Leading scientists in tea research recently held a virtual meeting at the 6th International Symposium on Tea and Health Science to discuss the current state of knowledge and gaps in understanding the benefits of tea. At the symposium, researchers discussed a number of topics, including the potential beneficial effects of tea on cardiovascular health, cognition, and cancer prevention.
The conference was organized by the Tea Council of America, the public relations arm of the tea industry, whose main goal is to encourage more tea consumption. He does this by promoting the science of tea and “claiming that tea is a healthy and wholesome drink.”
Here’s a breakdown of the main findings and an explanation of why it’s too early to draw firm conclusions.
Tea is the second most consumed beverage in the world after water. The four main types of tea include white tea, green tea, oolong tea and black tea. All four teas come from the same Camellia sinensis plant, but are processed differently after picking.
Tea contains several biologically active components, including flavonoids, L-theanine and caffeine. Many of the beneficial effects of tea are due to its richness in flavonoids, such as catechins, which have antioxidant and anti-inflammatory properties.
Differences in the production process can affect the chemical composition and beneficial effects of different types of tea. For example, green tea is roasted before it oxidizes and therefore contains more catechins. In contrast, black tea is prone to oxidation and has a lower content of catechins. Meanwhile, black tea is high in other flavonoids called thearubigins and theaflavins, which also have antioxidant properties.
Many observational studies have linked tea consumption to improved cognitive performance. Several small randomized controlled trials show that drinking tea can improve concentration in the short term.
Each cup of tea contains about 35-60 mg of caffeine, which may help improve concentration and improve mood in some people after drinking the tea. The tea also contains theanine, which some say improves concentration by reducing anxiety and stress.
Researchers believe that the presence of theanine and caffeine may induce feelings of calmness by improving concentration. In addition, limited evidence suggests that taking theanine and caffeine together may improve concentration more than taking either ingredient alone.
The flavonoids in tea may also have a protective effect against common age-related cognitive decline and dementia. Dr. Jonathan Hodgson, professor at the University of Western Australia, told Medical News Today:
“Several recent large, long-term, prospective cohort studies have examined the relationship between tea consumption and tea flavonoid intake and dementia outcomes. The two main types of dementia are Alzheimer’s disease and vascular dementia. Flavonoids are components of tea that are thought to play an important role. role in the prevention of vascular disease.
“Studies have shown that higher tea intake of just 1 to 5-6 cups [per day] is associated with a lower risk of dementia, and moderate flavonoid intake is around 2-4 cups. risk of dementia, with respect to tea and the flavonoids it contains, moderate consumption of about 2-4 cups of tea [per day] provides the greatest benefit.” — Jonathan Hodgson, Ph.D.
“In the end, these studies show that the protection offered may be strongest in vascular dementia,” he added.
A higher intake of dietary flavonoids is associated with a reduced risk of cardiovascular and metabolic diseases, including diabetes.
According to a meta-analysis combining data from 39 studies, drinking an extra cup of tea per day was associated with a 2% reduction in the risk of cardiovascular disease, a 4% reduction in the risk of stroke, and a 4% reduction in the risk of mortality due to cardiovascular disease. These positive effects of flavonoids on cardiometabolic health have been associated with reduced inflammation and oxidative stress, improved regulation of blood glucose and lipid levels, a healthier gut microbiota, and protective effects on blood vessels.
Thus, drinking tea may be especially beneficial for people whose diets lack other sources of flavonoids, including whole grains, fruits, and vegetables.
“Including two cups of unsweetened tea in your diet can be a simple and cost-effective approach to [preventing] cardiovascular disease,” said Dr. Tyler Wallace, professor in the Department of Nutrition and Nutritional Research at George Mason University.
After cardiovascular disease, cancer is the second leading cause of death. Changing lifestyle factors such as diet, physical inactivity, smoking and obesity can prevent 30-40% of cancers.
So while evidence that tea reduces cancer risk remains limited, healthier lifestyle choices can increase flavonoid levels, which may reduce cancer risk.
