Tea has a long history of culture and is one of the most popular drinks. Tea not only plays an important role in social interaction, but its flavor and potential health benefits also make it popular.
However, as a daily drink, what are the health effects of tea? In recent years, many studies have discussed the benefits and risks of tea drinking from different types of tea and the effects of different diseases.
The core ingredient of health effects: tea polyphenols
Many of the health benefits of tea depend on polyphenols, such as catechins in green tea, theaflavins and thecopene in black tea. Tea polyphenols are considered to be the main components of tea color and flavor, but also have antioxidant effect.
In recent studies, tea has been shown to protect against lead and cadmium-induced oxidative stress, and tea polyphenols have been shown to improve redox imbalances and mitochondrial dysfunction in hepatocytes.
Previous studies have shown that tea polyphenols help reduce the oxidation of low-density lipoprotein cholesterol, reducing the risk of heart disease, by slowing DNA oxidation and inducing glucuronosyltransferase. Contribute to the elimination of toxins and carcinogens in the body, which may have anti-cancer effects.
In addition, tea polyphenols can promote beneficial intestinal flora and inhibit reactive oxygen species associated with aging-related diseases.
Among them, the study of cardiovascular benefits seems to be more promising.
A 2013 study in the American Journal of Clinical Nutrition found that a flavonoid in tea polyphenols helps prevent the risk of coronary artery disease and stroke; Another study points to the underlying mechanism by which these substances affect vasodilation and combat endothelial dysfunction, which is one of the etiological factors of atherosclerosis.
Are there any potential hazards?
In a large controlled study of Chinese people, a team of researchers from Fudan University and Shandong University found that drinking hot tea significantly increased the risk of esophageal squamous cell cancer in Chinese men, with a higher risk among drinkers.
But a related editorial argues that the increased risk may be due to high water temperatures, not to the tea itself. The International Agency for Research on Cancer has pointed out that drinking any overheated drink “may cause cancer.”
Most tea contains caffeine. It is estimated that black tea has the highest caffeine content, followed by oolong tea, green tea, yellow tea and white tea. But they are usually lower than the caffeine content of the same volume of coffee. If there are concerns about caffeine, the dosage is more important than the source.
The effect of tea on kidney stones is also a point of concern, but the conclusions of the relevant studies are not consistent.
In a large prospective cohort study conducted in 2018 by the School of Medicine of Shanghai Jiaotong University and Vanderbilt University Medical Center in the United States, nearly 60,000 men and 70,000 women in China were followed up and found that drinking green tea was associated with a lower risk of kidney stones. And this protective effect is more pronounced in men.
However, a 2017 study of nearly 9000 people in northern China by the Capital University of Medical Sciences and Wenzhou Medical University found that drinking tea was a risk factor for kidney stones, although the study included people who drank green tea, black tea and other teas.
The risk of nephrolithiasis is related to the concentration of calcium oxalate in urine. Some scholars pointed out that the concentration of oxalate in green tea is low, on the contrary, the concentration of oxalate in black tea is higher.
Benefits of different types of tea
In terms of common chronic diseases, a retrospective study of people in Guangzhou showed that regular and moderate consumption of green tea reduced the risk of coronary heart disease in women, but not in men. A study from Xiangya Medical College found that green tea polyphenols can prevent chronic kidney disease induced by hyperuricemia by activating the body’s function.
In cancer, catechin may reduce cancer cell activity in neuroblastoma, a common extracranial tumor in children, and inhibit both estrogen receptor-positive and estrogen-negative breast cancer cells in three different studies. Green tea polysaccharide can act on a potential target of prostate cancer and inhibit the growth of cancer cells.
In addition, studies have shown that green tea can also reduce inflammation, inhibit the growth of bacteria leading to periodontal disease, to prevent periodontal disease. Tea ammonia, an amino acid found in green tea, has also recently been shown to reduce stress.
Several studies have shown the effects of black tea on metabolic health. Low-density lipoprotein cholesterol and triglycerides decreased and high-density lipoprotein cholesterol increased significantly in rats treated with red tea polyphenols. However, a recent study published in the American Journal of Hypertension by the Jiangsu Provincial Institute of Geriatrics showed that drinking black tea in hypertensive patients was significantly associated with hyperhomocysteinemia, which can affect the risk of cardiovascular and cerebrovascular diseases. Green tea or oolong tea did not show a correlation.
In an in vitro study from Zhejiang University, a combination of tea polyphenol extract and cisplatin showed synergistic effects in cisplatin-resistant breast cancer cells. Researchers at Peking University’s School of Pharmacy have found that tea amino acids and other components extracted from black tea help to reduce aging-related neurodegenerative diseases in mice.
In a recent study at the University of St. Louis, green tea and oolong tea extracts showed DNA-damaging effects on breast cancer cells, preventing the growth and proliferation of cancer cells.
There has been a lot of evidence in recent years about the potential health benefits of drinking tea, and a number of studies have been carried out in Asian and even Chinese populations. Nevertheless, there is still a lack of definitive conclusions.
In addition, the type of tea, processing methods, drinking frequency, quantity are very different, the benefits or risks of these factors are not clear enough. More research is needed in the future to better understand the health benefits of drinking tea.
Although it is hard to say how “powerful” tea must be, at least it is sugar-free, fat-free and low-calorie, so long as it is not too hot to drink, and it is not the so-called tea drink containing all kinds of additives, just drink a few more cups.
 Drinking Tea: Are the Health Benefits Real? The Retrieved January 22, 2019, from https://www.medscape.com/viewarticle/907456
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