What you don’t know about green tea

Over centuries, tea has been cultivated, beginning in India and China. Today, tea is the most widely consumed beverage in the globe, second only to water. Hundreds of millions of people drink tea, and studies suggest that green tea (Camellia sinesis) in particular has many health benefits.

Made from unfermented leaves, green tea reportedly contains the highest concentration of powerful antioxidants called polyphenols. Antioxidants are substances that fight free radicals – damaging compounds in the body that change cells, damage deoxyribonucleic acid (DNA), and even cause cell death.

Many scientists believe that free radicals contribute to the ageing process as well as the development of a number of health problems, including cancer and heart disease. Antioxidants such as polyphenols in green tea can neutralise free radicals and may reduce or even help prevent some of the damage they cause.

In traditional Chinese and Indian medicine, practitioners used green tea as a stimulant, a diuretic (to help rid the body of excess fluid), an astringent (to control bleeding and help heal wounds), and to improve heart health. Other traditional uses of green tea include treating gas, regulating body temperature and blood sugar, promoting digestion, and improving mental processes.

Green tea has been extensively studied in people, animals, and laboratory experiments. Results from clinical studies suggest that its antioxidant properties may help prevent atherosclerosis, particularly coronary artery disease.

Though researchers are not sure why green tea reduces the risk of heart disease by lowering cholesterol and triglyceride levels, studies show that black tea has similar effects. In fact, researchers estimate that the rate of heart attack decreases by 11 percent with consumption of three cups of tea per day.

High cholesterol

Research shows that green tea lowers total cholesterol and raises HDL (“good”) cholesterol in both animals and people. One population-based clinical study found that men who drink green tea are more likely to have lower total cholesterol than those who do not drink green tea.

Results from one animal study suggest that polyphenols in green tea may block cholesterol from being absorbed in the intestine and also help the body get rid of cholesterol. In another small study of male smokers, researchers found that green tea significantly reduced blood levels of harmful LDL cholesterol.

Cancer

Several population-based clinical studies have shown that both green and black teas may help protect against cancer. For example, 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 population-based 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.

Breast cancer

Clinical 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 pre-menopausal women in the early stages of breast cancer. They also found that women with early stages of the disease who drank at least five cups of tea every day before being diagnosed with cancer were less likely to have the cancer come back 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 three or more cups of tea per day were 37 percent less likely to develop breast cancer compared with women who didn’t drink tea.

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 even these studies have been conflicting.

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 clinical 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.

Prostate cancer

Laboratory studies have found that green tea extracts prevent the growth of prostate cancer cells in test tubes. In a large clinical study in Southeast China, researchers 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.

Diabetes

Green tea has been used traditionally to control blood sugar levels. Animal studies suggest that green tea may help prevent the development of type 1 diabetes and slow the progression once it has developed. In people with type 1 diabetes, their bodies make little or no insulin, which helps convert glucose or sugar into energy. Green tea may help regulate glucose in the body.

A few small clinical studies have found that taking a green tea extract daily lowered the haemoglobin A1c level in people with borderline diabetes.

Weight loss

Clinical studies suggest that green tea extract may boost metabolism and help burn fat. One study found that the combination of green tea and caffeine improved weight loss and maintenance in people who were overweight and moderately obese. Some researchers think that substances in green tea known as catechins are responsible for the herb’s fat-burning effect.

What is it made of?

Researchers think the health-giving properties of green tea are mostly due to polyphenols, chemicals with potent antioxidant properties. 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 flavour.

Polyphenols contained in teas are classified as catechins. Green tea contains six primary catechin compounds: catechin, gallaogatechin, epicatechin, epigallocatechin, epicatechin gallate, and apigallocatechin 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.

Anne Agbaje