Research Papers on the Health Benefits of Tea Part 1
HEALTH BENEFITS OF TEA - SCIENTIFIC STUDIES
Tea has been shown to have many benefits to health in studies that have been carried out over the past few years. In a study of over 40,000 Japanese adults enrolled in the Ohsaki National Health Insurance Cohort Study initiated in 1994, it was found that those who drank five or more cups of green tea a day had a death rate that was 26% lower than non-tea drinkers at seven years into the study, and 16% at eleven years. Green tea was particularly effective in reducing the risk of heart disease, but did not apparently reduce the risk of cancer. (Green tea consumption and mortality due to cardiovascular disease, cancer and all causes in Japan. JAMA. 2006; 296:1255-1265). A study of 1003 Japanese men indicates that higher consumption of green tea is associated with a lower prevalence of cognitive impairment. Less benefit was found for black and oolong tea, and no benefit from coffee. (Green tea consumption and cognitive function: a cross-sectional study from the Tsurugaya Project. Am J Clin Nutr 2006; 83: 355-61). In a Chinese study, women who drank tea daily were found to have a significantly reduced risk of developing biliary stones or gallbladder cancer. Among men, who were more likely to be cigarette smokers, there was a slight non-significant reduction of risk. (Tea drinking and the risk of biliary tract cancers and biliary stones: a population-based case-control study in Shanghai, China. Int J Cancer 2006; 118: 3089-94).
The British Medical Journal has published a Japanese study on the benefits of green tea consumption in preventing cardiovascular disease, liver disorders and possibly cancer. The study, begun in 1986, concerned 1371 men over the age of 40 (Cross sectional study of effects of drinking green tea on cardiovascular and liver diseases BMJ 1995;310:693-696, 18 March) . Tea consumption was classified as less than 3 cups, between 4 and 9 cups, and over 10 cups per day. It was found that consumption of green tea was significantly associated with lower serum concentrations of lipids and lipoproteins. "An increase in consumption substantially decreased serum total cholesterol and triglyceride concentrations, and this strong association remained almost unaltered even after age, cigarette smoking, alcohol consumption and relative body weight were controlled for". Interestingly it was found that those who drank the most green tea (more than 10 cups) were also the heaviest smokers, but that whilst levels of lipid peroxides were generally higher among smokers than non-smokers, those smokers who drank more than 10 cups had lipid peroxide levels similar to non-smokers. The study also showed that consumption of green tea reduced liver cell damage and resulted in slightly lower (but not abnormal) haemoglobin concentration. The study also suggests that green tea has protective effects on the development of cancer.
MILK IN TEA?
The debate continues, while the European Heart Journal online, January 9th, 2007 says that adding milk to tea negates its benefits in preventing cardiovascular disease. The caseins (proteins) in the milk interact with the catechins in the tea which are responsible for its protective effects. Sixteen postmenopausal women were asked to drink half a litre of tea (either freshly brewed black tea or black tea with 10% skimmed milk) or boiled water at three different sessions. Ultrasonography was used to measure brachial artery cell function in the forearm before and after consumption. Black tea significantly improved the ability of the arteries to soften and relax, an effect which disappeared when the tea was taken with milk. The milk also destroyed the antioxidant effects of the tea.
On the other hand, A Dutch study (Eur J Clin Nutr 2000; 54:87-92 and 1996;50:28-32) has shown no apparent difference, contradicting a previous study that appeared to show some diminishing of antioxidant activity when milk was added. The debate continues.
GREEN TEA & ALZHEIMER'S
Epigallocatechin-3-gallate (EGCG), an ingredient of green tea, has been found to significantly reduce production of beta-amyloid, an Alzheimer's-related protein, which can accumulate abnormally in the brain and lead to nerve damage and memory loss. The reduction in beta-amyloid was found in both cell cultures and mouse brains. (J Neurosci 2005; 25: 8807 - 8814).
GREEN TEA & ARTHRITIS
Drinking green tea could help keep arthritis at bay, say scientists. Researchers at the University of Sheffield have found that two compounds found in green tea can help prevent osteoarthritis by blocking the enzyme that destroys cartilage. Green tea, first discovered in China nearly 5,000 years ago, has long been thought to be beneficial to health. The Arthritis Research Campaign, which partly funded the research, said the initial results were promising. A spokeswoman said: "These findings are of great interest, and although further research needs to be done, in the mean-time people should drink green tea as it's not going to do them any harm - and may in fact do them a lot of good." (BBC News 15 February, 2003).
