Green Tea and Cancer Prevention Review

April 5th, 2010 by admin 1 comment »

Green tea made from tea plant leaves (Camellia sinensis) has been found to contain flavonoids, which are antioxidants in the polyphenol group that can inhibit cancer cell growth. The most effective flavonoid in cancer prevention is thought to be epigallocatechin-gallate (EGCG).

A review of research concerning the preventative effects of green tea on cancer in humans was conducted by European scientists1. They looked at studies that were available through December 2008 and selected fifty-one studies with 1.6 million participants to include in the review.

All of the studies chosen looked for a link between drinking green tea and cancer cell growth in humans. The majority of the studies focused on cancer of the digestive tract (27) and a few looked at breast, prostate, lung, ovarian, urinary and oral cancers.

Review Results

The reviewers concluded that the results of studies concerning digestive tract cancer were very contradictory. Results from studies on the other types of cancer were variable and generally failed to show a strong link between green tea consumption and a reduced risk of cancer development. Evidence was shown that green tea could reduce the risk of lung cancer (mostly in men) and urinary bladder cancer. But there was also information that green tea consumption could increase the risk of bladder cancer.

More Recent Review

Another review of academic literature conducted in July 2009 reported more than 1100 publications existed concerning the effect of polyphenols, the group of antioxidants that includes flavonoids, on cancer2. During the same time period the scientists also searched the PubMed database using the keywords “polyphenols – cancer – review” and received more than 320 relevant reviews.

This review identified that a prevalence of cancer research focused on the “targeted therapy approach”. They went on to search the PubMed database with the keywords “polyphenols – cancer – kinases” and found more than 130 results and half of them were published after 2003.

One aspect of the targeted therapy approach is targeting specific protein kinases to fight cancer.3 They inhibit tumor growth and prevent inflammation which is thought to cause some types of cancer. These results prove promising that scientists are moving forward in the quest to better understand the beneficial qualities of green tea when used medicinally.

It seems there was not enough strong evidence up until the end of 2008 to conclude that drinking green tea will prevent any type of cancer. However, since that time there have been numerous studies looking at the benefits of green tea with regard to cancer prevention and control.2 Although studies and reviews have produced mixed results, as scientists gain new information about the beneficial effects of green tea, research continues to be conducted. Scientific research is a process of elimination and advances in learning about are leading to continued study.2,3

1Green tea (Camellia sinensis) for the prevention of cancer. Boehm K, Borrelli F, Ernst E, Habacher G, Hung SK, Milazzo S, Horneber M. 2009. Cochrane Database System Rev. Jul 8;(3)

2Natural Polyphenols that Display Anticancer Properties through Inhibition of Kinase Activity.

Lamoral-Theys D, Pottier L, Dufrasne F, Nève J, Dubois J, Kornienko A, Kiss R, Ingrassia L. 2010. Curr Med Chem. 2010 Feb 16. [Epub ahead of print]

3Chemoprevention with phytochemicals targeting inducible nitric oxide synthase. Murakami A. 2009. Forum Nutr. 61:193-203. Epub 2009 Apr 7.

Green Tea and Breast Cancer

March 31st, 2010 by admin 1 comment »

Green Tea and Breast Cancer

Breast cancer is the most prevalent form of cancer in women the world over. Green tea made from tea plant leaves (Camellia sinensis) has been found to contain flavonoids, which are antioxidants in the polyphenol group.

The results of surveys comparing medical histories between green tea drinkers and non-drinkers show that green tea can inhibit breast cancer cell growth. The most effective flavonoid in cancer prevention is thought to be epigallocatechin-gallate (EGCG).

A Review of Published Studies

A lot of research has been conducted since 1998 about the effects of green tea on breast cancer. This is because many studies, whether epidemiological, molecular or clinical have generated results proving that green tea has some anti-inflammatory and anti-cancerous properties. AA Ogunleye and his colleagues conducted a systematic search of studies of breast cancer risk and recurrence that were published between 1998 and 2009.1

The researchers used 5 databases of published studies and found 5617 cases of breast cancer. Of those cases, they pinpointed 7 studies of breast cancer incidence and 2 studies of breast cancer recurrence that included green tea consumption as a variable. There was a great deal of variation in the results. They concluded there is probably a beneficial effect of green tea on breast cancer even though the studies were so variable. There is a clear need for more studies under controlled conditions to make any definitive conclusions.

