Many people believe that drinking more tea is good for health and helps prevent cancer, but drinking tea that is too hot can have the opposite effect.
Be careful with tea water: over 70°C can cause cancer
Iranian researchers published a study in 2009 pointing out that drinking a cup of hot tea daily can easily increase the risk of esophageal cancer. Moreover, when the tea water temperature is between 65°C and 69°C, the risk of esophageal cancer doubles. Once the water temperature exceeds 70°C, the incidence of esophageal cancer increases eightfold. If the tea is drunk within 2 minutes of pouring, the risk of developing esophageal cancer is about five times higher than if you wait 4 minutes to drink it. Another study found that when drinking tea, a temperature between 56°C and 60°C is more beneficial for health.
In addition to the risk of cancer from excessively hot tea, Zhang Silan, a nutritionist in Taiwan, reminds us that pesticide residues in tea leaves can also be harmful to health. If you are concerned about pesticide residues, you can discard the first infusion of water. When brewing tea, keep the lid off to trap the steam, allowing some pesticide substances to evaporate with the water vapor. When buying tea, try to choose organic tea for greater safety. So, what is the principle behind tea's cancer-preventing effects, and which types of cancer can be prevented by drinking tea in daily life?
I. How to drink tea to prevent cancer
1. The cancer-preventing effect of green tea
Some studies at home and abroad have shown that regardless of the type of tea, it has varying degrees of preventive and therapeutic effects on chemical carcinogenesis or metastatic tumors in experimental animals. Both endogenous and exogenous free radicals have carcinogenic effects, but natural antioxidants can scavenge free radicals. Therefore, the anti-cancer and cancer-preventing effects of these natural antioxidants have received considerable attention. Green tea is rich in natural antioxidants such as "tea polyphenols." Consumed before or after meals, various antioxidants work synergistically to scavenge free radicals, which can further enhance the cancer-preventing and anti-cancer effects of green tea.
2. "Green tea polyphenols" are an important substance in green tea's anti-cancer effect
The content of green tea polyphenols in green tea is five times that of ordinary tea. Green tea can reduce the incidence of certain cancers, but scientists were previously unclear about which substance and how it worked to prevent cancer, so they couldn't determine how much green tea a person should drink per day to be effective.
Green tea polyphenols may just be one of the substances in green tea with anti-cancer effects. They also found that the molecular structure of green tea polyphenols is similar to that of the anti-cancer drug methotrexate.
DHFR is crucial for both healthy and cancer cells. Green tea polyphenols have a strong binding affinity for DHFR, but it is weaker than that of methotrexate, so the side effects on healthy cells are smaller than those of the anti-cancer drug.
3. The cancer-preventing effect of Pu-erh tea
After comparing the effects of various green teas, it was determined that Pu-erh tea has a stronger effect in killing cancer cells. After cancer patients drink Pu-erh tea for a long period, their cancerous cells shrink from polygonal to round, their pseudopods decrease in number, they lose their ability to adhere and move, and some may even detach, float, and be lost. The remaining cells become smaller, rounder, and more concentrated, with pyknosis, condensed or disappeared chromatin, vacuoles appearing in the nucleus and cytoplasm, pyknosis or fragmentation and disappearance of the nucleolus, contraction or mutual condensation of chromosomes, a decrease in ribosomes, and expansion of mitochondria and endoplasmic reticulum. RNA synthesis decreases, and nuclear division stops. These changes demonstrate that under the pharmacological action of Pu-erh tea, cancer cells tend toward death from degeneration.
II. Which cancers can be prevented by drinking tea
1. Drinking tea to prevent prostate cancer
Recent studies show that drinking either black tea or green tea can help prevent prostate cancer, and it also helps lower cholesterol, reduce cell damage caused by smoking, and even prevent heart disease.
Foreign researchers investigated 20 male patients with prostate cancer. They drank 5 cups of green tea, black tea, etc., daily before surgery. After surgery, analysis of their blood samples and prostate tissue found that the phenol content in their tissue samples was higher. When black tea, green tea, or soda was added to the cancer cell culture medium, the growth rate of the cancer cells slowed significantly.
2. Drinking green tea is beneficial for preventing ovarian cancer
Researchers in Australia and China recently discovered through experiments that green tea can reduce the incidence of ovarian cancer in women. Women who drink green tea daily can have their incidence of ovarian cancer reduced by nearly 60% compared to other women.
To understand the causes of ovarian cancer, researchers from Curtin University in Australia and Zhejiang Cancer Hospital in China conducted an experiment on 900 women. Among them, 254 were diagnosed with ovarian cancer, and 652 were healthy women. The results showed that daily tea drinking, especially green tea, can significantly reduce the incidence of ovarian cancer in women. In addition to tea drinking, other factors such as smoking, oral contraceptives, physical exercise, and family history of ovarian cancer also have various effects on the risk of ovarian cancer.
3. Drinking green tea can prevent skin cancer
Researchers at Dartmouth Medical School in New Hampshire, USA, have recently discovered that drinking a few cups of tea daily can reduce the risk of two common types of skin cancer.
According to Reuters, the research team led by Judy Rees studied the eating habits and health of 2,200 adults and found that tea drinkers had a lower risk of developing squamous cell carcinoma and basal cell carcinoma, two common types of skin cancer. People who drank more than one cup of tea a day had a 20% to 30% lower chance of developing these two types of cancer than those who did not drink tea.
Research shows that tea contains an antioxidant called EGCG, which can limit the damage of ultraviolet radiation to the skin. This effect is more pronounced in people who have been drinking tea for decades and drink at least two cups a day.
The experts on the research team pointed out that the above findings do not mean that drinking tea can replace sun protection. There is no evidence that drinking tea can reduce the risk of skin cancer for people who get sunburned multiple times.