The Truth about Green Tea
A Health Powerhouse or Mostly Hype?
-- By Becky Hand, Licensed and Registered Dietitian
Whether you drink it as a hot beverage to ward off Old Man Winter or iced to cool off on a hot summer day, tea is an invigorating drink that people around the world consume in copious amounts. In America alone, each person drinks approximately 155 cups of tea per year! And as researchers discover more health benefits from those little leaves, tea sales continue to climb. But we're not just drinking tea; its extracts are becoming popular supplements and additions to other foods and drinks.
If you drink tea because you enjoy the taste, great. But if you're buying foods or supplements that contain tea extracts, thinking they'll help lower your risk for cancer and heart disease, speed your metabolism, or help you lose weight as many products claim, think again. Let's look at what research (and common sense) really tells us about tea, tea extracts and supplements, and what they can—and can't—do for your health.
First Things First: What is Tea?
Technically, only one plant provides the leaves to make what we know as tea: Camellia sinensis. The difference in the flavor, color, and name of the tea depends on how the leaves are processed. There are four basic types of tea:
Black tea is the most popular variety in the United States. When you drink a regular cup of hot tea, iced tea, or sweet tea, you are drinking black tea. Black tea comes from tea leaves that were exposed to the air and allowed to fully oxidize or ferment, changing the leaves from green to black.
Oolong tea varies in the fermentation time. It therefore falls between black and green tea.
Green tea is less processed and is not fermented like black tea is. These tea leaves therefore retain their green color and delicate flavor.
- White tea is the least processed of all teas. The leaves are picked at a very young stage and are only dried in the sun.
Components of Tea: Catechins and Caffeine
Flavonoids are dietary compounds found in tea and other foods such as wine, cocoa, fruits and vegetables. Flavonoids determine the color and taste of food and may be involved in healthy body functions. The average U.S. adult consumes 189.7 milligrams of flavonoids each day, most of which (157 mg to be exact) come from tea. While there is currently no recommendation for flavonoid consumption, experts are in the initial stages of discussion regarding recommendations for these dietary components. Tea contains approximately 100-300 milligrams of flavonoids per serving, depending on the type of tea. The main type of flavonoids found in tea are catechins. Because the green tea variety is less processed, it contains more catechins than black tea does. Therefore green tea and green tea extracts have received the most research regarding possible health benefits and will be the focus of this particular article. Research has primarily investigated the health benefits of catechins such as epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC).
Green tea also contains 2% to 4% caffeine or about 10-80 milligrams per cup. (For reference, a cup of regular coffee contains 95 mg of caffeine, while 1 oz. of dark chocolate contains 23 mg.) Caffeine has also been the topic of many research studies regarding the health benefits of green tea.
Health Benefits of Green Tea: What the Research Really Shows
The research to date indicates that green tea is likely effective for:
Improving mental alertness. Because of the caffeine content, green tea and other caffeinated beverages can help maintain alertness and cognitive ability when used throughout the day.
- Treating genital warts. An FDA prescription ointment that uses green tea extract heals genital and perianal warts in 24-60% of patients.
Improving cholesterol levels. Green tea may help reduce elevated levels of LDL ("bad") cholesterol, total cholesterol, and triglycerides while increasing HDL ("healthy") cholesterol in the blood. However, more clinical studies are needed in this area.
Preventing low blood pressure upon standing and after eating (in the elderly population). This is likely due to the caffeine content of green tea.
Reducing the risk or preventing the onset of Parkinson's disease.This is also attributed to the caffeine content.
- Preventing cancers of the bladder, esophagus, ovaries and pancreas. Most of these studies have been conducted on animals, but a few involved testing green tea extracts on people. More research is needed.
Weight loss. Some scientists have speculated that caffeine and the catechin EGCG may act together to increase fat oxidation (fat burning). However, the big question remains: Do tea or catechins in tea have any real impact on a person's weight? The evidence for this is pretty thin. In a handful of small studies that only lasted one to three days, people who took EGCG plus caffeine burned slightly more calories than those who were given a placebo. In longer-term studies, the administration of EGCG did bring about a slight reduction in body weight, body mass index, and waist circumference. However, the reductions were modest at best and did not benefit weight maintenance in the long run. The bottom line: Green tea is no magic pill for weight loss. Currently, there is not enough sound research to suggest that green tea, green tea extracts, or green tea supplements help people lose weight.