GREEN TEA & RHEUMATOID ARTHRITIS
Studies in mice suggest that green tea antioxidants may have a powerful effect in reducing the incidence and severity of rheumatoid arthritis. Polyphenols (antioxidants found in green tea) possess much more potent antioxidant activity than well-known antioxidants such as vitamin C and vitamin E. A research team from Western Reserve University, Cleveland, Ohio has now focused on the effect of these polyphenols in rheumatoid arthritis. Mice used in the Cleveland study were fed either plain water or water enriched with green tea polyphenols, with dosages roughly equivalent to a human drinking four cups of green tea per day. Each of the mice were then injected with collagen, rendering them vulnerable to collagen-induced arthritis - a condition very similar to human rheumatoid arthritis. The study showed that mice fed green tea polyphenols "were significantly less susceptible to the development of collagen-induced arthritis, and if they developed arthritis, the disease was late in onset and mild in comparison to mice not given green tea polyphenols". (Proceedings of the National Academy of Sciences 1999;96:4524-4529 ). Meanwhile a US study has shown that drinking at least one cup of tea a day can reduce the risk of heart attack by 44%. The health benefits are thought to be derived from ingredients known as flavonoids, a type of antioxidant found in all types of tea. Flavonoids are thought to neutralise the effect of free radicals, a highly reactive molecule which travels around the body causing chemical reactions which can damage cells, including those in the heart tissues. A previous Dutch investigation of more than 800 men between 65 and 84 showed that drinking even more tea - between three and four cups a day - decreased risk of death from coronary heart disease by 58%. In 1991 there were just 153 studies on tea, while in 1998 there were 625 published papers. In a further Japanese study, tea without sugar has been found to be good for teeth and gums. Tea contains tannin fluoride which appears to help prevent plaque. "An increase of just one cup a day could prove invaluable in the fight against gum disease," said the British Dental Health Foundation.
GREEN TEA & ATHEROSCLEROSIS
Twenty smokers who drank green tea for four weeks showed improvement in markers of atherosclerosis (reductions in soluble P-selection levels and concentrations of oxidised LDL. (Clin Biochem 2005; 38: 84-7).
GREEN TEA MAY SUPPRESS AUTOIMMUNITY
Stephen Hsu, probably the world's leading researcher into green tea and a former green tea farmer himself, has presented a preliminary study indicating that EGCG, present in green tea, can help suppress proteins that trigger autoimmune responses. (Arthritis Foundation's Arthritis Research Conference, 2005, Atlanta).
TEA & IMMUNITY
A study carried out at Brigham and Women's Hospital and Harvard Medical School has indicated the mechanism by which tea is able to help fight infections. Immune T cells in the body can recognise antigens such as those found in tumour cells, bacteria, parasites and fungi, and then stimulate the production of antibodies to fight infection. Once exposed to antigens, the T cells remember them when exposed again, thus developing immunity. Now similar antigens have been found in tea, and the researchers discovered that the tea antigens tea were able to prime the T cells to remember how to respond to subsequent antigens, even when the source of the antigens was bacterial, thus helping to provide natural resistance. (Proceedings of the National Academy of Sciences).
GREEN TEA & COGNITIVE DECLINE
Regular green tea consumption appears to be associated with a reduced risk of cognitive decline, according to a study of more than 1000 Japanese adults in their 70s. Those who drank two or more cups of green tea a day were half as likely to show signs of cognitive impairment as those who drank three cups or less a week, with an average of one cup a day showing a risk roughly halfway between the two other groups. Although the study was not able to demonstrate a clear connection between drinking green tea and maintaining mental acuity, it may help explain why there is less dementia, especially Alzheimer's disease, in Japan compared to Europe and North America. (Kuriyama S et al. Green tea consumption and cognitive function: a cross-sectional study from the Tsurugaya Project 1. Am. J. Clinical Nutrition, Feb 2006; 83: 355-361).
GREEN AND BLACK TEA & DIABETES
Green and black tea fed to rats for three months had a blood-sugar-lowering effect and inhibited the development of diabetic cataracts. (J. Agric. Food Chem., 53 (9), 3710 -3713, 2005).
