Tea and Health

What avid tea drinkers have appreciated for thousands of years, is now being explained scientifically from specific studies on the health benefits of tea.  On September 18, 2007, the U.S. Department of Agriculture in Washington D.C. hosted the Fourth International Scientific Symposium on Tea and Human Health at which leading scientists from around the world presented the most recent research findings on the topic of tea and health.

The newest area of scientific studies is the impact of tea on the brain.  According to John Foxe, Ph.D., Professor of Neuroscience, Biology and Psychology at City College of the City University of New York, theanine from tea seems to actively alter the attention networks of the brain.  The amino acid theanine, which is almost exclusively present in the tea plant, Camellia sinensis, affects the brain’s neurotransmitters and increases alpha brain-wave activity.  This alpha brain rhythm shows a calmer yet more alert, state of mind.  The effects of theaninine combination with caffeine are higher than with either one alone in improving attention.  Theanine seems to work synergistically with caffeine to help induce a more calming, relaxed state which allows the mind to focus and concentrate better at tasks.  This may explain why tea drinkers feel a soothing effect from tea without necessarily feeling tired.  As Dr. Foxe explained, theanine helps the tea drinker control one’s attention.  When asked if this might be of help to children or adults suffering from attention deficit disorders such as ADD or ADHD, Dr. Foxe agreed, however, so far no studies have been done in that area.

Another positive effect on the brain is the preventive effect of antioxidants in green tea on diseases such as Alzheimer’s and Parkinson’s.  Polyphenols appear to prevent brain cells in mice from dying and may even rescue the neurons once they have been damaged, to help them repair themselves.

Studies on the bioavailability of tea indicate that adding citrus juices to tea increases the body’s ability to absorb the healthy antioxidants in tea.  So adding a slice of lemon to the tea, as the Russians taught us hundreds of years ago, or preparing an iced tea punch with oranges or grapefruits, will make the drink no only pleasing but also healthier.

Tea flavonoids are thought to support cardiovascular health by reducing inflammation and blood cholesterol levels and by dilating blood vessels to help manage blood pressure.  Other exciting findings were the positive effects of tea flavonoids on the prevention of lung cancer and tea’s ability to change metabolism to favor weight loss and better manage blood sugar levels.

The scientists agreed that 2-4 cups of tea would be a healthy daily dose, but also emphasized that tea should be included as part of a “healthy cocktail” consisting of the recommended 5-a-day vegetables and fruits, exercise, intellectual activities, and possibly a glass or two of red wine, and an occasional piece of dark chocolate.

 Recent research exploring the potential health attributes of tea is leading many scientists to agree that tea, both black and green, may contribute positively to a healthy lifestyle.

"Fruits, vegetables, and tea all contain important antioxidants. Research suggests these phytonutrients may contribute substantially to the promotion of health and the prevention of chronic disease. For example, recent research studies reveal the antioxidants in tea may inhibit the growth of cancer cells and support cardiovascular health," stated Jeffrey Blumberg, Ph.D., F.A.C.N, Chief of the Antioxidants Research Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University.

Recent studies have explored the potential health benefits of tea in humans and animal models, and through in vitro laboratory research. For the most part, studies conducted on green and black tea, which are both from the Camellia sinensis plant, have yielded similar results. Research suggests that tea and tea flavonoids may play important roles in various areas of health and may operate through a number of different mechanisms, which are still being explored.

The antioxidant properties of tea flavonoids may play a role in reducing the risk of cardiovascular disease by decreasing lipid oxidation, reducing the instances of heart attacks and stroke, and may beneficially impact blood vessel function, an important indicator of cardiovascular health.

Tea flavonoids may lower the risk of certain cancers by inhibiting the oxidative changes in DNA from free radicals and some carcinogens. Tea may also promote programmed cell death, or apoptosis and inhibit the rate of cell division, thereby decreasing the growth of abnormal cells.

Tea-drinking has been associated with oral health and bone health

Compounds in tea other than flavonoids have been shown to support the human immune system.

The Role of Tea in Cardiovascular Health

Human population studies have found that people who regularly consume three or more cups of black tea per day have a reduced risk of heart disease and stroke. Clinical studies suggest that the risk reduction associated with black tea consumption may be due to improvement in some risk factors for cardiovascular disease, including cholesterol levels, blood vessel function and a reduction in oxidative damage.

