There are several studies that attribute many healthful properties to tea. Let us explore the relationship between tea drinking and cancer, or heart disease.
Can tea prevent cancer?
The short answer to the question in the title is: no. But there are many studies that give weight to the belief that it certainly helps.
Lung, prostate, breast, bladder and other cancers have all been the subject of intense research over the past 50 years. All of them have been favorably influenced by compounds commonly found in tea.
One of the most promising of recent finds is the identification of an antioxidant called EGCG (epigallocatechin gallate).
Antioxidants have long been believed to help hinder or slow the growth of cancer cells and tumors. U.S. National Cancer Institute studies have shown that catechins, a component of tea, inactivate oxidants, reducing the number and size of tumors.
EGCG may be one of the reasons.
Patients in a recent Japanese study at Kyushu University drank two to three cups of green tea per day, rich in EGCG. The researchers found that human lung cancer cells grew more slowly when they did. In test tube studies, EGCG inhibited an enzyme that cancer cells require in order to grow and divide.
A Spanish/British co-study reinforces the idea. Researchers at the University of Murcia and the John Innes Center in England found that EGCG in green tea prevented cancer cells from growing large enough to divide. The mechanism is believed to be the result of EGCG's ability to bind to the specific enzyme (dihydrofolate reductase) needed.
USC (University of Southern California) researchers studying breast cancer found similar results. Green tea drinkers had a lower incidence of tumors, even adjusting for other factors such as family history, exercise and diet. Here, one important factor appears to be the ability of certain compounds in tea to inhibit the growth of blood vessels.
Cancer cells, just like any other, need nutrients from blood in order to grow. They stimulate the growth of blood vessels in order to supply themselves. Tea inhibits that ability, according to a joint study by the University of California and the University of Texas.
Other studies show that drinking five cups per day can help boost the immune system, providing the body with an ability to combat emerging cancer cells. Alkylamine antigens are thought to be responsible. Ingesting them by drinking tea produces a more vigorous response against tumors.
Another study examined bladder cancer. An extract made from green tea altered the actions of actin, a structural protein needed by cancer cells to function. A process called 'remodeling' allows cancer cells to invade nearby healthy tissue. A compound made from green tea modified the cancer cell's ability to carry out this process.
While the specific mechanisms are still a matter of ongoing research, a cluster of studies all point to tea's ability to assist in preventing cancers. There are no known downsides to consuming a few cups per day, either. It's a smart choice.
Can tea drinking prevent heart disease?
The short answer to the question posed in the title is: no. But there are numerous studies that lend credence to a popular idea that tea can help improve heart health.
Tea contains a type of polyphenol compound called catechins. Many teas undergo oxidation of catechins, producing theaflavins. Which, and how much, of each type of compound varies between types of tea.
White teas undergo the least processing, typically being protected from oxidation. The buds are harvested young and they don't go through the drying process that causes other teas to darken. That leaves all the original catechins intact. Green teas undergo slight oxidation and black teas get the most. But each type still has heart health benefits, despite the differing concentrations and forms of polyphenols.
In one six year Dutch study of almost 5,000 men and women, those who drank a little more than a cup and a half per day had a risk of heart attack only two-thirds that of non-tea drinkers. A Japanese study followed over 8,500 men and women for 12 years. It found those who drank at least four cups of green tea per day had about half the risk of coronary disease of non-tea drinkers.
Tea is known to help reduce the formation of the harmful form of cholesterol, LDL. The flavonoids in tea prevent it from oxidizing. That adds to the beneficial effects by decreasing the risk of hardening of the arteries.
It isn't only green tea which has heart health benefits, though.
Heart attack and blood pressure are closely related. Higher blood pressure increases the risk of heart attack, as well as contributing to other health problems.
Black tea consumption helps reduce blood pressure by reducing the risk of atherosclerosis, which interferes with the ability of blood vessels to relax. Blood pressure measurements in one study were lower among tea drinkers. The risk of hypertension (high blood pressure) were cut in half by consuming just one cup per day. For those who consumed three cups per day, the risk was lowered by two-thirds.
Myocardial infarction is one common form of heart attack. A Harvard study done ten years ago found that a single cup of black tea per day lowered Myocardial infarction risk by 44%, compared to non-tea drinkers.