Type 2 diabetes is a chronic condition that affects more than 35 million people in the United States. Close to 100 million Americans have prediabetes, a condition that can lead to type 2 diabetes. In people with type 2 diabetes, the body’s cells don’t respond normally to insulin. This is called insulin resistance. In response, the level of glucose (blood sugar) rises.

Effective management of type 2 diabetes often requires a combination of medication, regular physical activity, changes in diet, weight loss, and blood sugar monitoring. Research has also suggested that drinking green tea may help manage or even head off type 2 diabetes.

Keep reading to learn more about the scientific evidence behind green tea’s potential role in managing type 2 diabetes, its benefits and risks, and how to incorporate it into your diet.

The Science Behind Green Tea and Type 2 Diabetes

Although green tea has been around for thousands of years, Western medicine has only recently begun to recognize and study its potential health benefits for a number of conditions, including type 2 diabetes.

Green tea is made from the leaves of the Camellia sinensis plant. Black tea is derived from the same plant, but green tea goes through a special quick-drying process that brings out its healthy properties.

Green tea leaves contain flavonoids called catechins. These are thought to play a significant role in green tea's potential health benefits due to their antioxidant effects.

“Although the exact mechanism for how green tea may help with type 2 diabetes is an active area of research, it’s likely that catechins improve insulin function,” says Richard Bruno, PhD, RD, a professor of human nutrition at Ohio State University in Columbus who has published research on the effects of green tea and green tea extract. “Some of these benefits potentially occur by improving gut microbiota composition and function, reducing gut inflammation and ‘leaky gut’ to limit the absorption of pro-inflammatory, gut-derived toxins, and decreasing insulin resistance.”

Lab studies have also shown that certain components of green tea extracts, including L-theanine, an amino acid, can help with glucose uptake and possibly improve fasting glucose and A1C, says Marilyn Tan, MD, an associate professor of medicine and endocrinologist at Stanford Health Care in California. More research in humans is needed to back this up, however.

Benefits of Green Tea for People With Type 2 Diabetes

Green tea may help manage type 2 diabetes in a few key areas, including blood sugar, weight, and inflammation.

Blood Sugar Regulation

Green tea may help regulate blood sugar levels by improving insulin sensitivity, allowing the body to use insulin more effectively. Some experts believe that this may help prevent type 2 diabetes.

Researchers in Japan looked at L-theanine levels and green tea consumption and found that green tea drinkers were significantly less likely to develop type 2 diabetes over seven years.

A study of over half a million people in China found that daily green tea drinking was associated with a lower risk of developing type 2 diabetes and a low risk of premature death from any cause in people who already had diabetes.

Dr. Bruno conducted a trial using green tea extract gummies that included 40 people: 21 with metabolic syndrome and 19 healthy adults. Metabolic syndrome includes several conditions that increase the likelihood of developing heart disease, stroke, and type 2 diabetes. All participants consumed green tea gummies for 28 days. The daily dose was equivalent to five cups of green tea. After a one-month break from consuming any green tea products, the participants were given placebo gummies, also for one month. Researchers found that fasting blood glucose levels for all participants were significantly lower after taking the green tea gummies compared with levels after taking the placebo.

Weight Management

Maintaining a healthy weight can help manage type 2 diabetes, though the evidence on green tea and weight loss is mixed.

Some studies have shown that the polyphenols in green tea — antioxidants that may improve metabolism and reduce fat absorption — can promote weight loss, but other research does not support these results.

A study of over 10,000 middle-aged adults found that women who drank at least four cups of green tea a week were less likely to have abdominal obesity than women who didn’t drink it, though the same benefits weren’t found in their male counterparts.

A review of the effects of green tea supplements on obesity found that there could be some modest improvements in weight or waist circumference in people who took the supplements for three months or longer.

The bottom line, says Dr. Tan, is that the effects of green tea on weight control are not proven, and how it could help shed pounds remains unclear.

Cardiovascular Benefits

People with type 2 diabetes are at a higher risk of cardiovascular disease, including heart disease. Some studies suggest that green tea may offer cardiovascular protection by improving levels of LDL (“bad”) cholesterol as well as total cholesterol.

A meta-analysis of five studies totaling over 600,000 people concluded that those who drank two to four cups of green tea a day lowered their risk of stroke between 21 and 24 percent.

One theory is that the flavonoids in green tea open blood vessels and keep them flexible, helping blood flow more freely.

Green tea is also associated with lowering chronic high blood pressure. A meta-analysis of randomized, placebo-controlled trials found that green tea lowered both systolic and diastolic blood pressure.

Anti-Inflammatory Effects

Chronic inflammation is common in people with type 2 diabetes and is believed to play a role in insulin resistance.

Green tea’s effect on inflammation in the body is less clear than the benefits for weight loss and blood sugar, says Bruno.

