Steeped in Science — The Potential Health Benefits of Tea
By Marie Spano, MS, RD
Today’s Dietitian
Vol. 8 No. 4 P. 30

Steeped or chilled, tea is hot and under investigation for its functional properties. So far, research is brewing mostly positive results.

Tea has been a popular beverage since ancient times, and through the years there has been much folklore surrounding its purported benefits. Once hailed as an aid to the liver and a body purifier, scientists now know that this popular beverage really does have a variety of health benefits associated with it. Loaded with antioxidant polyphenols (which include flavonoids), naturally calorie free, and available in several varieties, it’s no wonder tea is second only to water as the most consumed beverage in the world.

In addition, tea consumption has been associated with a decrease in several chronic diseases related to free radical-induced damage such as heart disease and some cancers. Also, consumption has been linked to a potential future treatment for Alzheimer’s disease, boosting the immune system, and possibly killing leukemia cells.1-4 Drinking tea has also been associated with improved cognitive and immune function, good oral and bone health, and a reduced risk of kidney stones, osteoporosis, and obesity.5-10 Though we can’t consider it a “body purifier,” this brewed beverage is a great addition to any healthy diet.

Most research to date has examined the health benefits of black and green tea. Research on white tea is still in the early stages, though it has been consumed for more than 1,000 years. Early studies show promising antiviral/antibacterial properties, protection against skin cell damage, and colon cancer. Furthermore, it is widely assumed that all health benefits of green tea apply to white tea as well. Oolong tea also has several health benefits associated with it, though the research on oolong tea and cardiovascular disease (CVD) is lagging behind that of green and black tea. Herbal tea isn’t really tea but instead a blend of leaves, flowers, and roots from various plants. Though herbal teas may contain some health benefits, they will not be covered in this article.

There are several types of tea to choose from (see sidebar on page 33) and various ways to drink it. Tea bags are probably the most popular, though tea connoisseurs prefer loose leaf. Even tea bags come in two types: “full-leaf” or “dust” (fine tea particles that are not top grade but brew more rapidly).

Cardiovascular Health
Tea’s host of antioxidant-rich polyphenols includes catechin, epicatechin, epicatechin gallate, epigallocatechin gallate (EGCG), and proanthocyanidins. Antioxidants help neutralize free radical damage, which scientists believe damage genetic material and lipids, thereby contributing to many chronic diseases. According to the scientific research firm Exponent, tea provides 87% of the dietary flavonoids consumed in the U.S. diet (information from the national nutrition monitoring surveys that are representative of the U.S. population). Research on flavonoids is increasing rapidly, with scientists finding additional health benefits associated with these compounds and evidence that they work via multifunctional mechanisms to improve markers for cardiovascular health.

Most research on tea and cardiovascular health has focused on blood vessel and endothelial functioning (the ability of blood vessels to dilate to allow for proper blood flow), serum cholesterol levels, and low-density lipoprotein (LDL) oxidation. Each of these factors impacts the risk of myocardial infarction (MI), stroke, and CVD.
Some research indicates that:

• tea drinkers have lower blood pressure;11

• tea may lower cholesterol;12

• black tea may lower LDL cholesterol;13

• short- and long-term consumption of black tea by subjects with coronary artery disease may improve endothelial and blood vessel functioning; and

• tea flavonoids protect LDL from oxidation, thereby inhibiting the formation of atherosclerotic plaques, plasma lipid peroxidation, platelet aggregation, and thromboxane—all factors important for maintaining a healthy circulatory system.14

Epidemiological Research
Epidemiological research supports an inverse association between the risk of stroke and MI and tea consumption.15 While most studies found this relationship when consuming three or more cups of black tea daily, after examining 340 men and women with history of MI compared with age, sex, and community matched controls, a Harvard study found a 44% reduction in heart disease risk in those who drank at least one cup of black tea daily.16

Another epidemiology study found a strong relationship with greater daily tea consumption. The Saudi Coronary Artery Disease Study, which examined 3,430 men and women aged 30 to 70, found 6.3% with indication of coronary heart disease (CHD). After adjusting for other CHD risk factors, they found that those who drank more than six cups of tea per day had a significantly lower prevalence of CHD than non-tea drinkers (p < 0.001). In addition to a positive dose-response effect between tea consumption and lowered CHD risk, six or more cups of black tea daily was associated with lower serum cholesterol and triglyceride concentrations.17

