Additional New Findings Strengthen Link Between Tea and Decreased Risk of Certain Types of Cancer
WASHINGTON, Sept. 24 /PRNewswire/ -- Leading scientists from around the globe convened yesterday in Washington, DC for the Third International Scientific Symposium on Tea & Human Health: Role of Flavonoids in the Diet to review the latest findings on the potential health benefits of tea, including new studies on promoting heart health and reducing the risk for cancer. The latest data provide further evidence of tea's potential disease-fighting capabilities. Major research developments since the Second Symposium on Tea & Human Health, held in 1998, include new results that suggest:
- Tea may reduce Low Density Lipoprotein (LDL, or "bad" cholesterol) levels by 10 percent
- Consumption of as little as four cups of tea per day may contribute to cardiovascular health by improving endothelial function, as seen in clinical studies
- Tea may reduce oxidative stress, as indicated by decreases in DNA damage in smokers
- Tea consumption is linked with a 60 percent decrease in rectal cancer among women
The symposium, which was sponsored by the American Cancer Society, the American College of Nutrition, the American Health Foundation, the American Society for Nutritional Sciences, the Food and Agriculture Organization, the Linus Pauling Institute and the Tea Council of the U.S.A., was held at the United States Department of Agriculture (USDA). Leading researchers from around the world joined American scientists in presenting the latest clinical, laboratory and epidemiological data on the role of tea in promoting healthfulness and reducing the risk of disease.
"As investigators continue to study the multiple effects that tea has on human health, more research supports tea's potential in helping to reduce the incidence of major diseases," said the meeting's co-chair, Jeffrey Blumberg, PhD, Professor, Friedman School of Nutrition Science and Policy and Chief, Antioxidants Research Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston. "The scientific community is making tremendous strides in discovering the potential for flavonoids in black and green tea and other plant foods to promote health and reduce the risk of certain chronic diseases, findings which could have significant implications for public health."
Studies Suggest Tea Consumption May Lower "Bad" Cholesterol
The results of a new clinical study suggest that tea consumption may decrease LDL cholesterol by 10 percent when combined with a "Step I" type diet, moderately low in fat and cholesterol, as described by the American Heart Association and the National Cholesterol Education Program. The study, conducted at the USDA Beltsville Human Nutrition Research Center in Beltsville, MD, is the first investigation of tea in which the subjects' diets were precisely controlled by having them eat meals prepared at the research facility. In addition to the "Step I" diet, all subjects consumed five cups of either caffeinated tea, a placebo beverage with color and flavor closely matching that of the tea, but having no caffeine, or a similar placebo beverage with caffeine added to the same concentration as in the tea. "This clinical trial is one of the first to show significant benefits of tea on blood cholesterol," said Joseph Judd, PhD, Acting Director, Beltsville Human Nutrition Research Center, and the study's lead researcher. "The controlled diet allowed us to closely examine the effects of tea drinking in conjunction with a healthy diet on cholesterol levels free from the interference by variation in other nutrients or components of the diet."
These new developments in tea research add to the growing body of evidence suggesting that tea consumption positively impacts cardiovascular health in several different ways, with as little as two to four cups per day. Another study, published in the May 6, 2002 issue of Circulation: Journal of the American Heart Association, found that study participants who drank four cups of tea per day had a significantly lower risk of death following a heart attack. Additional research suggests that tea flavonoids may support endothelial function, an important indicator of cardiovascular health. More research is necessary to conclude that tea may be used as a preventive measure to combat the risk of heart disease, but the results so far are extremely promising.
New Developments in Cancer Research
In the first intervention study using tea, preliminary findings suggest that smokers who drank tea had significantly lower levels of oxidative DNA damage. Oxidative stress to DNA is implicated in a multitude of chronic diseases, including cancer. In this clinical study, smokers drank four cups of decaffeinated green tea, decaffeinated black tea or water for four months. Researchers then looked at several biomarkers of oxidative stress, or DNA damage. Preliminary results found that smokers who drank green tea showed a significant decrease in urinary biomarkers of oxidative DNA damage. Researchers have also observed similar results in animal studies, in which tea inhibited tobacco-induced lung tumor formation. "We know that smokers' bodies sustain a high level oxidative damage and are at risk for certain cancers," said Iman Hakim, MD, PhD, MPH, Division Director, Health Promotional Sciences, Arizona Cancer Center and Research Associate Professor of Public Health, College of Public Health, University of Arizona. "Because this population has elevated levels of oxidative damage at baseline, we are better able to observe the effects that tea consumption has on oxidative stress."