A literature review of the effects green tea, green tea extract or its purified polyphenol (-)-epigallocatechin-3-gallate (EGCG), an antioxidant, on health benefits was conducted by Y. Clement, from the University of the West Indies.2 Data was gleaned from 2 electronic databases: PubMed (1966 to 2009) and the Cochrane Library (Issue 4, 2008). Although observations were made from observational studies Clement concluded there are trends toward green tea assisting in the prevention of breast cancer incidence.

Green tea has proved to have anti-tumor ability. In a laboratory experiment, cells infected with human breast cancer cells grew cancerous tumors. Following cell treatment with green tea polyphenols or EGCG tumor growth was inhibited and tumor cells were killed.3

A current experimental study looked at the effect of green tea on the efficacy of a common chemotherapy drug, paclitaxel, with taxol as the active ingredient.4 Taxol is extracted from the bark of the Pacific yew tree (Taxus brevifolia). Over time, cancer cells can develop resistance paclitaxel. The identification of “chemosensitizers”, substances that make cancer cells more susceptible to chemotherapy treatment, is vital for cancer treatment as the second decade of the 21st century begins.

One such chemosensitizer has proven to be EGCG extracted from green tea. Researchers compared cancer cell death when treated with the chemotherapy drug paclitaxel alone, with EGCG alone or paclitaxel and EGCG in combination. The combination of the two substances showed the most significant effect on tumor destruction than either one alone (a synergistic effect).

Common stumbling blocks when using natural chemicals, such as polyphenolic compounds, in the human body are bioavailability and instability in the living system. The chemicals may be stable and bioavailable until the compound is introduced to the body. There are many reactions the natural chemicals are subject to and the environment within the body may not be hospitable for them.

So along with the development of chemosensitizers for use in disease treatment, “prodrugs” are sometimes required to maintain the viability of the treatment under physiologic conditions. Researchers have developed a prodrug of EGCG called Pro-EGCG (1) to increase the stability, bioavailability and anticancer activities of EGCG.5

EGCG is unstable in the body and is poorly bioavailable. The researchers, when trying to create a prodrug for EGCG, added chemical groups to the areas on the molecule that are available to react with other molecules. The researchers named the new molecule Pro-EGCG (1). Now the EGCG can be protected by preventing other molecules from attaching to it and forming completely different molecules that would likely not have anti-cancerous effects. EGCG and Pro-EGCG (1) given in combination enhances tumor cell death and growth suppression and has potential use in preventing and treating cancer.

1Green tea consumption and breast cancer risk or recurrence: a meta-analysis.

Ogunleye, AA, Xue F, Michels KB. Breast Cancer Res Treat. 2010 Jan;119(2):477-84. Epub 2009 May 13.

2Can green tea do that? A literature review of the clinical evidence. Clement Y. Prev Med. 2009. 49(2-3):83-7. Epub 2009 May 22.

3Green tea polyphenols and its constituent epigallocatechin gallate inhibits proliferation of human breast cancer cells in vitro and in vivo. Thangapazham RL, Singh AK, Sharma A, Warren J, Gaddipati JP, Maheshwari RK. Cancer. Lett. 2007. 245(1-2):232-41. Epub 2006 Mar 6.

4(-)-Epigallocatechin gallate sensitizes breast cancer cells to paclitaxel in a murine model of breast carcinoma. Ting Luo, Jiao Wang, Yancun Yin , Hui Hua, Jing Jing, Xiangming Sun, Minjing Li, You Zhang and Yangfu Jiang. Breast Cancer Research. 2010. 12(1):R8.

5 A novel prodrug of the green tea polyphenol (-)-epigallocatechin-3-gallate as a potential anticancer agent. Landis-Piwowar KR, Huo C, Chen D, Milacic V, Shi G, Chan TH, Dou QP. Cancer Res. 2007. 67(9):4303-10.

Components of Cardiovascular Disease and Green Tea

March 25th, 2010 by admin 4 comments »

An estimated 785,000 Americans had their first heart attack in 2009 and 470,000 of them are likely to have a recurrent heart attack. High cholesterol, high blood pressure, obesity, diabetes, tobacco use, and secondhand smoke are all risk factors for heart disease.

We are fortunate because enjoying between 1 and 4 cups of green tea each day is heart-healthy and has no harmful side effects for most people. Researchers estimate 3 cups of green tea each day leads to an 11% decrease in the rate of heart attack. Another study found drinking 4 cups of tea per day significantly reduced the risk of death following a heart attack.