Dutch researchers found that drinking one to two cups of black tea daily resulted in a 46% decrease in severe aortic atherosclerosis. Those who drank more than four cups of tea per day had a 69% lower risk.18

Other epidemiology studies show a significant reduction in fatal and nonfatal first MI and mortality from stroke with increased tea flavonoid intake, as well as decreased risk from stroke with high intake of tea flavonoids.19,20

With tea consumption inversely related to MI risk and mortality, can it benefit those who are already afflicted with CVD? Scientists set out to find the answer to this question by examining a prospective cohort of 1,900 individuals selected from the Determinants of Myocardial Infarction Onset Study. All patients were hospitalized with an acute MI between 1989 and 1994. Sixteen percent (313) of the patients died during a mean follow-up period of 3.8 years post-MI. Trained interviewers assessed self-reported frequency of caffeinated tea consumption over the previous year. Approximately 75% of these deaths were attributed to cardiovascular causes. After adjusting for age and sex, they found an inverse relationship between tea consumption and cardiovascular mortality.21

In Vivo and In Vitro Research
Though epidemiological evidence is very promising, human and animal research on the effect of polyphenols on disease prevention is less clear.22 In a randomized crossover design, 66 patients with coronary artery disease consumed 900 milliliters of either black tea or water daily for four weeks. Endothelial function was measured by examining vasomotor function of the brachial artery with vascular ultrasound at baseline and after each intervention. Of the 50 patients completing the study, results showed that both short- and long-term tea consumption improved endothelium-dependent flow-mediated dilation of the brachial artery and water had no effect (p < 0.001), indicating that black tea may help improve CVD by improving endothelial functioning.23

What about other CVD risk factors? In a small study conducted by the USDA, 15 hypercholesterolemic adults followed a “Step I”-type diet moderately low in fat and cholesterol per the American Heart Association and the National Cholesterol Education Program. In a blinded, randomized, crossover design, subjects were given five servings of black tea per day or a placebo with caffeine or placebo without caffeine (both placebos were matched to tea by color and taste) for three weeks. Compared with the placebo with added caffeine, tea reduced total cholesterol 6.5%, LDL cholesterol 11.1%, apolipoprotein B 5%, and lipoprotein(a) 16.4%. Compared with placebo without added caffeine, tea reduced total cholesterol by 3.8% and LDL by 7.5%, whereas apolipoprotein B, Lp(a), high-density lipoprotein cholesterol, apolipoprotein A-I, and triglycerides were unchanged. Consequently, tea consumption may reduce total and LDL cholesterol significantly, thereby decreasing CHD risk, and this reduction is independent of the caffeine found in tea.24

Other in vitro research shows that green tea polyphenols inhibit the proliferation of aortic smooth muscle cells to prevent the development of atherosclerosis; prevent LDLs from oxidation; and inhibit plasma lipid peroxidation, platelet aggregation, and thromboxane formation—all factors important for maintaining a healthy circulatory system.25-27 Though in vitro and animal studies are promising, human studies on the effect of tea consumption on LDL oxidation are inconclusive.

Cancer
Epidemiology studies show a relationship between tea drinkers and lower rates of several types of cancer. In addition, preliminary in vitro research suggests that tea flavonoids may lower the risk of certain cancers by inhibiting the oxidative changes in DNA from free radicals and some carcinogens.28 Tea may also promote programmed cell death, or apoptosis, and inhibit the rate of cell division, thereby decreasing the growth of abnormal cells.28,29

Rectal Cancer
A study conducted by University of North Carolina researchers found consumption of the equivalent of 2.5 cups of tea per day or more was associated with a 60% drop in rectal cancer risk among Russian women from Moscow as compared with women who drank relatively less than 1.2 cups of tea per day. Those women who drank approximately 1.2 to 2.5 cups of tea per day had a 52% reduction in the risk of rectal cancer.30 In a 12-year study of more than 34,000 healthy women who are postmenopausal and aged 55 to 69, those consuming high levels of catechins experienced up to a 45% decrease in the incidence of rectal cancer. Catechins are a class of flavonoids found in tea, fruits, and vegetables; those derived from tea were most strongly linked to a decrease in rectal cancer.31

