Nutrition What every dentist should know about tea Moshe M. Rechthand n Judith A. Porter, DDS, EdD, FICD n Nasir Bashirelahi, PhD Tea is one of the most frequently consumed beverages in the world, of drinking tea, as well as the potential negative aspects of tea second only to water. Repeated media coverage about the positive consumption. health benefits of tea has renewed interest in the beverage, particularly Received: August 23, 2013 among Americans. This article reviews the general and specific benefits Accepted: October 1, 2013 ea has been a staple of Chinese life for their original form.4 Epigallocatechin-3- known as reactive oxygen species (ROS) so long that it is considered to be 1 of galate (EGCG) is the principal bioactive are formed through normal aerobic cellular Tthe 7 necessities of Chinese culture.1 catechin left intact in green tea and the metabolism. During this process, oxygen is The popularity of tea should come as no one responsible for many of its health partially reduced to form a reactive radical surprise considering the recent studies benefits.3 By contrast, black tea is fully as a byproduct in the formation of water. conducted confirming tea’s remarkable oxidized/fermented during processing, ROS are helpful to the body because they health benefits.2,3 The drinking of tea dates which accounts for both its stronger flavor assist in the degradation of microbial back to the third millenium BCE, when and the fact that its catechin content is disease.5 However, ROS also contain free Shen Nong, the famous Chinese emperor lower than the other teas.2 Black tea’s fer- radical electrons that can wreak havoc on and herbalist, discovered the special brew. mentation process is initiated by withering the body’s normal functions.5,6 The list According to legend, the emperor was the leaves for up to 18 hours.1 Next, the of disorders with a positive correlation boiling water when leaves from a wild tea leaves are machine-rolled to break up the to ROS includes cancer, autoimmune bush accidentally fell into his simmer- plant cells (in order to hasten the oxida- disorders, heart disease, gastrointestinal ing pot. Since then, tea has been used in tion process); at that point, the leaves are disease, cataracts, Alzheimer’s disease, and Chinese culture for medicinal purposes, incubated in a climate-controlled room Parkinson’s disease.6 ROS and free radicals religious practices, and personal enjoy- where the oxidation process is completed.1 may be the most significant contributors ment.1 In time, tea spread in popularity, Polyphenol oxidase, the enzyme respon- to the aging process of the human body.5 and as of 2011, Great Britain had the sible for oxidation, converts the original Antioxidants—such as the catechins highest tea consumption in the world.1 polyphenols into other compounds such found in tea—are electron donors, mean- as theaflavins, theaflagallins, and thearubi- ing that they contain free electrons that Varieties of tea gens.4 The degree of fermentation can be can be paired with the damaging single All true teas are derived from the leaves of carefully controlled to create many differ- electrons found in ROS.6 This pairing the Camellia sinensis plant, which is indig- ent varieties of tea. Oolong tea is partially reduces the tendency of free radicals enous to China.2 Much of the medicinal oxidized (somewhere between green and to pair with electrons found in healthy properties of tea have been attributed to black tea) and undergoes what may be body tissues, preventing a chain reaction its antioxidant content, specifically the the most difficult and time-consuming of damaging effects. class of flavonoids/polyphenols called cat- method of processing.2 The oolong echins.3 The 4 main varieties of tea (green, process is tightly controlled and includes Cardiovascular benefits black, oolong, and white) all undergo shaking and drying the leaves in bamboo The endothelial cells of the body that line similar processing and manufacturing. The baskets to bruise the edges lightly.1 the circulatory system and maintain per- main difference between these teas is their Shortly after, the leaves undergo a short meability produce nitric oxide, a substance polyphenolic content, which depends on fermentation period and then a firing pro- that helps protect the cells by acting on the degree of oxidation or fermentation cess to prevent further oxidation.1 While the vascular smooth muscle to relax blood that the leaves undergo.2 Green tea is non- green tea might be better known for its vessels. Nitric oxide has been indicated fermented and contains a higher catechin health benefits, white tea might actually as an anti-atherosclerotic agent, prevent- concentration than most teas. This is due offer more.1 White teas are made from ing pathologic hardening of the blood to the inactivation of the polyphenol oxi- young leaves and immature buds and vessel walls. Catechins found in tea have dase present in the tea, which is an impor- undergo no fermentation or processing at a similar effect on the blood vessels by tant catalyst in the oxidation reaction that all, which allows