on Blood Pressure and Blood Glucose Levels among Type 11 Diabetic and Non Diabetic Individuals,” 2019. [Online]. Available:
[5] K. Liu, B. Wang, K. Chen, L.-Y. Shi and J.-D. Zhu, “Effect of green tea on glucose control and insulin sensitivity: a meta-analysis of 17 randomized controlled trials,” American Journal of Clinical Nutrition, 2013. [Online]. Available:
[6] C. S. Yang, H. Wang and Z. P. Sheridan, “Studies on prevention of obesity, metabolic syndrome, diabetes, cardiovascular diseases and cancer by tea,” Journal of Food and Drug Analysis, 2018. [Online]. Available:
[7] R. Cleverdon, Y. Elhalaby, M. McAlpine, W. Gittings and W. E. Ward, “Total Polyphenol Content and Antioxidant Capacity of Tea Bags: Comparison of Black, Green, Red Rooibos, Chamomile and Peppermint over Different Steep Times,” Beverages, 2018. [Online]. Available:

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