Skin Cancer
In a population-based, case-control study evaluating the relationship between citrus peel use and black tea intake and squamous cell carcinoma (SCC) of the skin, University of Arizona researchers found subjects who reported consumption of both hot black tea and citrus peel had a significant decreased risk of skin SCC.32 Another study by the same group of researchers found that tea concentration (strength), brewing time, and temperature all influenced the potential protective effects of hot black tea on SCC.33

Experiments in mice show that administration of green tea, black tea, or specific flavonoids in tea inhibited the growth of established nonmalignant and malignant skin tumors in tumor-bearing mice. In addition, oral administration of black tea inhibited DNA synthesis and enhanced cell death (apoptosis) in both nonmalignant and malignant tumors in tumor-bearing mice.34 The link between tea and skin cancer is not limited to consumption of tea. Studies show that green tea, when applied topically, may protect skin from ultraviolet radiation-induced damage.35,36

Other Cancers
Based on data from the National Health and Nutrition Examination Survey I Followup study, researchers found that tea drinkers had a roughly 42% reduced risk of colon cancer compared with non-tea drinkers. Men who drank more than 1.5 cups of tea per day were found to have a 70% lower colon cancer risk.37 An in vitro animal model showed that black tea polyphenols prevented induced DNA damage to colon mucosa, whereas an in vitro human model showed that EGCG and theaflavins exhibit apoptosis-inducing activity for human colon cancer cell lines.38,39

Studies have also shown the potential for tea to help reduce the risk of digestive, urinary tract, ovarian, and gastric cancer and possibly increase oral cancer cell death.40-44

Other Potential Health Benefits
In addition to showing health benefits associated with CVD and cancer, tea may also be beneficial for cognitive and immune function, oral health, reduced risk of kidney stones, osteoporosis, and obesity.45-48

A recent study published in The American Journal of Clinical Nutrition found that older individuals who drank green tea exhibited better cognitive functioning than those who did not. Researchers examined cross-sectional data on 1,003 70-year-old Japanese subjects.

Each completed a self-administered questionnaire that included questions about the frequency of green, oolong, and black tea consumption, as well as other beverages. Cognitive functioning was measured using the Mini-Mental State Examination. After adjusting for other factors that may affect cognitive functioning such as diabetes, smoking, advanced age, physical activity, social ties, consumption of fish and vegetables, and self-reported overall health, higher green tea consumption was associated with a lower prevalence of cognitive impairment. Those who drank at least two cups of green tea daily exhibited the lowest risk of cognitive impairment.

Coffee and black and oolong tea did not show the same results. Study authors concluded that the results may be due to a few factors. For one, a component of green tea, EGCG, has shown promise in experiments on brain diseases in animals. In addition, people in Japan often socialize over green tea, which may be good for the brain.49

In addition to potentially helping bolster cognitive functioning, tea may also strengthen the immune system. Researchers from Brigham and Women’s Hospital and Harvard University found that tea contains L-theanine, a substance that helps the immune system fight infection, bacteria, viruses, and fungi. In an in vitro clinical trial examining the effect of black tea consumption on immune function, immune cells of participants who drank five cups of black tea daily for two to four weeks secreted up to four times more interferon, an immune defense substance that prevents viral replication, suggesting that black tea may bolster the immune system’s response to microbial infection.50

A few studies that have examined the role of tea in oral health have shown that tea may inhibit plaque formation and the fluoride in tea may also support healthy tooth enamel.51,52 In addition, the catechins and theaflavins in tea may help prevent oral cancer and dental caries.53

Americans are often looking for a quick fix for overweight and obesity, and scientists have been searching for a cure for the crisis for quite some time. While many factors are to blame, poor nutrition and lack of physical activity are often in the spotlight. In its pure (without added sugar), brewed form, tea is a great addition to any diet. It is virtually calorie free and has several potential health benefits associated with its consumption. Preliminary research shows that tea may also affect body weight, fat accumulation, and insulin activity. An in vitro USDA study using a fat cell assay found that tea increased insulin activity by more than 15-fold. Green, black, and oolong tea all yielded similar results. High-performance liquid chromatography showed that the components of tea that enhanced insulin action include EGCG followed by epicatechin gallate, tannins, and theaflavins.54