TEA MAY REDUCE BODY WEIGHT
Thirty-eight men were assigned to one of two groups, and were asked to drink a bottle of oolong tea daily, containing either 22mg or 690mg of catechins. After twelve weeks the high catechin group showed a significant reduction in body mass index, waist circumference and body-fat mass compared with the low dose group. (Am J Clin Nutr 2005; 81: 122-9).
CHOLESTEROL & WEIGHT-LOSS
According to Dutch research, drinking tea protects against the build-up of cholesterol in the arteries, especially in women. Results indicated that people who drank one to two cups of tea a day were 46% less likely to develop severe atherosclerosis, rising to 69% in those who drank four cups of tea a day. The protective benefit of tea was most pronounced among women. The authors acknowledge that at least in the West, people who drink tea generally have a healthier lifestyle and diet, which may account for the findings. In this study, for example, the researchers found that people who drank more tea tended to be lean, had a healthy diet, and smoked less. However the fairly high levels of antioxidant flavonoids in black tea are thought to protect against arterial plaques, the fatty deposits that clog arteries, by preventing fat from being deposited on artery walls (Archives of Internal Medicine 1999;159:2170-2174). Green tea appears to speed up calorie burning, including fat calorie burning, according to researchers from the University of Geneva in Switzerland. The study authors report that, compared with placebo, treatment with green tea was associated with a "significant increase" (+4%) in daily energy expenditure. They believe that the caffeine interacts with the flavonoids in tea to alter the body's use of norepinephrine, a chemical transmitter in the nervous system, and increase the rate of calorie burning (American Journal of Clinical Nutrition, November 1999). In Japan, The Saitama Cancer Research Institute has discovered that women with a history of breast cancer who drank 5 cups of tea daily were 50% less likely to have a recurrence than women who drink none or less than 5 daily cups. In a separate study, drinking strong tannin-rich tea has been shown to benefit genetic haemochromatosis, since tannates and other ligands inhibit the absorption of iron (BMJ no. 7168 (7th Nov '98) p1330).
NEW GREEN TEA MEDICINE FOR HPV
The first prescription botanical drug for half a century has been approved by the US Food and Drug Administration. Veregen, a special extract made from green tea, has been approved for the treatment of genital warts caused by the human papillomavirus (HPV). In two prospective, randomised, double-blind clinical studies of nearly 400 adults with external genital and anal warts, the median time to clear warts completely was 16 weeks and 10 weeks, respectively. Meanwhile a study has shown that tea extracts from both green and black tea can help minimise the damage to skin caused by radiotherapy treatment for head, neck or pelvic cancers, with green tea having the better effect on pelvic cancers. (The effects of tea extracts on proinflammatory signalling. BMC Medicine, published online Nov. 30, 2006).
TEA DRINKING REDUCES HYPERTENSION
Habitual tea drinking appears to significantly reduce the risk of developing hypertension. Of 1507 Taiwanese men and women, 600 were regular tea drinkers, defined as drinking 120ml or more a day. Compared with non-habitual tea drinkers, the risk of developing hypertension decreased by 46% for those who drank 120 to 599 ml a day and was further reduced by 65% for those who drank 600 ml a day or more after adjusting for age, sex, socioeconomic status, family history of hypertension, body-mass index, waist: hip ratio, lifestyle factors (total physical activity, high sodium intake, cigarette smoking, alcohol consumption and coffee drinking) and dietary factors (vegetable, fruit, unrefined grain, fish, milk, visible-fat food and deep fried food intake). (Arch Intern Med 2004; 164: 1534-40).
GREEN CREAM TREATS ROSACEA
In a study of 60 female patients suffering from papulopustular rosacea, half were treated with a hydrophilic cream containing 2% polyphenone (green tea extract) and half to vehicle cream. All women had visible signs of papules and pustules, 20 had erythema, and 17 had telangiectasia. The women randomised to the green tea extract cream had a 70% improvement in rosacea compared with women in the vehicle cream group. (63rd Annual Meeting of the American College of Dermatology, Poster 19).
GREEN TEA & ALLERGIES
Laboratory tests carried out at Kyushu University, in Fukuoka, Japan have demonstrated that a green tea compound (methylated epigallocatechin gallate/EGCG) blocked the production of histamine and immunoglobulin E (IgE), two compounds involved in triggering and sustaining allergic reactions. "Green tea appears to be a promising source for effective anti-allergenic agents," says lead researcher Professor Hirofumi Tachibana. "If you have allergies, you should consider drinking it." (J Agric Food Chem; 2002; 50(20); 5729-5734).
