Green Tea and Diabetes
Blood Sugar and Insulin Sensitivity

Five green tea and diabetes studies show how tea may regulate blood sugar levels and improve insulin action.

When you have diabetes, your body is not very good at converting blood sugar into energy. This can happen in two ways:

  • The body does not make enough insulin, a hormone that causes glucose to enter the body’s cells to be converted into energy or fat.

  • The body cells do not respond properly to insulin i.e. low insulin sensitivity.

Often, both mechanisms do not work properly. Without treatment, diabetics can build up high glucose levels in many parts of the body, causing damage to eyes, kidney, nerves and blood vessels.

Increasingly, scientific studies are showing that drinking green tea or consuming tea extract can help by

  • Blocking glucose absorption

  • Improving insulin actions

  • Regulating blood sugar levels

Green Tea and Diabetes Benefit #1:
Block Glucose Absorption

A 2008 study conducted by the University of Massachusetts Amherst investigated the effects of tea and wine had on people with type 2 diabetes.

The researchers discovered that these beverages inhibit an enzyme called alpha-glucosidase, which causes glucose to be absorbed more slowly from the small intestine into the body.

"Levels of blood sugar, or blood glucose, rise sharply in patients with type 2 diabetes immediately following a meal," says Shetty, one of the food scientists who published the research.

"Red wine and tea contain natural antioxidants that may slow the passage of glucose through the small intestine and eventually into the bloodstream and prevent this spike, which is an important step in managing this disease."

Red and white wines, black, oolong, white and green teas were all tested. Red wine was found to be 5 times more effective than white wine. Black tea was the most effective, followed by white tea and oolong tea.

Researchers also conclude that polyphenols in wine and tea could also help in protecting your body from high blood pressure and heart disease, which also pose particular risk to diabetics.

Tea and Diabetes - Antioxidants Reduce Blood Sugar Level

Green Tea and Diabetes Benefit #2:
Improve Insulin Action

A 2002 study conducted by the BHNRC found that brewed tea raised insulin activity by more than 15 times when it was added to the fat cells of laboratory rats.

The animals were divided into three groups and over the course of 12 weeks and given either

  • Water,

  • A high fructose diet and water, or

  • The same high fructose diet but with green tea (0.5 gram of lyophilized green tea powder) instead of water

The group given fructose developed hyperglycaemia, hyperinsulinemia, and elevated blood pressure. The green tea group showed improvement in all of these metabolic defects, and in insulin resistance and maintenance of normal blood pressure.

Green Tea and Insulin - 15 Time More Effective

Green Tea and Diabetes Benefit #3:
Promote Glucose Metabolism

A 2004 study jointly conducted by Japan and Taiwanese researchers concluded green tea is anti-diabetic in human and mice.

22 healthy adults participated in the study. They drank either green tea (made from 1.5 gram of powder) or hot water. Blood glucose levels were measured before and 30, 60, and 120 min after drinking the beverages.

After 120 minutes, those who drank green tea had a blood glucose level of 120 mg/dl versus 100 mg/dl for those drank water.

The other part of the study found that green tea tended to lower blood glucose levels (BGL) at 150 mg/kg, and significantly lowered BGL at 300 mg/kg.

Green Tea and Diabetes Benefit #4:
Reduce Blood Sugar Level

The HNRCA's Lipid Metabolism Laboratory, led by Ernst Schaefer, recently completed a pilot study using 8 volunteers with type II diabetes. Their blood sugar levels dropped by 15 to 20 percent after drinking 6 cups of tea per day for 8 weeks.

A new 24-week, randomized, double-blind study involving 40 male and female volunteers with type II diabetes has been launched to follow up on these findings.

Green tea in addition to a low fat Asian diet may be your best bet for keeping blood sugar low.

A study conducted on rats compared the effects of a Western diet, a vegetarian diet and a Japanese diet, each with or without green tea. The researchers concluded that Japanese eating habits combined with drinking green tea is the best for preventing type 2 diabetes.

Green Tea and Blood Sugar


As tea contains caffeine, anyone suffering from diabetes should consult with their doctor before starting a tea program. This exciting research, however, indicates that drinking green tea can be a safe and effective way to regulate glucose level.

Further research will be needed to understand exactly how tea regulates blood sugar and what doses are optimal. So please come and visit often!


News Release: Antioxidants in Red Wine and Tea May Help Regulate Blood Sugar in Type 2 Diabetics, Say UMass Amherst Food Scientists.

Anderson RA, Polansky MM (2002). Tea enhances insulin activity . J Agric Food Chem 50:7182-7186.

Hiroshi Tsuneki, Mitsuyo Ishizuka,, Miki Terasawa, Jin-Bin Wu, Toshiyasu Sasaoka and Ikuko Kimura (2004). Effect of green tea on blood glucose levels and serum proteomic patterns in diabetic (db/db) mice and on glucose metabolism in healthy humans. BMC Pharmacology 2004, 4:18.

For further information about diabetes, check out Erich's website

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