Several population-based studies suggest that both
green and black teas help protect against cancer
Cancer rates tend to be low in countries such as Japan where people regularly consume green tea. However, it is not possible to know for sure from these studies whether green tea actually prevents cancer in people. Early clinical studies suggest that the polyphenols in tea, especially green tea, may play an important role in the prevention of cancer. Researchers also believe that polyphenols help kill cancerous cells and stop them from growing.
What's Tea Made Of?
Researchers think the health properties of green tea are mostly due to polyphenols, chemicals with potent antioxidant potential. In fact, the antioxidant effects of polyphenols seem to be greater than vitamin C. The polyphenols in green tea also give it a somewhat bitter flavor.
Polyphenols contained in teas are classified as catechins. Green tea contains six primary catechin compounds: catechin, gallocatechin, epicatechin, epigallocatechin, epicatechin gallate, and epigallocatechin gallate (also known as EGCG). EGCG is the most studied polyphenol component in green tea and the most active.
Green tea also contains alkaloids including caffeine, theobromine, and theophylline. They provide green tea's stimulant effects. L-theanine, an amino acid compound found in green tea, has been studied for its calming effects on the nervous system.
Tea's Affect on Various Types of Cancer
Bladder cancer. In one study that compared people with and without bladder cancer, researchers found that women who drank black tea and powdered green tea were less likely to develop bladder cancer. A follow-up clinical study by the same group of researchers revealed that people with bladder cancer, particularly men, who drank green tea had a better 5-year survival rate than those who did not drink green tea. People with cancer should consult with their doctor before adding tea to their regimen.
Breast cancer. Studies in animals and test tubes suggest that polyphenols in green tea inhibit the growth of breast cancer cells. In one study of 472 women with various stages of breast cancer, researchers found that women who drank the most green tea had the least spread of cancer. It was especially true in premenopausal women in the early stages of breast cancer. They also found that women with early stages of the disease who drank at least 5 cups of tea daily before being diagnosed with cancer were less likely to experience a recurrence after they finished treatment. However, women with late stages of breast cancer had little or no improvement from drinking green tea.
There is no clear evidence one way or the other about green tea and breast cancer prevention. In one very large study, researchers found that drinking tea, green or any other type, was not associated with a reduced risk of breast cancer. However, when the researchers broke down the sample by age, they found that women under the age of 50 who consumed 3 or more cups of tea per day were 37% less likely to develop breast cancer compared to women who did not drink tea.
Ovarian cancer. In a study done with ovarian cancer patients in China, researchers found that women who drank at least one cup of green tea per day lived longer with the disease than those who did not drink green tea. In fact, those who drank the most tea, lived the longest. But other studies found no beneficial effects.
Colorectal cancer. Studies on the effects of green tea on colon or rectal cancer have shown conflicting results. Some studies show decreased risk in those who drink the tea, while others show increased risk. In one study, women who drank 5 or more cups of green tea per day had a lower risk of colorectal cancer compared to non-tea drinkers. However, there was no protective effect for men. Other studies show that drinking tea regularly may reduce the risk of colorectal cancer in women. More research is needed before researchers can recommend green tea for the prevention of colorectal cancer.
Esophageal cancer. Studies in laboratory animals have found that green tea polyphenols inhibit the growth of esophageal cancer cells. However, studies on people have produced conflicting findings. For example, one large-scale population-based study found that green tea offered protection against the development of esophageal cancer, particularly among women. Another population-based study found just the opposite, green tea consumption was associated with an increased risk of esophageal cancer. In fact, the stronger and hotter the tea, the greater the risk. Given these conflicting results, more research is needed before scientists can recommend green tea for the prevention of esophageal cancer.
Lung cancer. While green tea polyphenols have been shown to inhibit the growth of human lung cancer cells in test tubes, few clinical studies have looked at the link between drinking green tea and lung cancer in people, and the studies that have been done show conflicting results. One population-based study found that Okinawan tea, similar to green tea but partially fermented, was associated with lower lung cancer risk, particularly among women. But a second study found that green tea and black tea increased the risk of lung cancer. More studies are needed before researchers can draw any conclusions about green tea and lung cancer. Green tea should not be used by patients on bortezomib therapy.
Pancreatic cancer. In one large-scale clinical study, researchers compared green tea drinkers with nondrinkers and found that those who drank the most tea were less likely to develop pancreatic cancer. This was particularly true for women, those who drank the most green tea were half as likely to develop pancreatic cancer as those who drank less tea. Men who drank the most tea were 37% less likely to develop pancreatic cancer.
However, it is not clear from this population-based study whether green tea is solely responsible for lowering pancreatic cancer risk. More studies are needed before researchers can recommend green tea for the prevention of pancreatic cancer.
Prostate cancer. Laboratory studies have found that green tea extracts prevent the growth of prostate cancer cells in test tubes. A large clinical study in Southeast China found that the risk of prostate cancer went down with increasing frequency, duration, and quantity of green tea consumption. However, both green and black tea extracts also stimulated genes that cause cells to be less sensitive to chemotherapy drugs. People who are undergoing chemotherapy should ask their doctors before drinking green or black tea or taking tea supplements.
Skin cancer. The main polyphenol in green tea is epigallocatechin gallate (EGCG). Scientific studies suggest that EGCG and green tea polyphenols have anti-inflammatory and anticancer properties that may help prevent the development and growth of skin tumors.
Stomach cancer. Laboratory studies have found that green tea polyphenols inhibit the growth of stomach cancer cells in test tubes, however, studies in people have been less conclusive. In two studies that compared green tea drinkers with non-drinkers, researchers found that people who drank tea were about half as likely to develop stomach cancer and stomach inflammation as those who did not drink green tea. However, a clinical study with more than 26,000 men and women in Japan found no association between green tea and stomach cancer risk. Some studies even suggest that green tea may increase the risk of stomach cancer.
More studies are underway to see whether green tea helps reduce the risk of stomach cancer.
Reference: To read the complete article go to https://www.mountsinai.org/health-library/herb/green-tea, Green Tea, Mt. Sinai Health Library. Sourced: 03/28/2023.