CHINESE TEA HAS ANTI-HELICOBACTER EFFECT
Numerous studies have shown a link between the presence of Helicobactor pylori and a range of gastro-intestinal diseases, including gastric ulcers, Barretts Syndrome and oesophageal cancer. 72 patients awaiting endoscopy were recruited to a study examining the effect on this virus of the consumption of Chinese tea. They each completed questionnaires about their current Chinese tea consumption habits and those when they were around 10-25 years old. This information was used to calculate the tea consumption indices (TCI). Gastric biopsies (two from the antrum and two from the corpus) were taken for histological examination for Helicobacter. Of the 72 patients, 42 (58.3%) were Helicobacter positive. The age, sex ratio and indications for endoscopy were similar in both Helicobacter-positive and -negative groups. Classifying patients using either current, past or total TCI, patients with high tea consumption had significantly lower Helicobacter infection rate than those with low tea consumption (45% compared to 74%, 42% compared to 67% and 40% compared to 83%, respectively). Helicobacter-negative patients had higher overall TCI than Helicobacter-positive patients (28.2:17.3). When current and previous histories were analysed separately, Helicobacter-negative patients also had a trend towards higher TCI currently (16.6:11.0) and in their 20s (11.6:6.1). This seems to indicate that Chinese tea consumption may decrease the chance of Helicobacter infection (Journal of Gastroenterology and Hepatology 2002;17(5):552-555.)
GREEN TEA & STROKE
Gallotannin, a substance found in green tea, is up to 1000 times more powerful than comparable existing medicines in preventing brain damage after stroke. It is the overactivation of a normal DNA repair system (the PARP/PARG system), that causes cells to die after stroke. The PARP/PARG system is activated by the release of cell-damaging oxygen radicals (oxidative stress), and when cells become overexcited by various toxins. Gallotannin acts by blocking the PARP/PARG system and is 100 times more effective than antioxidants at neutralising oxidative stress. It is also effective at blocking brain cell death from chemicals that normally overexcite the cells. The researchers also found comparable results from Nobotanin B, derived from the Brazilian glory bush (Proceedings of the National Academy of Sciences 2001;98:12227). In a separate study carried out in Japan over a ten-year period, consumption of 3 or more cups of green tea a day was shown to reduce the risk of recurrence of breast cancer (Cancer Lett. 2001, 167,175-82).
BLACK TEA AND HEART HEALTH
It is now well known that the antioxidants found in tea can prevent the oxidation of low-density lipoproteins (LDL) that lead to the formation of plaque in artery walls, although very high concentrations of tea flavonoids are needed to produce this effect. A new study has indicated an alternative explanation for the heart benefits of tea, showing that flavonoids improve the function of the vascular endothelium which forms the inner lining of cells in all blood vessels and produces substances that regulate the diameter of the blood vessel. It responds to changes in the body's oxygen and blood flow needs, by causing blood vessels to dilate or contract and further inhibits the formation of blood clots and the development of inflammation in the vessel wall. All these functions may be impaired in individuals with atherosclerosis (endothelial dysfunction). Observation of 50 individuals with coronary artery disease found that tea improved endothelial-dependent dilation in their arteries, whilst water and caffeine alone had no effect. (Circulation: Journal of the American Heart Association, 10/7/01). Meanwhile two new papers supporting the health benefits of drinking black tea were presented at the Epidemiology Congress 2001 in Toronto.
Numerous studies have proven the cardiovascular benefits of green tea. But black tea also has benefits for the heart say researchers from the University of Arizona. A study of 3,430 adults in Saudi Arabia found that those who drank more than 6 cups per day of black tea had a more than 50% lower risk of coronary heart disease compared to tea abstainers, even after adjusting for other factors such as smoking, diet and obesity. Antioxidants called flavonoids, found in both green and black teas, are thought to help reduce blood pressure, hardening of the arteries and the amount of LDL or ‘bad' cholesterol in the blood stream. (Preventive Medicine 2002; 36:64-70).
TEA STRENGTHENS BONES
In a study of 497 men and 540 women, 30 years and older, those with a history of tea consumption of between 6 and 10 years showed higher bone mineral density of the lumbar spine than non tea drinkers, and those with over 10 years history of tea consumption showed the highest bone mineral density in all measured regions of the body. (Arch Intern Med. 2002;162:1001-1006).