“However, it should be noted that inflammation is a complex interplay that involves many aspects of the immune system, and it is difficult to generalize effects regarding inflammation because there are many different inflammatory proteins that, when at appropriate levels, support health and well-being, but when dysregulated — either too high or too low — can be harmful to health. That being said, recent evidence indicates that green tea may reduce specific indicators of gut inflammation,” says Bruno.

How to Add Green Tea to Your Diet

Bruno recommends that people with prediabetes and type 2 diabetes drink green tea consistently to maximize the benefits.

“Because catechins are poorly absorbed by the body and rapidly eliminated from the body, it is best to consume green tea or catechins throughout the day,” he says.

How Much Green Tea Do You Need to Drink?

There isn’t a clear consensus on how much green tea is necessary to reap the health benefits, says Bruno.

“It appears that approximately five cups of tea daily is associated with health benefits. Excess tea consumption does not appear to have adverse effects, except among those who may not tolerate caffeine,” he says.

“And remember, green tea isn’t a magic bullet for weight control or blood sugar management,” says Bruno. “It can’t be expected to overcome an otherwise poor diet or inactive lifestyle.”

How to Brew the Perfect Cup of Green Tea

Both decaffeinated and caffeinated green tea contain catechins, although the decaffeination process can reduce the amount of catechins present, says Bruno.

“The type of green tea is not all that important, but the way it is brewed is. Too hot or too cold does not result in brewed tea that is as rich in catechins, whereas an in-between temperature that comes down to about 185 degrees F after boiling water seems to be ideal for brewing tea,” he says.

How long you steep the tea impacts the catechin content of tea as well. “Three minutes appears to be ideal. And catechins readily degrade in water. After about an hour, notable losses of catechins can occur,” says Bruno.

Remember that you can also undo the benefits of green tea by what you put in it.

“Green tea comes in many forms, which may include matcha drinks and boba, also known as bubble tea, and these can contain a significant amount of sugar and fat,” says Tan.

Potential Risks and Side Effects

Green tea naturally contains caffeine, although in lower amounts than coffee. While moderate caffeine consumption is generally safe for most people, excessive intake (more than eight cups per day) can lead to side effects like insomnia, jitteriness, or upset stomach. People sensitive to caffeine should be mindful of their green tea intake or opt for decaffeinated tea.

Green tea may interact with certain medications, including warfarin (a blood thinner), nadolol (a beta-blocker), and statins (medications used to lower cholesterol).

If you’re concerned about how green tea may impact any medications you are taking, talk with your healthcare provider.

Supplements containing catechins have been linked to acute liver toxicity that goes away when the supplements are stopped, says Bruno. “Most recommendations suggest limiting supplements to less than 800 milligrams and to take with food to minimize chances of adverse effects,” he says.

While green tea is generally safe for most people, certain groups should avoid it or limit their intake. Pregnant women, for example, should be cautious with green tea because of its caffeine content, which could affect pregnancy or fetal development. Additionally, individuals with certain health conditions, such as liver disease, may need to limit their consumption.

The Takeaway

Green tea has several potential benefits for people with type 2 diabetes, including improving blood sugar regulation, supporting weight management, and offering cardiovascular and anti-inflammatory benefits.
To maximize these benefits, aim for five cups of green tea per day, but be mindful of caffeine intake and any possible interactions with medications.
Remember that green tea is not a cure for type 2 diabetes. A comprehensive approach that includes regular physical activity, a balanced diet, and proper medical care is essential for managing type 2 diabetes.
Always consult a healthcare provider before making significant dietary changes.

Lynn Grieger, RDN, CDCES

Medical Reviewer

Lynn Grieger is a registered dietitian-nutritionist, certified diabetes care and education specialist, certified personal trainer, and certified health and wellness coach. She completed requirements to become a registered dietitian at Valparaiso University in 1987 and completed a dietetic internship at Ingalls Memorial Hospital in Harvey, Illinois, in 1988.

Lynn brings her expertise in nutrition, exercise, and behavior change to her work in helping people reach their individual health and fitness goals. In addition to writing for Everyday Health, she has also written for websites and publications like Food and Health Communications, Today's Dietitian, iVillage.com, and Rodale Press. She has a passion for healthy, nutrient-dense, great-tasting food and for being outdoors as much as possible — she can often be found running or hiking, and has completed a marathon in every state.

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Becky Upham

Author

Becky Upham has been professionally involved in health and wellness for almost 20 years. She's been a race director, a recruiter for Team in Training for the Leukemia & Lymphoma Society, a salesperson for a major pharmaceutical company, a blogger for Moogfest, a communications manager for Mission Health, a fitness instructor, and a health coach.

She majored in English at the University of North Carolina and has a master's in English writing from Hollins University.

Upham enjoys teaching cycling classes, running, reading fiction, and making playlists.

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Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.

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