According to an epidemiological study conducted in Russia to determine the protective nature of black tea against rectal cancer, women who consume high levels of tea were shown to have a 60 percent reduction in the risk of rectal cancer, as compared to women who drank relatively low amounts of tea. Researchers identified patients recently diagnosed with rectal cancer and questioned them about their tea-drinking habits, then divided the participants into three groups based on the amount of dry tea used per month: low consumption, less than 80g dry tea per month; moderate consumption, 80-160g dry tea per month; and high consumption, more than 160g dry tea per month. The Russian population was selected, not only because tea drinking is an essential part of the culture, but also because of the traditional method in which tea is prepared. As is the custom, black tea is brewed at a high concentration, then consumed in a diluted form throughout the day. Instead of measuring tea consumption in terms of fluid measures, intake was measured by the amount of dry tea used to make the tea concentrate. In addition to the 60 percent reduction in risk of rectal cancer found in heavy tea-drinking women, researchers found that women who were moderate tea-drinkers had a 52 percent reduction in the risk of rectal cancer as compared to women in the low consumption group. Although men were also recruited for the study, the findings were much weaker, possibly due to the men's high volume of alcohol intake.
These new findings are an important step in determining the potential role of tea components in cancer prevention and complements previous studies that have found tea drinking to be associated with a decreased risk of certain cancers. More research is necessary before a definitive link can be made, but the current research looks promising.
Mechanism of Action and Bioavailability of Tea Flavonoids
While the established body of tea research strongly suggests that tea consumption offers a wide variety of health benefits, ranging from the promotion of heart health and reduced risk of some forms of cancer, the actual mechanisms by which the benefits are wrought remains under investigation. In vitro studies suggest that tea flavonoids protect against oxidation, but there may be other mechanisms by which tea components function once they are absorbed into the body.
During digestion, flavonoid molecules undergo biochemical changes. Since these compounds are modified in the gut, flavonoids may still protect against oxidative stress, but may function by other mechanisms as well in vivo. In vivo studies suggest that flavonoids interrupt the pathway of oxidative stress and intercept the "message" for apoptosis, or cell death.
Black tea's flavonoids are complex in structure and appear to be absorbed at different points in the body. Some of the larger molecules are not absorbed in the stomach or small intestines, but remain intact until they reach the colon, where they are partly absorbed into the bloodstream. The remaining flavonoids may act as antioxidants and reduce the risk of colon cancer. Because black tea's flavonoids remain intact through much of the gastrointestinal tract, it seems that the flavonoids may have potential benefits at various points throughout the gut. Conversely, the principle constituents of green tea, are simple flavonoids, called catechins, which are quickly absorbed into the body after consumption. "Because green and black tea flavonoids appear to be absorbed and metabolized at different points throughout the digestion process, flavonoids may have an even wider range of protective benefits to various body systems than originally thought," explained Dr. Blumberg.
Looking Toward the Future
The ongoing scientific exploration of the health benefits of drinking tea has led to a growing body of research that points to tea as being an important contributor to overall health. Research continues to show that flavonoids seem to have a potent effect in maintaining the health and function of cells and physiological systems -- and tea is a major source of flavonoids in the human diet.
"The research presented at this year's symposium further extends the scientific evidence that tea may have a favorable effect on the cardiovascular system and may positively impact health in many other ways, including reducing the risk for some cancers," said Dr. Blumberg.
Looking towards the future, researchers plan to probe deeper into the various mechanisms by which tea flavonoids function in the body and the implications these mechanisms have on human health and disease prevention. Clinical trials now underway and being planned will provide further important information about the role of tea in health promotion.