Kenneth J. Mukamal, of the Division of General Medicine and Primary Care at Beth Israel Deaconess Medical Center and his colleagues conducted a study on the effects of tea consumption on heart attacks.2 The “Onset Study” was conducted in 45 community hospitals and tertiary care medical centers in the United States. From August 1989 to September 1994, there were 1935 patients (601 women and 1334 men) interviewed approximately 4 days after having a heart attack. It is important to note that the tea drinking level was self-reported by patients and based on their tea drinking during the past year.

Researchers found that when heart attack survivors were heavy-tea drinkers they had a 44% reduced risk of dying during the 3.5 years after their heart attacks. The reduction was based on comparison of the death rates of non-tea drinkers in the study. Moderate tea drinkers realized a 28% reduction in the risk of dying as compared to those who do not drink tea. Dr. Mukamal found the highest response to tea-drinking came from patients already living with heart disease.

Cholesterol

Green tea will help lower low density lipoprotein (LDL) cholesterol and blood pressure and control obesity and diabetes. These are all risk factors for developing heart disease. Green tea, in combination with a low fat and low cholesterol diet may reduce LDL levels by 10%. Drinking green tea will also raise high density lipoproteins (HDLs), the “good” cholesterol, in the blood and lower total cholesterol.3

Quercetin is an antioxidant in the flavonol class of molecules present in green tea. Its properties contribute to its ability to oxidize LDLs. This is significant because oxidized LDLs are critical molecules in the process that makes plaque.4 Plaque is the build-up of calcium, fats and atheromas in the arteries. This condition is commonly called “hardening of the arteries” which narrows or completely blocks the flow of blood through hardened arteries. Drinking 4 cups of tea per day improves cell quality in the lining of the heart and blood vessels and strengthens the cardiovascular system.

Inflammation

Catechins, a class of flavonols found in green tea, have been studied for their beneficial effects in the prevention of autoimmune disorders and cancer, among other maladies. Recently, catechins were found to prevent inflammation as well. Inflammation in the cardiovascular system has been identified as a contributor to heart disease. Catechins help prevent or limit cardiovascular disease by stopping processes which make molecules that act as green lights for the inflammatory process to begin.

Some scientists have concluded “catechins are potent agents for the treatment and prevention of inflammation-related cardiovascular diseases because they are critically involved in the suppression of pro-inflammatory signaling pathways.”5

1Heart Disease and Stroke Statistics—2009 Update. A Report from the American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Lloyd-Jones D, Adams R, Carnethon M, et al. Circulation. 2009.119:e21-e181.

2Tea Consumption and Mortality After Acute Myocardial Infarction. Kenneth J. Mukamal, MD, MPH, MA; Malcolm Maclure, ScD; James E. Muller, MD; Jane B. Sherwood, RN; Murray A. Mittleman, MD, Dr PH. Circulation. 2002.105:2476.

3 Heat-epimerized tea catechins rich in gallocatechin gallate and catechin gallate are more effective to inhibit cholesterol absorption than tea catechins rich in epigallocatechin gallate and epicatechin gallate. Ikeda I, Kobayashi M, Hamada T, Tsuda K, Goto H, Imaizumi K, Nozawa A, Sugimoto A, Kakuda T. 2003. J Agric Food Chem 51(25):7303–7.

4Bioavailability and health effects of dietary flavonols in man. PC Hollman and Katan, MB. Arch Toxicol Suppl. 1998. 20:237-48.

5Tea polyphenols regulate key mediators on inflammatory cardiovascular diseases.
Suzuki J, Isobe M, Morishita R, Nagai R. Mediators Inflamm. 2009:494928. Epub 2009 Jul 19.

Green Tea Health Benefits

February 13th, 2010 by admin No comments »

Antioxidants

EGCG, or epigallocatechin gallate, is what makes green tea so healthy. EGCG is just one of many, many different antioxidants. For example, you’ve probably heard of lycopene before; if nowhere else, advertised on a bottle of Heinz ketchup. Watermelon also has high concentrations of lycopene. So, green tea has antioxidants. What sorts of things can EGCG do?

Cancer

One of the major things that recent studies have revealed is that EGCG reduces carcinogenesis. In other words, it prevents cancer. This is because the antioxidants neutralize free-radicals, which cause cancer. Many different types of cancer can be helped. For example, cancers of the esophagus, lungs, prostate, stomach, and others. For more on the specifics of how antioxidants prevent cancer, take a look at the article below on antioxidants.