GREEN TEA & MUSCULAR DYSTROPHY
Studies on mice indicate that green tea might help slow the muscle degeneration seen in Duchenne muscular dystrophy, possibly by reducing oxidative stress. The lowest effective dose in the study corresponded to seven cups of green tea a day for humans (American Journal of Clinical Nutrition 2002;75:749-753).
INFERTILITY AND TEA
A new study suggests that drinking at least a half cup of tea a day doubles a woman's chances of getting pregnant. The study, reported in the American Journal of Public Health, said that one explanation for this effect may be a chemical component in tea that affects DNA and the fluid that aids a woman's eggs in the fertilization process. No other caffeinated beverage, including coffee and Pepsi Cola, had any impact on the women. The study didn't determine whether green, black or herbal teas are most effective, nor did it separate out the effect of caffeinated and decaffeinated teas. It should be noted that previous studies have suggested that tea can cause miscarriage and more work needs to be done before the benefit is proven.
TEA & TEETH
Drinking tea may help prevent tooth decay. A study carried out at the University of Illinois, USA has shown that bacteria present in dental plaque stopped growing when people rinsed their mouths with black tea five times for 30 seconds over a 15 minute period. It is the poplyphenol components of the tea that fights dental plaque. A previous Swedish study had also confirmed this finding, showing that people who rinsed their mouths with black tea for one minute, ten times a day, had significantly less bacterial plaque than those who used just water.
White tea almost exclusively comes from Fujian Province in China and is so-named because it has a higher proportion of buds to leaves, compared to other tea, and the buds are covered with silver coloured hairs. It is the most minimally processed of all tea varieties, thus reducing oxidation. Research carried out at the Linus Pauling Institute in Oregon, USA, has now shown that white tea is able to prevent mutations of DNA two to five times more efficiently than green or black teas, thus theoretically giving it greater potential in preventing cancer. Additional research into the white tea demonstrated a significant anti-tumour effect in rats genetically prone to colon cancer.
GREEN TEA & THE SKIN
Green tea is already thought to protect against some cancers because it contains antioxidants. A recent review of previous studies finds drinking green tea may help prevent skin cancer - and it may even be effective when added to skin care creams. Researchers at the department of dermatology at Case Western Reserve University, USA, reviewed several studies on green tea and report that it may be useful in preventing and treating a variety of human skin disorders. The substances in green tea thought to protect against cancer are called polyphenols, which have antioxidant properties that can cancel out the damage caused by free radicals. Free radicals are molecules that damage cell DNA and as a result can begin the process of a cell turning cancerous. The researchers say it is better to drink green tea to benefit from its antioxidants, but add that it could be useful if applied topically on the skin. It may protect against damage from environmental pollutants, especially ultraviolet radiation from the sun. "Supplementation of skin care products with green tea may have a profound impact on various skin disorders in the years to come".
TEA IN SKINCARE PRODUCTS
Now we can not only drink green tea but cover ourselves with it. Excited by the proven antioxidant properties of green tea when applied to the skin, cosmetic companies are increasingly using it in their skin products. The Estee Lauder company, for example, currently has nine products that include tea. Japanese research has indicated a correlation between green tea and a reduction in the incidence of skin cancer. Topical application of green tea has been shown to reduce skin damage caused by free radicals such as sun and pollution.
More exciting tea studies continue to pour in. In recent months, the following discoveries have been reported: Epigallocatechin gallate, or EGCG, an antioxidant found in green tea is at least 100 times more effective than vitamin C and 25 times better than vitamin E at protecting cells and their genetic material, DNA, from damage believed to be linked to cancer, heart disease and other potentially life-threatening illnesses, according to research carried out at the University of Kansas Lawrence. The antioxidant has twice the antioxidant benefit of reservatrol, found in red wine. Green tea has another advantage over vitamin E in that excessive amounts of antioxidants found in water soluble green tea are excreted by the body, whilst the body absorbs and retains fat-based vitamins such as vitamin E, even at potentially harmful levels.
Tea drinking increases concentration and the ability to learn, according to research by Kimron Shapiro, a professor of psychology at the University of Wales. It is especially beneficial to people when they are doing two things at once and also helps them concentrate when they are performing one task after another. The research demonstrated that caffeine was not responsible because those drinking tea out-performed those given a caffeine-only drink. Britons drink 185 million cups of tea a day. Powdered and instant tea contains only small percentages of antioxidants compared with freshly brewed tea.