While researchers are still examining the various mechanisms by which tea flavonoids function, some studies suggest multifunctional mechanisms, meaning that several mechanisms work in tandem to collectively improve markers for cardiovascular health. Important areas of tea and cardiovascular health research include blood vessel and endothelial function, or the ability of the blood vessels to dilate to allow for proper blood flow, serum cholesterol levels and low density lipoprotein (LDL) cholesterol oxidation. Each of these factors impact the risk of myocardial infarctions (heart attacks), stroke and cardiovascular disease.

Cholesterol

Researchers from the United States Department of Agriculture (USDA) studied the effect of tea on 15 mildly hypercholesterolemic adult participants following a "Step I" type diet moderately low in fat and cholesterol, as described by the American Heart Association and the National Cholesterol Education Program. After three weeks, researchers found that five servings of black tea per day reduced LDL ("bad") cholesterol by 11.1% and total cholesterol by 6.5% compared to placebo beverages.

Tea's Role in Cancer Risk Reduction

Preliminary research suggests that the flavonoids in tea could play a role in human cancer risk reduction, possibly by combating free radical damage, inhibiting uncontrolled cell growth (cell proliferation), and by promoting programmed cell death (apoptosis). Leading scientists worldwide are actively studying these potential mechanisms and clinical trials and population studies are underway. More evidence is needed before any definitive conclusions can be drawn. Recent findings include:

A recent study found that smokers who drank four cups of decaffeinated green tea per day demonstrated a 31% decrease in biomarkers of oxidative DNA damage in white blood cells as compared to those who drank four cups of water. Oxidative DNA damage is implicated in the development of various forms of cancer.

Epigallocatechin gallate (EGCG) may protect normal cells from cancer-causing hazards as well as eliminate cancer cells though apoptosis. Researchers tested the potential anti-cancer benefits of green tea polyphenol, EGCG, in hamster cells and discovered that EGCG suppressed DNA changes and damage from carcinogens. EGCG also protected from further damage from the carcinogens and inhibited growth and multiplication of cancer cells.

Tea’s Role in Immune Function

Researchers from Brigham and Women’s Hospital and Harvard University recently published novel data indicating that tea contains a component that can help the body ward off infection and disease and that drinking tea may strengthen the immune system.  The researchers identified a substance in tea, L-theanine, which primes the immune system in fighting infection, bacteria, viruses and fungi. A subsequent human clinical trial showed that certain immune cells of participants who drank five cups of black tea a day for two to four weeks secreted up to four times more interferon, an important part of the body’s immune defense, than at baseline. Consumption of the same amount of coffee for the same duration had no effect on interferon levels. According to the authors, this study suggests that drinking black tea provides the body’s immune system with natural resistance to microbial infection.

Tea's Role in Oral Health

Tea may also contribute to oral health. The flavonoids in tea may inhibit the plaque-forming ability of oral bacteria and the fluoride in tea may support healthy tooth enamel.
A recent study conducted at the New York University Dental Center examined the effects of black tea extract on dental caries formation in hamsters. Compared to those who were fed water with their food, hamsters that were fed water with black tea extract developed up to 63.7% fewer dental caries.

Tea and Obesity

Preliminary research suggests that drinking tea may have effects on body weight, fat accumulation and insulin activity.

Tea and Reduced Risk of Kidney Stones

Increased intake of fluids is routinely recommended for people who have had kidney stones to reduce the likelihood of recurrence. A recent study that followed 81,093 women for eight years suggests that beverage choice may also affect kidney stones development. The study found that for each eight-ounce cup of tea consumed daily by female participants with no previous history of kidney stones, the risk of developing stones appeared to be lowered by 8%. An earlier study of 45,289 men reported a similar relationship, suggesting that for each eight-ounce serving of tea consumed daily, a 14% decrease in risk of stone development was observed.

Tea and Reduced Risk of Osteoporosis

Although high caffeine intake has been suggested to be a risk factor for reduced bone mineral density (BMD), research indicates that that drinking tea does not negatively affect BMD, and while it may be too soon to state definitively, findings suggest that tea may even play a role in bone health. A study published recently in theAmerican Journal of Clinical Nutrition found that older women who drank tea had higher BMD measurements than those who did not drink tea. The researchers concluded that the flavonoids in tea might influence bone mass and that tea drinking may reduce the risk of osteoporosis. Another recent study found that habitual tea-drinking was seen to have a significant beneficial effect on the BMD of adults (30 years and older), especially in those who had been habitual tea-drinkers for six or more years. Studies in adolescent and postmenopausal women found no relationship between caffeine intake and bone health.