Tea for Health

This summer, don't hesitate to cool off with a glass of (unsweetened) iced tea. A new study emphasized the many health benefits of the second most popular beverage in the world.

Green tea, black tea and oolong tea are all infusions of dried leaves from the Camellia sinensis plant. Researchers from Wayne State University in Detroit, MI, explained that tea leaves contain polyphenolic compounds known as catechins. These molecules function as powerful antioxidants and may improve health and reduce the risk of disease.

The researchers observed that although tea has been consumed for centuries, it has only recently been studied extensively as a health-promoting beverage that may act to prevent a number of chronic diseases and cancers.

Green tea consumption is associated with lower plasma concentrations of cholesterol. Thus, green tea may be of modest benefit in preventing atherosclerosis or the hardening of the arteries. Furthermore, the cancer-preventive effects of green tea are widely supported by epidemiological and clinical studies.

In cell culture studies, green tea catechins induce cell death and cell cycle arrest in cancer cells, but not in normal cells. In animal studies, green tea can inhibit tumors in various organs such as the skin, lungs, liver, stomach, mammary glands and colon.

Recently, clinical trials have explored the anticancer effects of green tea in humans. Tea is a source of caffeine, a molecule that stimulates the central nervous system and the heart. Caffeine also acts on the kidney as a diuretic increasing urine flow.

One cup of tea contains approximately 50 milligrams of caffeine, depending on the strength of the tea and the size of the cup. Tea also contains polyphenols (catechins, anthocyanins, phenolic acids), tannin, trace elements and vitamins.

The study authors concluded that identifying the molecular targets of green tea polyphenols may pave the way for more well-designed clinical trials. By examining how components of tea interact with various biomarkers of cancer, scientists hope to better understand the mechanisms underlying green tea's anti-cancer activity.

For more information on green or black tea, please visit Natural Standard's Foods, Herbs & Supplements database.

 

Comments

[Kim]

Historically, tea has been served as a part of various ceremonies and has been used to stay alert during long meditations. A legend in India describes the story of Prince Siddhartha Gautama, the founder of Buddhism, who tore off his eyelids in frustration at his inability to stay awake during meditation while traveling through China. A tea plant is said to have sprouted from the spot where his eyelids fell, providing him with the ability to stay awake, meditate and reach enlightenment. Turkish traders reportedly introduced tea to Western cultures in the 6th Century.

[Melissa]

I personally drink green tea for its antioxidant effects. Antioxidants help protect the body's cells from the damaging effects of molecules called free radicals. Free radicals are produced when the body fights against infections. Although free radicals are needed for the body to produce energy, maintain immunity, transmit nerve signals, produce hormones and contract muscles, they may also contribute to the process of aging. A diet rich in antioxidants has been suggested as a possible anti-aging treatment.

[Michael]

Several studies have explored a possible association between regular consumption of black tea and the risk of cancer. This research has yielded conflicting results, with some studies suggesting benefits and others reporting no effects. Laboratory and animal studies report that components of tea, such as polyphenols, have antioxidant properties and effects against tumors. However, effects in humans remain unclear, and these components may be more common in green tea than in black tea.

Some animal and laboratory research suggests that components of black tea may be carcinogenic, although effects in humans are not clear. Overall, the relationship of black tea consumption and human cancer remains undetermined.

[mo]

It’s sort of reassuring to know that good old Lipton black tea (orange pekoe?) may have health benefits. I recently learned that it has been studied for the treatment of many health conditions from asthma to mouth cancer. While the jury is still out, studies like this one will likely spur researchers to pursue high-quality trials for these conditions to clarify the relationship between tea and health. I would be curious about two things: 1) How does one differentiate between the effects of caffeine in tea and other components? 2) Does adding anything to tea (milk, lemon, or honey, for example) have an effect on health? I remember a study that found that women on the west coast had improved bone density that was attributed to the milk in their lattes!

[Jess]

Mo - It's interesting you asked that question because some evidence has suggested that adding milk to tea actually negates the cardiovascular benefits of catechins (which are polyphenols). This effect is thought to occur because of the caseins found in milk. You might want to check out Brown et al.'s paper called "AN INVESTIGATION OF THE INTERACTIONS BETWEEN MILK PROTEINS AND TEA POLYPHENOLS," which was published in 1963, for an overview.

[Leah Cohen]

Good distinction - the effects dairy has on black tea and green tea is definitely an area of interest to researchers. In addition to adding milk to tea, the effect of infusion time is also important for extraction of polyphenols. There are several recent studies that have investigated both of these areas, notably: "Effects of infusion time and addition of milk on content and absorption of polyphenols from black tea." (Kyle, 2007); "Addition of milk prevents vascular protective effects of tea." (Pfeuffer, 2007); and "The effect of milk protein on the bioavailability of cocoa polyphenols" (Keogh,2007).

Another area that is of interest is the effect of soy milk on availability and absorption of polyphenols from black or green tea.

[mo]

I was interested to learn that tea has been studied for its potential effects on asthma. I remember reading in one of those home-remedy books that used to be sold on TV that a natural remedy for an asthma attack was a “steaming cup of coffee.” Research has shown caffeine to improve airflow to the lungs (bronchodilation), but it’s unclear whether the causative agent is the tea or the caffeine.

[mo]

As a Starbucks addict, I did a little research into my “coffee theory.” What I found is that it is likely the caffeine that has the intended beneficial effect. A recent study at Harvard School of Public Health found that caffeine intake was inversely related to breast cancer among post-menopausal women, meaning as caffeine intake goes up, breast cancers go down. Who would have thought that daily latte could be considered a health food?

[Leah Cohen]

I am not so sure if caffeine is beneficial for any condition or for overall health. It's especially important to consider the stress-induced response of caffeine and effects on cortisol and blood sugar levels. Glycosylation of proteins in patients with high blood sugar/diabetes has been linked to a variety of disorders, so caffeine's potentially harmful effects should not be overlooked.

[Helen]

Green tea has been touted as very good for our health, and so I began drinking it a couple of times a day. The only problem is that I didn’t know I was dealing with early stages of reflux, and all caffeine products, including green tea, are a definite no-no with that condition! I’m disappointed, but as soon as I heal the reflux, I intend to get back to drinking the tea.