them to retain the high- promoting vasodilation.7 In addition, the occurs during processing.3 When green est possible concentration of cathechins.2 antioxidants in tea help prevent oxidant tea is manufactured, its leaves are withered injury when the blood supply is restored in sunlight for 2 hours then steamed Antioxidants after a period of ischemia or hypoxia.8 at extremely high temperatures. This The antioxidant capability of catechins Studies have shown a link between fla- process deactivates the oxidative enzymes may be the best-known benefit of drink- vonoid consumption and a significant effectively, leaving the polyphenols in ing tea. In the human body, compounds reduction in coronary heart disease.9 This 64 September/October 2014 General Dentistry www.agd.org finding was confirmed in a 2001 study by Reducing cancer risk compounds known as chromogens, which Arts et al, who found a significant inverse The primary form of tumor cell degrada- are present in both coffee and tea, and have relationship between tea consumption and tion induced by radiation and chemother- an affinity for dental enamel.23 The tannins ischemic heart disease.10 Moreover, a 2011 apy occurs via apoptosis, a programmed and other polyphenolic compounds in tea study by Deka & Vita reported that the cell death. Excessive apoptosis causes worsen the situation by increasing chromo- flavins in black tea and catechins in green atrophy, whereas an insufficient amount gens’ ability to attach to enamel.23,24 tea inhibit platelet aggregation in rabbits; results in uncontrolled cell proliferation, Despite its potential esthetic disadvan- this helps reduce cardiovascular disease as seen in cancer.16 A 2012 study on green tage to teeth, tea consumption has been caused by plaque buildup.11 Many of the tea catechins by Connors et al reported shown to help improve overall oral health. aforementioned studies had limitations, that treatment with EGCG can trigger Green tea extract has shown inhibitory and additional research is necessary. apoptosis in prostate cancer cells (as effects on certain bacteria that are respon- evidenced by DNA fragmentation and sible for causing dental caries and peri- Neurological benefits cellular morphology).17 odontitis.25 A 2013 study by Araghizadeh After tea is consumed, the polyphenols are Another 2012 study found that Chinese et al reported that green tea extract exhib- modified chemically by intestinal enzymes women who drank an average of 2-3 cups ited inhibitory activity on Streptococcus rendering them fit for absorption by the of tea (mostly green) every day reduced mutans, the primary bacteria responsible gastrointestinal tract.12 Once absorbed, the risk of digestive system cancers— for dental caries, as well as other periodon- the compounds travel in the bloodstream, specifically colorectal, stomach, and topathic bacteria, including P. gingivalis, where they are delivered to various tis- esophageal cancers—by 21%.18 According A. actinomycetemcomitans, and P. interme- sues and organs. Certain polyphenols are to epidemiological evidence, black tea dia.25 A 2010 study by Koyama et al dem- unable to cross the blood brain barrier consumption generally is not associated onstrated that consuming >1 cup of green (BBB), a separation between blood and with a reduced risk of cancer.19 While tea/day was associated with a significantly the extracellular fluid of the brain that many of these studies are hopeful, there decreased risk for tooth loss.26 manages the passage of various metabo- are also reports that tea has no association Oolong tea has also been shown to help lites, drugs, and nutrients.12 However, the with cancer, with some actually recording reduce dental caries.27 The mechanism polyphenolic compounds in tea (specifi- an increased risk of cancer.19 depends on the oolong tea polyphenols, cally EGCG) have demonstrated an ability which inhibit the function of glucosyl- to cross the BBB, which can impact brain Other health benefits transferase, an important enzyme that function, neurodegenerative disorders, and Black tea is the most popular variety in allows S. mutans to attach to enamel.27 psychiatric disorders.12 the western world, and green tea is the A 2013 in vitro study reported that green A number of new studies have suggested favorite in Asian countries.1 Cigarettes tea polyphenols (specifically EGCG) dis- that the compounds found in green tea also are one of the most highly consumed played an inhibitory effect on the growth may be helpful in treating patients with products in Asia; however, Asian coun- and development of oral squamous cell car- Alzheimer’s disease and other forms of tries—Japan in particular—have surpris- cinoma cells.28 A 2005 study by Halder et dementia.13 Alzheimer’s disease produces ingly low incidences of arteriosclerosis and al studied patients with oral leukoplakia, a nonfunctional proteins (known as b-amy- lung disease per capita.20 This quandary is precancerous lesion that has been reported loid plaques) that attach to nerve cells in known as the Asian Paradox.20 Scientists in half of all cases of oral cancer.29 A group the brain.