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The L-theanine molecule present in tea decreases heart rate and reduces stress without inducing sleepiness.
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Taylor Wallace, Ph.D., principal and CEO at the Think Healthy Group and a professor in the Department of Nutrition and Food Studies at George Mason University, U.S.
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Jonathan Hodgson, Ph.D., professor at the Institute for Nutrition Research at Edith Cowan University, Australia.
During the Sixth International Symposium on Tea and Human Health, experts explored evidence on the cognitive and cardiovascular benefits of consuming tea.
In April, experts in a variety of disciplines convened for the Sixth International Symposium on Tea and Human Health. During the virtual event, cognitive and cardiovascular benefits of tea consumption emerged as key themes. Three symposium speakers followed up with STiR Coffee and Tea Magazine to share their insights into the findings on the benefits of drinking tea.
Short-term cognitive benefits
Louise Dye, Ph.D., professor of nutrition and behavior at the University of Leeds, U.K., spoke about how tea and its components, including caffeine and L-theanine, have the potential to positively impact attention during periods of stress. Researchers explored how the amino acid L-theanine present in tea impacts alertness. One study found that L-theanine reduces both physiological and psychological stress responses. When given an arithmetic problem, study participants who consumed L-theanine demonstrated responses such as decreased heart rate compared to the study’s placebo group.
Another study measured alpha activity, which plays a role in attention, in the brain via EEG. Researchers concluded that dietary levels of L-theanine help to relax the brain without contributing to drowsiness. While research like this is promising, Dr. Dye hopes to see more studies supporting the positive relationship between tea and short-term cognition.
“The potentially beneficial effects of tea and tea components on attention especially under conditions of stress require further validation in different samples and using different stressors, e.g., induced versus real-life,” said Dr. Dye.
Long-term cognitive benefits
While drinking tea might help people to focus during a task at-hand, what kind of cognitive effects does tea consumption have over time? During the symposium, Jonathan Hodgson, Ph.D., professor at the Institute for Nutrition Research at Australia's Edith Cowan University, spoke about the potential for tea consumption to reduce the risk of dementia. “The past three years has seen publication of several high-quality studies, which indicate that easily achievable tea intakes and intakes of the flavonoids found in tea could reduce dementia risk,” he said.
A single cup of tea (200 milliliters) is rich in a multitude of flavonoids, including catechins, flavonols, flavones, thearubigins, and theaflavins, according to a study published in QJM: An International Journal of Medicine.
Dr. Hodgson points to a number of studies that support the positive link between flavonoid intake and decreased risk for cognitive decline. Flavonoids are the subject of a number of studies exploring their correlation with dementia, stroke, and cognitive decline. One study that followed nearly 50,000 men and women in the United States concluded that higher flavonoid intake is associated with a lower risk of subjective cognitive decline. Other studies have demonstrated a promising link between flavonoid intake and decreased risk of Alzheimer’s disease and related dementias, as well as a lower risk of stroke and dementia.
“Because the evidence is almost entirely from observational studies, we cannot infer causality,” says Dr. Hodgson. “However, we can say that tea is a healthy beverage that is likely to provide benefits to the health of your blood vessels. The associations with dementia, and particularly vascular dementia, are consistent with this evidence. Ideally, I would like to see large long-term randomized controlled trials investigating the causal effects of flavonoid-rich foods and beverages such as tea.”
Cardiovascular benefits
Tea may be good for the heart as well as the head. Taylor Wallace, Ph.D., principal and CEO at the Think Healthy Group and a professor in the Department of Nutrition and Food Studies at George Mason University, U.S., examined the cardiovascular benefits of consuming black and green tea. “I think the most exciting aspect is how consistent the data is across all research designs. It all points to [approximately] two cups of unsweetened tea per day for cardiovascular health,” he explained.
Tea may not impact cardiovascular health immediately, according to one study. Researchers concluded that short-term consumption (4 to 24 weeks) does not have a notable effect on blood pressure or blood lipids. The study concluded that more randomized controlled trials of a longer duration were needed to further explore the relationship between tea drinking and decreased cardiovascular disease.
Another study that involved a systematic review and metanalysis of population-based studies found a moderate level of evidence to support the relationship between tea consumption and a decreased risk of mortality related to cardiovascular disease. The study found no adverse effects associated with drinking tea in regular amounts.
Dr. Wallace conducted an umbrella review to evaluate the available evidence of the relationship between tea and the decreased risk of cardiovascular disease and cardiovascular disease progression. A total of 23 systematic reviews revealed a significant potential for decreased cardiovascular disease and cardiovascular events, such as stroke, due to the flavonoids present in tea. Research indicates the potential for flavonoids to decrease LDL cholesterol, systolic blood pressure, and diastolic blood pressure. It is also possible that tea flavonoids have a positive impact on inflammation markers, but more research is needed.
The argument for tea intake
While more research remains to be done to understand and validate the health benefits of drinking tea, several experts who spoke at the symposium believe that the wealth of evidence available today could be used to support current dietary guidelines. Incorporating tea into the diet is simple, and it does not come with significant risk. Tea consumption holds the promise of significant health benefits, and more research could further illuminate exactly how tea and its components lead to cognitive and cardiovascular benefits and more.
“I think the Dietary Guidelines Advisory Committee should begin to incorporate data on bioactives like flavonoids present in tea into their recommendations,” said Dr. Wallace. “Currently, the guidelines are based on meeting essential nutrient requirements only. The Academy of Nutrition and Dietetics should be involved in helping reach consumers.” The Dietary Guidelines Advisory Committee is a U.S. federal government group, while the Academy is a trade association based in Chicago, Illinois, U.S.