Oral Health

Green tea is also said to help oral health; this is because of it’s high fluoride content. Fluoride is a major ingredient in many oral health products, such as toothpaste. It can help with the remineralization of teeth by attracting calcium and other essential minerals to places where enamel has broken down. This all to say green tea helps preventing tooth decay. Some people are concerned that if one consumes too much tea, it will result in toxic levels of fluoride. This is unlikely, because the amount of fluoride contained in green tea is small enough where one would have to drink gross amounts to sustain any serious health problems. On a minor note, green tea is said to reduce bad breath. Personally I find if I drink a cup before I go to bed, I don’t have morning breath.

Immnune System

It is also said green tea can build impaired immune systems up. A compound called Theanine is present in green tea. This compound can boost the ability of ‘gamma delta T cells’ to fight infections. A ‘gamma delta T cell’ is a type of white blood cell, which is the bodies main first line of defense. By strengthening the white blood cells, Theanine is basically better equipping the infantry of the body to fight against hostile forces.

Metabolism

Another thing green tea is said to do is speed up metabolism. Some say it is good to drink green tea after a meal to help break down food more effectively. Metabolism divided into two parts; catabolism and anabolism. Catabolism is the process that creates energy, and anabolism uses energy to complete tasks such as building cells. When your body breaks down food, certain damaging chemicals are produced; things such as hydrogen peroxide. To fight this, your body has a complicated set of enzymes to detoxify these chemicals. As you may have guessed, antioxidants can help to boost this process greatly. When the antioxidants mop up these chemicals, more of the enzymes can concentrate on breaking down food for energy, thus speeding catabolism (and thus metabolism).

Relaxation

It is also said that green tea can relax and calm the nerves. This may sound a bit absurd, but it really isn’t when you look closer. Green tea contains a compound called ‘Theanine’. Like Alcohol, this compound can cross the blood-brain barrier, but unlike alcohol, it does not have an adverse affect. It can relieve both mental and physical stress, and even in repeated extremely high doses has little or no adverse affects–physical or psychological.

Other Types of Tea

So, is green tea special? Is it much better than say, black tea? Or white tea? Well, originally, green tea was considered to be much better, which is understandable. Anything ‘green’ or ‘natural’ now-a-days immediately gains for itself a healthy connotation. Black tea is oxidized completely, while green tea is for the most part not. In the tea-making community, the oxidation process is called ‘fermentation’, although technically no fermentation is taking place. This has also contributed somewhat to the negative connotation of black tea. But recent studies suggest that black and other varieties of tea are just as good as green. So, whether you drink black, white, oolong or whatever else suits your tastes, you are still reaping the benefits that green tea has recently gained the reputation of.

Green Tea Antioxidants

February 9th, 2010 by admin No comments »

Antioxidants. If you know anything about green tea and it’s health benefits, you’ve heard of antioxidants. You know that green tea can have lots of beneficial effects on your health. Much of these benefits come from the high levels of antioxidants in the tea. But what are antioxidants, and what exactly do they do? Good question.

Antioxidants are molecules, and they slow or prevent the oxidation of ‘free-radicals’ in your body. Free radicals are detrimental molecules that can cause a lot of damage to other molecules around them by stealing electrons. When one molecule steals electrons from another, this is called an oxidation reaction. Now what’s so bad about losing electrons you ask? Well, this can cause all sorts of problems, depending on the type of molecules free-radicals oxidise with.

Take oxygen. As you should know, oxygen is vital to most complex life-forms. But oxygen is also one of the most common free-radicals roaming your body. When an oxygen molecule is radicalized (when it loses electrons) it becomes positive in charge, and wants to take away electrons from other molecules around it. For example, an oxygen molecule steals electrons from a cell. This can permanently damage the cell’s DNA, and can cause a chain reaction that eventually leads to cancer. If the free-radical steals electrons from a protein, this can also cause a range of problems. ‘Enzyme Inhibition’ and ‘Protein Degredation’ are two of these problems. Enzyme Inhibition is when the free-radical embeds itself inside an enzyme; thus slowing or completely stopping the enzyme’s function. Protein Degredation is a little more complicated, but the free-radical ends up impairing immune system functionality.

So. Where do antioxidants fit into all that? Well, antioxidants react with, or ‘mop up’ the free-radicals in your body. They float around neutralizing the free-radicals by giving them electrons. By stopping the free-radicals, the antioxidants in green tea help to prevent cancer and fix impaired immune function.