Leading nutrition scientists from around the world convened yesterday to present the latest evidence supporting the role of tea in promoting optimal health. With new findings from the international scientific community consistently lending credibility to tea’s healthy properties, speakers at the symposium provided a comprehensive update of recent research on the benefits of tea consumption on human health. As the second most consumed beverage in the world next to water, over 159 million Americans are drinking tea on any given day.
“There is a growing body of research from around the world demonstrating that drinking tea can enhance human health in many ways,” said symposium chair, Jeffrey Blumberg, PhD, an active Professor Emeritus in the Friedman School of Nutrition Science and Policy at Tufts University. “True teas – which include black, green, white, oolong, and dark – can contribute significantly to the promotion of public health. Evidence presented at this symposium reveals results - ranging from suggestive to compelling - about the benefits of tea on cancer, cardiometabolic disease, cognitive performance, and immune function.”
The chemistry in your cup
Tea contains flavonoids, naturally occurring compounds that have antioxidant properties. Tea flavonoids provide bioactive compounds that help to neutralize free radicals which may damage elements in the body, such as genetic material and lipids, and contribute to chronic disease. Tea also contains L-theanine, an amino acid that is for the most part, uniquely found in tea.
Tea and immune function
“Tea may help support your immune system and increase your body’s resistance to illnesses,” says Dayong Wu, MD, PhD, Nutritional Immunology Laboratory in the USDA Jean Mayer Human Nutrition Research Center on Aging at Tufts University. “In the event you do become sick, tea can help your body respond to illness in a more efficient way by ridding itself of the infection and may also alleviate its severity when they happen.”
In a comprehensive review of the published data on this topic presented at the symposium, Wu concluded that green tea/catechins have been shown to help the host fight against a variety of pathogens by decreasing the pathogen's ability to infect the host and helping the host's immune system spring into action. Green tea/catechins have also been shown to improve autoimmune disorders by promoting self-tolerance, suppressing autoantigen-induced inflammatory attack, and enhancing tissue repair.
Tea and cognitive function
When it comes to cognitive function, it turns out tea may offer significant benefits. “There is strong evidence that tea and its constituents seem to be beneficial under conditions of stress. The most profound cognitive domain that tea seems to act upon is attention and alertness,” explains Louise Dye, PhD, Professor of Nutrition and Behaviour at the University of Leeds. “With these effects on attention, tea is an optimal beverage of choice during a time of elevated stress and burnout worldwide.”
In her review of published research on this subject, Dye revealed that evidence from randomized controlled trials supports the conclusion that tea consumption can produce short term acute beneficial effects on attention measured by objective tests such as the attention switching test and on subjective reports of alertness. Studies consistently show beneficial effects of a high dose of L-theanine, together with a lower dose of caffeine, on attention task performance. These findings indicate that the unique combination of caffeine and L-theanine that is found in tea can improve attention.
Tea and the prevention of cognitive decline
With no effective drug treatments for dementia, prevention is key. It is estimated that 40 to 50% of dementia could be prevented through changes in lifestyle factors. In a review of published research on tea and cognitive decline, Jonathan Hodgson, PhD, Professor at the Institute for Nutrition Research at Edith Cowan University, explains that “there is growing evidence that as little as 1 to 2 cups of tea daily could significantly reduce risk of vascular dementia and potentially Alzheimer’s disease.”
Recent high-quality data from long-term, prospective cohort studies indicate that higher intakes of tea – starting at as little as 1 cup daily and up to 5 to 6 daily – are associated with reduced risk for dementia. Data from these studies also find that moderate intakes of the flavonoids present in tea are associated with reduced risk for cognitive decline. Maximal benefits of tea may be obtained from as little as 2 to 4 cups per day, with little additional benefits with higher intakes. Results of these studies also suggest that the protection provided may be strongest for protection against vascular dementia, one of the most common forms of dementia.
Tea and cancer prevention
In examining existing data on tea and cancer prevention, higher intakes of tea consumptions may reduce the risk of some cancers. There is evidence that tea flavonoids may act via antioxidant, anti-angiogenesis, and anti-inflammatory mechanisms as well modifying the profile of gut microbiota. Tea is a beverage rich in flavonoids, which are bioactive compounds with several anticarcinogenic properties in experimental studies. Suggestive evidence indicates tea consumption may reduce risk of biliary tract, breast, endometrial, liver, and oral cancer.
“While more research needs to be done to determine the exact dosage, the conclusion we can share is that higher intakes of tea consumptions may reduce the risk of some forms of cancer,” says Raul Zamora-Ros, PhD, Principal Investigator at the Unit of Nutrition and Cancer at IDIBELL.
Tea and cardiovascular health
Cardiometabolic diseases, like diabetes and heart disease, are the number one cause of death worldwide, and tea consumption may be inversely associated with adverse cardiometabolic outcomes, according to results from population studies. Based on an extensive and variety of scientific research designs, 2-cups of unsweet tea per day has the potential to mitigate cardiometabolic disease risk and progression in adults.
In an extensive review on cardiovascular health and tea, research demonstrated each cup of daily tea consumption was associated with an average 1.5% lower risk of all-cause mortality, 4% lower risk of cardiovascular disease (CVD) mortality, 2% lower risk of CVD events, and 4% lower risk of stoke events. “When you look at all the different biomarkers and mechanisms that tea is affecting, this bountiful beverage is one which consumers can easily add to better their diet and create a healthier and longer life for themselves,” explains Taylor Wallace, PhD, Principle and CEO at the Think Healthy Group and a Professor in the Department of Nutrition and Food Studies at George Mason University.
Tea and dietary guidance
To support the growing evidence of tea as a health promoting beverage, clearer recommendations are needed in the current US dietary guidance. “There may be other herbals and botanical products that can deliver health benefits, but none of them are as systematically studied as Camellia sinensis – true tea,” says Mario Feruzzi, PhD, Professor and Chief of the Section of Developmental Nutrition in the Department of Pediatrics at the University of Arkansas for Medical Sciences. “With true teas – white, green, black and oolong - you’re dealing with thousands of years of traditional use, 60-70 years of systematic study which, in the last 15-20 years, has ramped up to the point where we have very definitive data.”
Dietary guidance will provide more accurate and relevant direction for consumers in the context of the diversity of tea and other flavonoid containing foods.