A Chinese study has shown that men who drink at least 1 cup of green tea per week for 6 months have a reduced risk of cancer of the colon, rectum or pancreas (Int. J. Cancer 1997, 70, 255-258). Research at the Karolinska Institute in Stockholm, Sweden has shown that a compound found in green tea can inhibit angiogenesis in mice, the process in which blood vessel growth is stimulated. The finding suggests that the compound may be useful in fighting malignant tumors, which must form new blood vessels in order to grow. Drs. Yihai Cao and Renhai Cao report that green tea, and one of its components, epigallocatechin-3-gallate (EGCG), significantly prevents the growth of new blood vessels in animals. The researchers conclude that long-term consumption of 2 to 3 cups of green tea might inhibit angiogenesis, an effect that may be beneficial in the prevention of cancers as well as other angiogenesis-dependent diseases, such as diabetic retinopathy - an eye disease that is a common cause of blindness. The researchers warn that where angiogenesis is important, as in pregnancy or in patients with healing wounds, people should not drink large amounts of tea. (Nature 1999;398:381-382). Another study has shown that drinkers of one or more cups of black tea a day are 40% less likely to suffer a heart attack than non-drinkers, whilst coffee seems to have no significant effect on heart attack risk (American Journal of Epidemiology 1999;149:162-167). A case-control study of more than 1,200 Canadian men led by researchers at the University of Toronto and recently published in the International Journal of Cancer, investigated the association of prostate cancer with consumption of alcoholic and other beverages, including tea, coffee and cola. Of the beverages studied, only tea consumption (of more than two cups per day) was associated with a decrease in risk of prostate cancer.
GREEN TEA & CANCER
There is considerable research evidence that green tea is associated with reduced risk of various forms of cancer. Now a team of Spanish and British researchers has discovered how epigallocatechin gallate (EGCG), a naturally occurring polyphenol in green tea, binds with a specific enzyme (dihydrofolate reductase/DHFR) which can inhibit cancer cell growth. The enzyme, which is very similar to the drug methotrexate used in chemotherapy has an effect even at low concentrations (the equivalent of two to three cups of green tea a day). ECGC concentrations are five times greater in green tea than black tea, according to the researchers. (Cancer Res. 2005 65: 2059-2064).
GREEN TEA & BREAST CANCER
A meta-analysis of 13 separate studies has indicated that women who have the highest intake of green tea have a 22% lowered risk of developing breast cancer compared to women with the lowest intake. The evidence for the benefits of black tea and breast cancer are not so clear. (Carcinogenesis. 2005;Nov 25).
BLACK TEA & BREAST CANCER
A meta-analysis of studies into the relationship of tea drinking to the risk of developing breast cancer, has found a 20% reduction with high green tea consumption, with no comparable benefit for black tea.
TEA & OVARIAN CANCER
Women who drink two or more cups of tea a day appear to lower their risk of ovarian cancer by 46% compared to women who drink no tea, according to a recent Swedish study. The study found that each additional cup of tea consumed per day was associated with an 18% lower risk of ovarian cancer. (Arch Intern Med. 2005;165:2683-2686).
BLACK TEA REDUCES OVARIAN CANCER RISK
The effect of black tea consumption on ovarian cancer risk was recently investigated. A case-control study included 414 women with primary epithelial ovarian, fallopian or peritoneal cancer and 868 age- and region- matched women with non-neoplastic conditions. Compared to women who did not drink black tea, women with a usual consumption of at least two cups a day experienced a 30% decline in ovarian cancer risk. Similar declines were noted among individuals consuming two or more cups of decaffeinated coffee daily, but no association was noted between any level of caffeinated coffee consumption and risk of ovarian cancer. The authors speculate that the chemoprotective effects of phytochemicals in black tea and decaffeinated coffee may be important, and that these may be counteracted in regular coffee by the elevated risk associated with its higher caffeine content. (Consumption of black tea or coffee and risk of ovarian cancer. Int J Gynecol Cancer. 2007 Jan-Feb;17(1):50-4).
