…for guarding against heart disease, cancer and more

Prevent cancer… fight heart disease… lose weight… avoid cavities… improve your digestion… and more. Green tea is purported to have such a wide variety of health benefits that it makes many people wonder whether its salutary effects are being oversold.

To learn the truth, Bottom Line/Health spoke with Lester A. Mitscher, PhD, a professor of medicinal chemistry and leading expert on green tea.

TEA-DRINKING TRADITION

Tea, which is widely recognized as a rich source of healthful antioxidants called catechins, is the most consumed beverage in the world (aside from water).

All tea is produced from leaves of the Camellia sinensis plant, which are picked, rolled, dried and heated.* For black tea, the leaves are fermented and oxidized.

Green tea is less processed, which may explain why it is an even richer source of antioxidants than black tea. (White tea, made from the youngest tea leaves, contains slightly more antioxidants than green tea but is not as widely available and is much more expensive.)

What you may not know: To ensure that more than 80% of the catechins in your tea are released, steep the leaves for five minutes. A squeeze of lemon also seems to preserve tea’s catechin levels. Don’t reuse tea bags — most of the catechins are released in the first cup. Instant tea provides insignificant levels of catechins.

WHY GREEN TEA?

The average person in China or Japan drinks up to four cups of green tea a day. Because these countries traditionally have had relatively low rates of heart disease, cancer and other chronic ailments, researchers began wondering years ago whether green tea may play a role.

Since then, hundreds of studies have been conducted in the US and elsewhere. The majority of these studies show a strong link (based on epidemiological studies) between green tea consumption and various health benefits.

There are some scientists who believe that the evidence is not yet conclusive, but there is widespread agreement that green tea’s polyphenols (a class of substances that include catechins) are among the most potent antioxidants ever discovered.

Important: Three eight-ounce cups of green tea daily is the minimum amount found to be helpful in most studies. Green tea supplements (300 mg to 400 mg daily) generally confer the same benefits as brewed green tea.

Caution: Green tea is safe for most people, but it’s wise to consult your doctor before regularly drinking three or more cups a day or taking green tea supplements. In both forms, green tea can interact with certain medications, including blood thinners, some antibiotics and anti­psychotic drugs.

Green tea also contains caffeine (about 30 mg per cup). Green tea supplements contain caffeine in varying amounts, depending on how they are prepared. Decaffeinated green tea (2 mg of caffeine per cup) contains lower levels of polyphenols, as do decaffeinated green tea supplements.

Latest research findings…

CANCER

The catechins in green tea have been shown in animal studies to inhibit cancer growth. Human studies also have yielded promising results.

Scientific evidence: In a study of 18,000 Chinese men, tea drinkers (mostly green tea) were about half as likely to develop stomach or esophageal cancer as men who drank little tea. Other research conducted in Asia has linked green tea consumption to reduced risk for bladder, colon, prostate, breast and pancreatic cancers.

Researchers speculate that substances in green tea increase levels of antioxidant enzymes that protect DNA from carcinogenic changes. Green tea also contains epigallocatechin gallate (EGCG), a primary class of polyphenols. EGCG is thought to inhibit the growth of blood vessels that tumors need to grow and spread.

My advice: Drink green tea one hour before a meal — the food you eat can interact with green tea’s components and reduce their antioxidant power.

Caution: If you have cancer, be sure to check with your oncologist before drinking green tea or using green tea supplements — there are no long-term studies that show the effect of either on cancer treatments.

DIGESTION

Green tea enhances the proliferation of beneficial probiotic organisms in the intestine. People with adequate amounts of these organisms typically have less constipation and other digestive complaints.

Scientific evidence: At the start of one study of 37 volunteers, only half reported that they had regular bowel movements. After 12 weeks of taking green tea catechin capsules, that number increased to 80%.

HEART HEALTH

A growing body of evidence suggests that green tea may help protect against cardiovascular disease — including research that shows it reduces stroke risk by 21%.

Scientific evidence: When researchers combined data from 17 prior studies, they found that people who drank three cups of green tea daily decreased the risk for a heart attack by 11%.

Researchers theorize that these benefits are due to green tea’s ability to lower cholesterol (which can accumulate on artery walls) and reduce blood clots.

ORAL HEALTH

To improve their oral health, people in China and Japan often swish (and spit out) a little green tea after meals. Both animal and human studies support this practice.

Scientific evidence: In one study, 35 volunteers abstained from brushing or flossing — their only oral hygiene involved rinsing their mouths with a polyphenol solution. Their levels of plaque were significantly reduced even in the absence of flossing and brushing.

WEIGHT LOSS

Green tea increases thermogenesis, the expenditure of energy (calories) during metabolism. People who drink tea or take green tea supplements can have a 3% to 4% increase in metabolism. This won’t cause dramatic weight loss, but it can make a difference over time.

Scientific evidence: A study of moderately obese individuals found that those who took green tea supplements for three months had reductions in body weight of 4.6%, on average, and nearly a 5% decrease in waist circumference.

HOW TO BECOME A GREEN TEA LOVER

About 50 types of Chinese or Japanese green tea can be found at specialty-food stores or online.

If you don’t like the taste of green tea, add lemon and/or one teaspoon of sugar or honey — and try iced green tea.

To prepare: Place one bag of green tea for every cup of very hot water in a glass pitcher, allow to cool, then refrigerate. Add sweetener (described above), if desired. To enhance the tea’s flavor and promote digestive health, add fresh ginger root.

*So-called herbal teas are produced from various herbs steeped in hot water.