Preliminary research on tea and fat loss has shown that green tea extract may show the most promise. Green tea has two potential thermogenic components: caffeine and catechin polyphenols (particularly EGCG). While the exact mechanism regarding how green tea increases thermogenesis is uncertain, it is believed that the catechin-polyphenols in green tea contribute to increased circulating levels of norepinephrine through the inhibition of catechol-O-methyl-transferase (the enzyme that degrades norepinephrine).

Why is this important? Norepinephrine (as well as epinephrine) increases both triacylglycerol (stored fat) and glycogen degradation. In addition, researchers believe the interaction between catechin-polyphenols and caffeine contributes to the thermogenic properties of green tea.55 Green tea extract was found to significantly increase 24-hour energy expenditure and fat oxidation in healthy men. In moderately obese patients, three months of consuming green tea extract decreased body weight by 4.6% and waist circumference by 4.48%.56 Though green tea extract may help boost fat and weight loss, it should be used in moderation. One very recent study has indicated that, in highly concentrated doses, green tea polyphenols may pose a health risk. This in vivo study showed cellular hepatotoxicity.57

Thus far, the research on brewed tea is positive. Myriad epidemiology studies support the health benefits of tea consumption in various populations. It remains unclear whether many of the chilled, processed tea drinks on the market contribute to good health. A Consumer Reports study found that instant teas had significantly less antioxidant activity than brewed tea, and bottled teas even less than instant teas. However, if these drinks are preferred, it makes sense to choose one prepared from real brewed tea leaves so the chances of obtaining the benefits from tea consumption are increased.

— Marie Spano, MS, RD, is an exercise physiologist; vice president of the International Society of Sports Nutrition (ISSN); spokesperson for the Tea Council of the USA and the ISSN; and a freelance writer, consultant, and speaker in the nutrition, fitness, and health industries.

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Varieties of Tea: Black, Oolong, Green, and White
The basic varieties of hot tea include green, black, oolong, and white, all of which have varieties of their own. While all come from the same leaf (Camellia sinensis plant), they are produced differently.

Black tea is still the most often sold in the United States. It is fermented and more processed (hence the black color) than the other kinds of tea listed below.

Oolong tea is semi-fermented and heated and dried more than green tea but less than black. In the United States, it is often served alongside dishes in Chinese restaurants. Oolong tea varies in flavor depending on how long the leaves are fermented. It can be found in strong/dark; medium-bodied jade oolong; and pouchong, which is similar taste-wise to green tea.

Green tea is unfermented and undergoes very little processing. It has a light taste without the bitterness associated with black tea. Green tea is very popular in Japan and China. Varieties include Gunpowder, Hyson, Dragon Well, Sencha, and Matcha.

White tea undergoes very little processing and the leaves are unfermented. To produce white tea, the leaves are picked and harvested before they open fully, contrary to the aforementioned teas. White tea is light in color and flavor and is sometimes combined with citrus or melon accents.

— MS

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39. Isemura M, Saeki K, Kimura T, et al. Tea catechins and related polyphenols as anti-cancer agents. Biofactors. 2000;13(1-4):81-85.

40. Zheng W, Doyle TJ, Kushi LH, et al. Tea consumption and cancer incidence in a prospective cohort study of postmenopausal women. Am J Epidemiol. 1996;144(2):175-181.

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45. Curhan GC, Willett WC, Speizer FE, et al. Beverage use and risk of kidney stones in women. Ann Intern Med. 1998;128(7):534-540.

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50. Kamath AB, Wang L, Das H, et al. Antigens in tea-beverage prime human Vgamma 2Vdelta 2 T cells in vitro and in vivo for memory and nonmemory antibacterial cytokine responses. Proc Natl Acad Sci USA. 2003;100(10):6009-6014.

51. Sarkar S, Sett P, Chowdhury T, et al. Effect of black tea on teeth. J Indian Soc Pedod Prev Dent. 2000;18(4):139-140.

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