October 1, 2015
by Wendy E. Ward, Professor & Canada Research Chair, Faculty of Applied Health Sciences, Brock University
When did you last have a cup of tea? Besides water, tea is the most commonly consumed beverage worldwide. In Canada, tea is increasingly popular among younger age groups. Specialty tea – tea that is not a typical black tea – is particularly popular among all age groups, including Millenials, also known as Generation Y. Potential health benefits gained through drinking tea is one factor driving consumer interest. Compared to other teas, green tea has been extensively studied in relation to health. This is due to the high content of epigallocatechin gallate (EGCG), a flavonoid that is used in a variety of dietary supplements as well as cosmetics. Flavonoids such as EGCG may act as an antioxidant, anti-inflammatory and antimicrobial and it is these properties that support a role of green tea in maintenance of overall health.
Health Canada allows a food function claim for green tea (as unfermented leaves and/or bud from Camellia sinensis).1 Products that are included in this function claim are the following: a green tea infusion brewed following the manufacturers directions that contains at least two grams or more tea leaves per 250 mL; one tea bag containing two grams tea leaves; or a reconstituted green tea product containing at least 0.8 grams freeze dried or spray dried tea infusion per reference amount and serving of stated size when prepared to manufacturers directions.1 Since this function claim pertains to antioxidant activity in relation to blood lipids, the following wording can be used on a product label: “consumption of 1 cup (250 ml) of green tea helps to protect blood lipids from oxidation; consumption of 1 cup (250 ml) of green tea has an antioxidant effect in blood or on blood lipids; or consumption of one cup (250 ml) of green tea increases antioxidant capacity in the blood”.1 Flavonoids are not just found in tea, but in a variety of plant foods including fruits and vegetables, and some herbs, spices and essential oils. Typically, habitual consumers of green tea obtain at least half of their daily dietary flavonoid intake from this source.
With respect to periodontal health, the few studies on the topic of green tea and periodontal health attempt to answer two different research questions: Is there a protective association between higher green tea consumption and tooth retention or periodontal disease? Does use of green tea containing gels, as an adjunct to non-surgical scaling and root planing, improve periodontal outcome? The known antimicrobial and anti-inflammatory activity of flavonoids that have been demonstrated using cell culture and animal models provides biological plausible mechanisms by which green tea or its flavonoids may attenuate periodontal disease and assist with recovery after periodontal therapy. Moreover, several epidemiological studies suggest that bone mineral density (BMD) at hip or spine is higher among habitual tea drinkers; it is important to note that there is currently insufficient evidence to delineate how or if habitual tea consumption relates to risk of fragility fracture (reviewed in 2). It is hypothesized that alveolar BMD may also benefit with habitual consumption of green tea since studies have shown that greater losses of BMD at other sites are associated with less retention of teeth.3,4 This hypothesis regarding green tea and alveolar BMD awaits confirmation.
Tea Primer: Are all “teas” the same?
Before discussing the details of these studies, it is important to understand some tea terminology (Table 1). True “tea” comes from the tea plant, Camellia sinensis, and there are six types: white, yellow (very rare), green, oolong, black and puer. All contain caffeine and it is only the type of and extent of processing that makes these teas different from each other, including distinct differences in flavonoid profiles and overall taste. For example, a predominant flavonoid in green but not other teas is EGCG. In contrast, rooibos and herbal beverages are infusions or tisanes because of their origin from African red bush (Aspalathus linearis) or herbal plant material, respectively, rather than the tea plant (Camellia sinensis). Unlike tea, rooibos and herbal infusions or tisanes do not contain caffeine and have their own distinct flavonoids profiles. Understanding potential health benefits of these flavonoids is an active area of research.
TABLE 1. Comparison of Teas versus Infusions/Tisanes
Relationship Between Green Tea Consumption and Tooth Retention or Periodontal Disease
A cross-sectional study, using baseline survey data from the Ohsaki Cohort 2006 study in Japan, showed that men and women who consumed ≥ one cup of green tea per day had a lower odds ratio for tooth loss.5 This study includes data from approximately 25,000 participants between the age of 40 and 64, with similar proportions of men and women. Overall, there is some agreement in the literature that the level of flavonoids in one serving of green tea would be sufficient to inhibit activity and/or growth of harmful bacteria. Limitations of this study include the cross-sectional design, self-reporting of number of teeth and no direct information on oral health (prevalence of caries, periodontal disease).5 Further study using different designs is needed to more fully understand this relationship and potential mechanisms.
Another study, also from Japan, showed a small but statistically significant association between consumption of green tea and mean probing depth, mean clinical attachment loss and bleeding on probing.6 This study included men, aged 49 to 50, who self-reported green tea intake and underwent a periodontal health examination. The regression model showed a 0.02 mm decrease in mean probing depth, a 0.03 mm decrease in clinical attachment loss and a 0.63 percent decrease in bleeding on probing with every one cup of green tea that was consumed.6 Clinical significance of this finding is small but nonetheless suggest a positive effect of green tea on periodontal health.
Does Use Of Green Tea Containing Gels, As An Adjunct To Non-Surgical Scaling And Root Planing, Improve Periodontal Outcome?
