Green tea is known to reduce cholesterol levels, burn fat, prevent diabetes, prevent stroke, and control dementia. It is also known to have the potential to fight cancer and heart disease. Most of these beliefs are quite intriguing as there are very limited studies to prove the benefits. Katherine Tallmadge, RD, LD, a nutritionist and spokeswoman for the American Dietetic Association, believes in the potential of green tea in improving health in different ways.
Experts say that most of the evidence collected till today comes from the lab and real world evidence is missing until now. Few clinical studies that focused on the effect of green tea on heart disease and cancer have given promising results. Most of these studies were conducted in the East where green tea is an important part of the diet. “The results of the study are naturally influenced by the lifestyle factors like high intake of fish and soy protein," feels Nieca Goldberg, MD, a spokeswoman for the American Heart Association and medical director of the New York University Women's Heart Center. In spite of this, she agrees that green tea has a number of antioxidants, which helps to maintain good health.
Green Tea and Antioxidants
Catechins, the most abundant antioxidant in green tea, scavenge for free radicals that are the most important cause of cancer, blood clots and atherosclerosis. Green tea has very minimal processing as it includes only withering and steaming, unlike the black and oolong tea where they are fermented. Thus, the catechins of green tea, especially epigallocatechin-3-gallate (EGCG), are concentrated. “The bioavailability of these antioxidants is poor and this must be overcome to get the maximum health benefits from green tea," says Tak-Hang Chan, PhD, professor emeritus in the department of chemistry at McGill University in Montreal.
Green Tea and Cancer
Some of the lab studies had shown very promising results that EGCG regulates and inhibits the growth of cancer cells and kill the tumor cells. But clinical studies have not shown the same results in human beings, remarks Marji McCullough, ScD, RD, the American Cancer Society's strategic director of nutritional epidemiology. One of the major challenges of conducting a clinical study is to find a population which drinks enough green tea and had been having it for a long time, she says. Long exposure time is very important in case of cancer.
There are few studies which show that drinking at least two glasses of green tea in a day inhibits the growth of cancer cells. In a study conducted in Japan on 500 women with Stage I or Stage II breast cancer, consumption of green tea before and after the surgery was found to reduce the chances of recurrence of cancer. Another study in China showed that more the intake of green tea, lower the risk of cancers like esophageal cancer, prostate cancer, colorectal cancer and pancreatic cancer. A recent review of studies related to the correlation of green tea intake and reduced risk of lung cancer show that an increase in the daily consumption of green tea by two cups reduces the risk of lung cancer by 18%.
Green Tea and Heart
Some studies show a clear correlation between green tea consumption and healthy heart, while some studies give contradictory results with this regard. In a study conducted in 500 Japanese men, an intake of four cups of green tea per day decreases the severity of coronary heart diseases. Another study conducted by Dutch researchers shows that more the intake of green tea, lower the severity of clogging of blood vessels in the heart. Lifestyle plays a major role in the shaping of results in these studies, says Goldberg. But she does agree that the antioxidants present in green tea act as dilators preventing the clogging of blood vessel.
Goldberg feels that people should know about these studies as they show that everyday foods have health benefits. Although heart-health benefits of green tea are known, doctors rarely recommend green tea to people. There is no evidence to the heart benefits of green tea as compared to the benefits of exercise in improving the health of the heart.
Green Tea and Healthy Weight
Green tea has been shown to have the potential to fight obesity and lower the levels of cholesterol. These are two major risk factors for heart disease and diabetes. There are two studies — one conducted in the Netherlands and the other in Japan — that have showcased these benefits. In the study, conducted by Dutch researchers, participants who drank caffeinated green tea lost more weight. The results show that even those people who drank the decaffeinated variety showed a decrease in the body weight. In the study, conducted by Japanese researchers, 240 participants were given different amounts of green tea extract for almost three months. Results show that those participants who got the highest amount of green tea lost both fat and weight, and also had low blood pressure and low levels of LDL cholesterol.
Weight loss supplements containing extracts of green tea also may be helpful, unless there are any liver disorders. But the best way to get maximum benefits from green tea is to drink it. “When all the studies are considered, it shows that taking green tea everyday will definitely affect the health," says Diane McKay, PhD, a Tufts University scientist who studies antioxidants. It cannot be taken as a drug but it can complement the diet. Experts suggest that eat fruits, vegetables, grains, seeds, and nuts and also have few cups of green tea. It is not that supplements won’t help, it is just that as there are many compounds in green tea, and many of them would have to be consumed together.