Dr. Louise Achey
Q: Can green tea help lower my blood sugar? I was diagnosed with diabetes last month. My sister recommended drinking green tea.
Green tea contains antioxidants. Drinking at least 3-5 cups of green tea daily has been shown to reduce the risk of cardiovascular disease, endometrial cancer, and ovarian cancer. It also may lower blood pressure, blood sugar, body weight, and body fat. What is confusing is that green tea and green tea extract also naturally contain caffeine, increasing blood pressure and heart rate in people who are sensitive to it.
Green tea contains caffeine plus another natural compound called epigallocatechin gallate (EGCG). Amounts of EGCG over 200mg daily have been associated with increased blood pressure, constipation, and rash. Higher concentrations of 800mg daily of EGCG have been associated with liver injury.
High amounts of green tea can cause depletion of folic acid from the body. Folic acid is critical in preventing a severe birth defect called spina bifida.
Green tea extracts verified with the United States Pharmacopeia (USP) must warn consumers about the potential for liver toxicity. Their labeling has to include the following statements: “Do not take on an empty stomach. Take with food. Do not use if you have a liver problem and discontinue use and consult a healthcare practitioner if you develop symptoms of liver trouble, such as abdominal pain, dark urine, or jaundice (yellowing of the skin or eyes).”
Most tea leaves are harvested from the woody plant Camellia sinensis, then carefully dried to prevent mold. Herbal teas use various parts of other plants, like chamomile and peppermint. About 20% of the teas from the leaves of Camellia sinensis are green teas.
The main difference between green and black teas is the amount of oxidation they undergo after harvesting. When the tea leaves are exposed to the air, oxidation occurs, turning them from bright green to brown, similar to an apple turning brown after cutting and exposing it to air.
Green tea is steamed or pan-fried right after harvesting to arrest the oxidation process before being dried. Black teas are left exposed until the oxidation process is completed, then dried and packaged. Oxidation makes tea leaves less bitter and helps develop their flavors more fully than green or white teas.
Oolong teas are the middle ground between barely oxidized green tea and fully oxidized black tea. Oolong teas can be anywhere from 5% to 90% oxidized. The less oxidation, the lighter the color of the leaves and the more subtle their flavor.
All teas from Camellia sinensis contain caffeine, about 50mg per cup. This compares with 90-100mg of caffeine in a cup of coffee. When green tea is concentrated in an extract, it retains its caffeine content. The label on green tea extract and supplements containing it won’t state the total amount of caffeine present because green tea naturally contains caffeine.
Besides coffee and tea, there are two other plants cultivated, processed, and brewed for the stimulant effects of the caffeine they contain. Guarana and Yerba Mate contain caffeine naturally and are often added to supplements for weight control and increased energy.
Supplements have to state on their label any caffeine that has been added to their product. Like green tea, guarana and Yerba Mate also naturally contain caffeine, so their caffeine doesn’t have to be listed separately as an ingredient.
5 Ways to Get the Most From Green Tea
1. Beware of the TOTAL Caffeine Content.
Caffeine lurks in natural compounds like green tea, guarana, and yerba mate. Herbal supplements must list any caffeine that has been added to their product. Caffeine in green tea can cause stomach upset, insomnia, and a racing heartbeat.
2. Brew at a Lower Temperature.
Black and oolong teas are best steeped in boiling water, but green and white teas taste bitter and grassy if brewed in water that’s too hot. Brew green tea with water heated until tiny bubbles rise to the surface of your pan or glass kettle, about 175-180 degrees.
3. More is Not Always Better.
One compound found in green tea extract is EGCG, which at high doses can damage your liver.
4. Avoid it if You Are Trying to Get Pregnant.
High doses of green tea or green tea extract deplete your body of folic acid, increasing the risk of severe birth defects like spina bifida.
5. Drink 3-5 cups Daily for Best Results.
Most studies show that drinking 3-5 cups daily of green tea, or the equivalent in green tea extract, was necessary to experience the benefits.
Dr. Louise Achey, Doctor of Pharmacy, is a 42-year veteran of pharmacology and author of Why Dogs Can’t Eat Chocolate: How Medicines Work and How YOU Can Take Them Safely. Get clear answers to your medication questions at her website and blog TheMedicationInsider.com.®2021 Louise Achey
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