Commenting on the evidence, Dr. Raoul Zamora-Ros, professor at the IDIBELL Bellvitge Biomedical Research Institute, told MNT:
“There is a lot of plausible preclinical evidence that the anti-cancer properties of tea, primarily its bioactive compounds (flavonoids), prevent the onset and progression of cancer.”
“In humans, there is limited suggestive evidence that drinking tea reduces the risk of developing cancers of the biliary tract, breast, endometrium, liver, and especially oral cancer. Evidence for remaining areas of cancer remains inconclusive,” he said.
Dr. Zamora-Ros noted that larger observational studies and clinical trials are needed to further evaluate the relationship between tea consumption and cancer incidence. In addition, some studies did not distinguish between the effects of green and black tea, a deficiency that future studies should address.
Drinking tea can also improve immune health: research shows a potential role for green tea in preventing bacterial and viral infections. For example, several human studies, including randomized controlled trials, have shown that drinking green tea can reduce the risk of contracting the flu.
Dr. Dayong Wu, a professor at Tufts University in Massachusetts, said the health benefits of drinking tea for the immune system fall into two categories.
“Firstly, it is a protective effect against infection. Current research indicates that tea/tea catechins can act directly on various viruses and bacteria, preventing them from attaching and thus blocking their entry into host tissues, inhibiting their replication and limiting their spread. Tea/tea catechins can also enhance the anti-pathogenic response of the host’s immune cells, helping to fight the pathogen and eliminate infection,” he explained.
Second, the antioxidant and anti-inflammatory properties of green tea may also help prevent tissue damage caused by excessive inflammation caused by infection. Given its anti-inflammatory properties, green tea may also help relieve symptoms of autoimmune diseases such as inflammatory bowel disease and rheumatoid arthritis.
“An autoimmune disease is an immune imbalance characterized by the host’s immune cells attacking its own tissues. Tea/tea catechins have been shown to modulate complex immune cell function, thereby helping to correct this disease, possibly by suppressing hyperactive responses. and encourage tolerance,” says Dr. Wu.
However, he cautions that most of these findings are based on cell cultures and animal studies, and that more research is needed to evaluate the effects of green tea on immune function in humans.
Research discussed at the workshop links tea consumption to various health benefits. However, more research on the individual compounds in tea may be needed to iron out negative effects before dietary recommendations can be changed.
Referring to some of the key areas for future research in tea science, Dr. Joanna Dwyer, professor of medicine and senior fellow at Tufts University, said she believes “figuring out why the mystery is being maintained will be lucrative [...] some green tea supplements appear to be associated with liver toxicity, and which compounds are responsible for these effects.”
Tea has also been associated with side effects such as decreased iron absorption and increased anxiety and restlessness, due in large part to its caffeine content.
Experts point out that there are ways to get the beneficial flavonoids from decaffeinated tea, such as eating vegetables and fruits that also contain fiber.
“On a more fundamental level, it remains important to study the health-related properties of various compounds in tea,” added Dr. Dwyer.
A growing body of research is looking into the health benefits of green tea extracts, which are rich in flavonoids and other compounds.
Dr. Mario Ferruzzi, Professor and Chair of Developmental Nutrition, Department of Pediatrics, Division of Medical Sciences, University of Arkansas, spoke about the place of tea in modern nutritional guidelines.
“Currently, dietary bioactive compounds such as flavan-3-ols are not included in dietary recommendations. Polyphenols make up 30% to 40% of the solid content in a cup of green and black tea. In nutritional recommendations, phytochemicals are referred to as useful”. components of fruits and vegetables, but not drinks.
To remedy these shortcomings, Dr. Feruzzi noted that current recommendations for healthy beverages need to be expanded to include tea and coffee as sources of bioactive ingredients such as flavonoids.
In addition, nutritional advice should include appropriate intake of dietary flavonoids to ensure adequate intake of these nutrients, which may help reduce the risk of chronic disease.
Dr. Feruzzi warns that ready-to-eat foods tend to be lower in flavonoids, so consumers should prefer brewed tea over these products.
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Post time: Jan-09-2023