Researchers have recommended that people include 2-4 cups of unsweetened tea in their daily diet as a source of flavonoids, which are largely responsible for these beneficial effects.
Leading scientists in tea research recently met virtually at the Sixth International Scientific Symposium on Tea and Human Health to discuss the current state of knowledge and gaps in understanding the benefits of tea. Researchers discussed many topics at the symposium, including the potential beneficial effects of tea on cardiovascular health and cognitive function,
Here’s an analysis of the key research findings on the benefits of tea
Types of Tea and Flavonoids
Tea is the second most consumed drink in the world after water. The four main types of tea are white tea, green tea, oolong tea, and black tea. These four teas are made from the same plant, Camellia sinensis, but differ in the way they are processed after harvest. Tea contains a wide variety of components with biological activity, including flavonoids, L-theanine and caffeine. Many of the beneficial effects of tea are due to its high levels of 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 teas. For example, green tea is roasted before it oxidizes and therefore contains higher catechins. Black tea, on the other hand, can oxidize and contains fewer catechins. In addition, black tea contains higher amounts of other flavonoids called thearubigins and theaflavins, which also have antioxidant properties.
Cognitive function and cognitive decline
A number of observational studies suggest that tea consumption is associated with improvements in cognitive function. A few small randomized controlled trials have suggested that drinking tea may improve attention in the short term. Each cup of tea contains about 35-60 mg of caffeine, which may contribute to the increased alertness and mood that some people experience after consuming the tea. The tea also contains theanine, which has been suggested to improve attention while reducing anxiety and stress. Researchers believe that the presence of theanine and caffeine may be able to produce a simultaneous sense of calm while improving attention. In addition, limited evidence suggests that taking theanine and caffeine together may lead to a greater increase in attention than taking both components separately.
The flavonoids found in tea may also have protective effects against common age-related cognitive decline and dementia. Several large, long-term, prospective cohort studies have recently examined the relationships between tea consumption and consumption of flavonoids found in tea and dementia outcomes. The two main forms of dementia are Alzheimer’s disease and vascular dementia. Flavonoids are components of tea that are thought to play an important role in the prevention of vascular disease.
Other studies have found that higher tea intakes, starting at a single cup and up to 5-6 cups per day, are associated with a reduced risk of dementia. Moderate consumption of flavonoids in ~2-4 cups of tea is associated with a reduced risk of dementia, and that for both tea and the flavonoids, maximum benefit can be obtained from a moderate consumption of 2-4 cups per day.
Higher dietary intake of flavonoids is associated with a lower risk of cardiovascular disease and metabolic disorders, including diabetes. According to a meta-analysis that summarized data from 39 studies, daily consumption of each additional cup of tea was associated with a 2% lower risk of a cardiovascular event, a 4% lower risk of stroke and a 4% lower risk of death. heart and vascular disease. These positive effects of flavonoids on cardiometabolic health are associated with reduced inflammation and oxidative stress, better regulation of blood sugar and lipid levels, healthier gut microbiome and protective effects on blood vessels. Thus, tea consumption may be particularly beneficial for people whose diets are deficient in flavonoids, including whole grains, fruits and vegetables.
Tea and immune function
Drinking tea may also improve immune system health, with studies suggesting a possible role for green tea in preventing bacterial and viral infections. For example, a number of studies in humans, including randomized controlled trials, suggest that drinking green tea may reduce the risk of the incidence of influenza infection.
Immune System: Two Categories of Benefits
The first is the protective effect against infection. Current research shows that tea/tea catechins can act directly on a variety of viruses and bacteria to prevent them from attaching and thereby blocking their access to host tissues, inhibiting their replication and limiting their spread. Tea/tea catechins can also enhance the antipathogenic response of the host immune cells to fight pathogens and eliminate infections,” he explains.
Second, green tea’s antioxidant and anti-inflammatory properties may also help prevent tissue damage caused by excessive inflammation in response to infection. Given its anti-inflammatory properties, green tea may also help relieve symptoms of autoimmune disorders, such as inflammatory bowel disease and rheumatoid arthritis.
Autoimmune disease represents an immune imbalance and is characterized by a host’s immune cells attacking its own tissues. Tea/tea catechins have been shown to modulate complex immune cell function in ways that help correct this condition, perhaps by suppressing the overactive response and promoting tolerance. However, most of these findings are based on cell cultures and animal studies, and further studies are needed to assess the impact of green tea on immune function in humans.
Beneficial properties of green tea catechins
Exploring the potential of black tea-based flavonoids against hyperlipidemia-related disorders
Drinking tea: a systematic review of randomized controlled trials focusing on human cognition, mental wellbeing and brain function
Dose-response relationship between tea consumption and risk of cardiovascular disease and all-cause mortality: a systematic review and meta-analysis of population-based studies
Anti-flu with green tea catechins: a systematic review and meta-analysis