GREEN TEA PREVENTS OVARIAN CANCER
In an Australian study of 254 Chinese patients with epithelial ovarian cancer and 652 healthy controls, it was found that the risk of ovarian cancer declined both with the more tea they drank and the length of time they had been drinking tea, with those drinking tea daily having only 39% of the risk (compared to non tea drinkers) and those who had drunk tea for more than 30 years having a 23% risk. (Cancer Epidemio Biomarkers Prev 2002; 11: 713-18).
BLACK TEA MAY HELP PREVENT ORAL CANCER
Indian research has found that drinking black tea three times a day for a year could help prevent the development of oral cancer in subjects with leukoplakia, a disease that causes white spots to appear on mucous membranes on the tongue and in the mouth. Oral cancer is the single most common malignancy found in Indian men and the third most common among Indian women. The study also found a significant decrease in micronuclei frequency and chromosomal aberrations. (JEnvPathToxOncol.v24.i2.70). The anti-cancer benefits of tea are linked to the presence of water-extractable polyphenols which are much higher in green tea (30-40%) than black tea (3-10%). (Sun CL etal. Green tea, black tea and breast cancer risk: a meta-analysis of epidemiological studies. Carcinogenesis, doi:10.1093/carcin/bgi276).
TEA & PROSTATE CANCER
A new study has confirmed the growing evidence that drinking tea, both green and black, might slow the growth of prostate cancer. The 15 men in this study, who were due for prostate surgery for cancer in five days time, were required to steep the tea for five minutes to ensure the release of epigallocatechin gallate (EGCG) and to drink five cups a day. Another five men, also due for surgery, who drank regular or diet cola containing similar amounts of caffeine and other stimulants as the tea, acted as a control. A comparison of biopsied tissue taken from the prostates of all the men before the study and after surgery revealed that in the tea-drinking men the tissue contained tea polyphenols and reduced polyamines (a marker of rapidly dividing tissue found in prostate and other cancers) while the biopsies of the men who drank cola showed no such changes. (Experimental Biology 2004 Meeting, Washington, December 2005).
GREEN CAN PREVENT PROSTATE CANCER
When substances extracted from green tea were given to 32 men at high risk of developing prostate cancer, only one man had developed the disease one year later, compared to nine men out of a similar group who were given only a placebo. All the men in the study had high-grade prostatic intraepithelial neoplasia - premalignant lesions that are known to predict the development of invasive prostate cancer within one year in nearly a third of all cases. The men in the treatment group were given three 200mg tablets of green tea catechins a day, a dose equivalent to what a typical Chinese tea drinker will consume over one or two days. (96th Annual Meeting of the American Association for Cancer Research, April 2005).
GREEN TEA AND SKIN CANCER
Previous studies have shown that green tea contains powerful anti-oxidants that fight harmful free radicals. This enables green tea to reduce the risk and prevent the development of many cancers. But the effect of green tea is not limited to internal organs. It can also improve the health of the skin by preventing wrinkles, reducing damage from sunburn and even decreasing the risk of skin cancer when applied topically. A recent study reviewed several previous studies that looked at green tea and skin. Green tea taken orally or applied directly to the skin has prevented damage from ultraviolet light, which can lead to skin cancer. Mice exposed to a chemical that causes skin cancer were less likely to develop tumours if they had green tea ointment applied for 1 week prior to exposure. (Archives of Dermatology 2000;136:989-994, 1051).
GREEN TEA & STOMACH CANCER
A joint US-Chinese study carried out in China compared green tea consumption among 133 stomach cancer patients, 166 patients with colonic gastritis and 433 people with no stomach disease. They found that people who drank one to three cups of green tea daily had a 30% lower rate of stomach cancer, whilst those who drank more than three cups had a 61% lower rate (International Journal of Cancer, May 2001).
GREEN TEA AND LEUKAEMIA
Following press reports of studies carried out at the Mayo Clinic, Rochester, Minnesota which found that EGCG was able to kill cancer cells in vitro from patients with chronic lymphocytic leukaemia (CLL), four patients with low grade B-cell malignancies who were attending the clinic independently started taking over-the-counter EGCG products. Now the clinic reports that three of these have shown clear improvements with regression in their cancer. Although spontaneous remission/regression is occasionally observed in individuals with low grade B-cell malignancies, such events are rare. A National Cancer Institute sponsored phase I/II trial of de-caffeinated green tea extracts for patients with asymptomatic, early stage CLL opened at the Mayo Clinic in August 2005. (Leukemia Research, In Press, Corrected Proof, Available online 1 December 2005).