Given that earlier studies showed anti-microbial effects of flavonoids from green tea – combined with findings from the aforementioned studies–it is biologically plausible that local administration of green tea flavonoids may assist with healing after mechanical debridement. A recent study published in the Journal of Periodontology reported enhanced reduction in probing depth and inflammation at four weeks post-periodontal therapy when a gel containing green tea extract was placed in the periodontal pocket immediately after therapy.7 A total of 30 patients were studied and each served as their own control as a split mouth design was used. Testing in vitro showed that the gel released approximately 96 percent of the bioactive by 108 hours. The mean change for probing depth was 2.06 mm for the site that received the green tea gel versus 0.97 mm for the control site. The authors speculate that the positive effects were due to inhibitory effects of EGCG on proinflammatory enzymes (lipoxygenases, cyclooxygenases) and bacterial activity.7 This study provides a basis for future studies investigating effectiveness of green tea extract as an adjunct therapy, as well as administration of other potential bioactives.
Caffeine In Green Tea: Is It A Problem For Alveolar And Overall Bone Health?
All teas contain caffeine, albeit at markedly lower levels than coffee (Table 2). For adults, Health Canada
advises that daily intake of caffeine from all sources should not exceed 400 mg per day. Caffeine intake is generally considered to be a risk factor for bone loss and/or osteoporosis, by stimulating excretion of calcium. However, there is evidence that caffeine, when consumed in moderation, may only be a problem for calcium status and bone health when dietary calcium levels are below recommended levels. Moreover, given that there is some evidence that flavonoids may have a positive effect on bone, understanding the relationship (and potential harm) of caffeine to bone health is complex, and more studies in humans that specifically examine the relationship of caffeine, flavonoids and bone health are needed. Interestingly, a cross-sectional study in Scottish women reported a positive relationship between flavonoid intake and BMD at the lumbar spine and hip, and over 50 percent of the flavonoid intake was due to consumption of tea.8
TABLE 2. Caffeine Content of Commonly Consumed Beverages Values obtained from Health Canada’s website
More data is needed before we can be confident that regular consumption of green promotes retention of teeth, possibly through higher BMD of alveolar bone and/or reduced risk of periodontal disease. Moreover, whether local administration of green tea extract or flavonoid such as EGCG improves periodontal outcomes after scaling and root planing requires further investigation.
Take Home Points:
Consumption of green tea can be part of a healthful lifestyle. Even with some uncertainty about benefits to human health, for some individuals a cup or two of green tea may be part of an effective strategy for managing the demands of everyday life. However, it is important to remember that as with all natural products, there can be harmful effects to health if consumed in excess.
• If consuming green tea, keep in mind the caffeine level and recommendation for upper level of caffeine intake per day.
• Supplements that contain isolated flavonoids or green tea extract will contain higher levels of one or more specific compounds than are naturally present in a food such as green tea.
To avoid consuming a potentially harmful level, it is important to consider what level is ‘safe’ based on current data. Consulting a pharmacist can provide guidance.OH
Wendy Ward is a Canada Research Chair in Bone and Muscle Development in the Faculty of Applied Health Sciences at Brock University. Her research program investigates how early diet programs adult bone health and may attenuate the risk of developing osteoporosis. Within this program her research group studies the mechanisms by which dietary estrogens (i.e. isoflavones in soy, lignans in flaxseed), vitamin D and fatty acids regulate bone metabolism.
Oral Health welcomes this original article.
1. Canadian Food Inspection Agency. Government of Canada. http://inspection.gc.ca/food/labelling/food-labelling-for-industry/health-claims/eng/1392834838383/1392834887794?chap=7#s13c7. Accessed August 4, 2015.
2. Nash LA, Ward WE. Tea and bone health: findings from human studies, potential mechanisms, and identification of knowledge gaps. Critical Reviews in Food Science and Nutrition. 2015;in press.
3. Iwasaki M, Nakamura K, Yoshihara A, Miyazaki H. Change in bone mineral density and tooth loss in Japanese community-dwelling postmenopausal women: a 5-year cohort study. Journal of Bone and Mineral Metabolism. 2012;30(4):447-453.
4. Krall EA, Garcia RI, Dawson-Hughes B. Increased risk of tooth loss is related to bone loss at the whole body, hip and spine. Calcified Tissue International. 1996;59(6):433-437.
5. Koyama Y, Kuriyama S, Aida J, Sone T, Nakaya N, Ohmori-Matsuda K, Hozawa A, Tsuji I. Association between green tea consumption and tooth loss: cross-sectional results from the Ohsaki Cohort 2006 study. Preventive Medicine. 2010;50:173-179.
6. Kushiyama M, Shimazaki Y, Murakami M, Yamashita Y. Relationship between intake of green tea and periodontal disease. Journal of Periodontology. 2009;80(3):372-377.
7. Chava VK, Vedula BD. Thermo-reversible green tea catechin gel for local application in chronic periodontitis: a 4-week clinical trial. Journal of Periodontology. 2013;84(9):1290-1296.
8. Hardcastle AC, Aucott L, Reid DM, Macdonald HM. Associations between dietary flavonoid intakes and bone health in a
Scottish population. Journal of Bone and Mineral Research. 2011;26(5):941-7.