Type 2 diabetes prevention. Japanese adults who self-reported drinking 6 cups of green tea or more had a lower incidence of type 2 diabetes in one small study. However, this is not enough to say that green tea definitely prevents type 2 diabetes in everyone else because this was just one small epidemiological study.
Prostate cancer prevention. Prostate cancer risk was lower in Chinese men who drank more green tea, according to one study. However, other clinical studies suggests that higher green tea consumption does not have any effect on prostate cancer or Prostate-Specific Antigen (PSA) levels. More research is needed before applying either of these results across the board.
Breast cancer prevention. Most research on green tea for breast cancer has been in Asian populations. According to the available research, green tea does not appear to prevent breast cancer in Asian populations. The effect of green tea on breast cancer risk in Western populations is less clear. However, within Asian-American populations, some studies indicate that green tea consumption may reduce the risk of breast cancer. There is conflicting evidence on this topic and more research is needed.
Lung cancer prevention. Currently, the results of studies on green tea and lung cancer risk are conflicting. A large-scale study in Japan indicated no significant reduction in lung cancer risk associated with green tea consumption. However, smaller, less significant epidemiological research suggests that men who consumed a higher amount of green tea had a 27% lower risk of developing lung cancer.
- Gingivitis. A single study indicated that chewing gum that contains green tea extract may help control plaque build-up and swelling of the gums.
How to Get the Health Benefits of Green Tea
While green tea is rich in antioxidants, studies have shown that the bottled varieties of tea don't even come close to the antioxidant levels you'll find in home-brewed green tea. Researchers found as few as 3 milligrams of flavonoids in premade (bottled) teas, compared with up to 150 milligrams in the kind that is brewed at home. To get the most of your tea, steep it at home for 6-10 minutes, then enjoy it either hot or iced. (This will save you money, too!)
It should be noted that green tea extracts and green tea supplements have not been as widely studied as the fresh-brewed beverage itself has been. Most research on the health benefits of tea applies to tea drinking alone. Whether any of these benefits can be achieved by taking a pill or extract, drinking an energy drink with EGCG added, or eating a packaged food product that contains extracts of green tea is questionable. Many of these products contain so little green tea that they'd offer no benefit at all. Others may contain high levels that can be unhealthy (see warnings below). Your best bet is to stick with a fresh-brewed cup of tea and not spend extra on costly functional foods or supplements.
Warnings with Green Tea and Green Tea Extracts
Beverage experts suggest no more than 5 cups (40 ounces) of tea daily for a healthy adult, for a maximum intake of no more than 400 milligrams of caffeine daily. While green tea is likely safe for most adults in moderate amounts, too much green tea can bring about side effects due to the caffeine content. Side effects can vary from mild to moderate headache, nervousness, sleep problems, vomiting, diarrhea, irritability, irregular heartbeat, and dizziness. Excessive consumption of tea can also bring on stomach upset or constipation. And believe it or not, extremely high doses of green tea can be fatal! Here are a few additional cautions of which to be aware.
During pregnancy, green tea is safe in small amounts—no more than 2 cups daily, which provides about 200 milligrams of caffeine. Caffeine intakes higher than this have been linked to miscarriage and other harmful effects.
Green tea can also decrease the absorption of iron and folic acid. Therefore it is best to be drink tea between meals rather than using it as your mealtime beverage. Wait 1-2 hours between eating foods rich in iron and folic acid and drinking tea to maximize your absorption of these nutrients.
Caffeine does pass into a woman's breast milk and can affect a nursing infant. Moderation is the key for nursing mothers; no more than 2 cups daily is advised for the breastfeeding mom.
Green tea and green tea extract can interact with numerous medications. Therefore, you should always discuss your green tea beverage consumption and use of green tea supplements with your physician or pharmacist prior to usage.
- People with any medical condition should discuss the intake of green tea or green tea extract with one's physician prior to usage.
Brew Up a Cup
Taken all together, there does appear to be some health benefits in that little cup of green tea. A few cups a day could have a positive effect on your health. It's probably not going to cure any disease, and should not be consumed as a drug; but as part of your overall healthy diet, drink up!
Degradation of Green Tea Catechins in Tea Drinks, from Journal of Agriculture and Food Chemistry
Effect of Green Tea Catechins with or without Caffeine on Anthropometric Measures: A Systematic review and Meta-Analysis, from American Journal of Clinical Nutrition
Estimated Dietary Flavonoid Intake and Major Food Sources of U.S. Adults, from The Journal of Nutrition
Green Tea, from Natural Medicines Comprehensive Database