Health Professionals Newsletter
Welcome to the eleventh newsletter from the United Kingdom Tea Council. This service will keep you up to date with current tea4health activities and events and inform you of the latest published research. We'll keep you updated on a quarterly basis with news and views from across the tea industry.
Tea consumption associated with a lower risk of cognitive impairment and decline
Cross-sectional and longitudinal analysis of data from the Singapore Longitudinal Aging Studies (SLAS) has revealed that a high consumption of black and oolong tea is associated with a reduced risk of cognitive impairment and decline.
This study was undertaken in an attempt to support or refute the findings of an earlier cross-sectional study that concluded higher green tea, but not black or oolong tea, consumption was associated with a lower prevalence of cognitive impairment in an elderly Japanese population. Prior to this, animal studies have indicated that tea has neuroprotective effects.
A total of 2501 participants, aged ≥ 55 years, from the SLAS provided baseline data for the cross-sectional part of the study. Measures taken at baseline included:
cognitive function measured by Mini Mental State Examination (MMSE). Scores ranged from 0-30, with higher scores indicating better cognitive function. Cognitive impairment was defined as a MMSE score of ≤ 23.
detailed information on tea consumption:
type: English/Ceylon, Chinese tea including Chinese black and Chinese Oolong, and green tea
frequency of consumption which was scored as follows 0 = never or rarely, 1 = <1 cup per week, 2 = > one cup per week but < 1 cup per day, 3 = 1-2 cups per day, 4 = 3-5 cups per day, 5 = 6-9 cups per day, 6 = >10 cups per day. One cup was defined as 215mls
Cumulative scores were devised for each type of tea to estimate total tea consumption, where a score of 0=non-tea drinker, 1-3 = low, 4-6 = medium, >7 = high. Other data collected included age, gender, education, cigarette and alcohol use, coffee consumption, fruit and vegetable consumption, fish consumption, medical conditions including depression, level of physical activity, weight, height and blood pressure.
Almost half the participants consumed Chinese black or Oolong tea with around 18% drinking at least one cup per day. Around 40% consumed English/Ceylon black tea - with 18% consuming these types of tea daily. Twenty three percent drank green tea but less than 7% drank green tea daily. Thirty eight percent of participants never or rarely drank tea.
Fifty six percent of participants drank at least one cup of coffee per day and 73.5% drank more than one cup per week.
Analysis revealed that total tea consumption was significantly associated with higher MMES score - 19.1% of non-tea drinkers scored 23 or below, indicating cognitive impairment whilst only 3.1% of high tea drinkers scored 23 or below. However, high-tea consumers were more likely to be male, younger, consume more alcohol, eat more fruit, vegetables and fish, be more active and suffer less depression. But once potential confounders were taken into account it was confirmed that a high level of tea consumption was significantly associated with a lower risk of cognitive impairment.
For the longitudinal study participants with an MMES score of 23 or below were excluded. The remaining participants (n=1438) underwent a reassessment of cognitive function 1-2 years later. Tea drinking habits were not reassessed.
Once confounding risk factors were taken into account it was confirmed again that those with a high level of tea consumption were less likely to suffer cognitive decline. In contrast, coffee intake was not significantly associated with either cognitive impairment or cognitive decline.
Although the possible mechanisms by which tea exerts these neuroprotective effects are unknown, the researchers proposed that the tea flavonoids may play a role. These possess strong antioxidant properties which may offer cell protection from free radical attack. Furthermore tea contains other compounds, such as theanine and Vitamin C, which may also be neuroprotective. It maybe that it is a combination of these components, rather than one single compound that is offering cognitive protection.
Due to the low number of green tea only drinkers it was not possible to make direct comparisons with the Japanese study. But these findings do support the notion that high tea consumption, particularly for black and oolong tea (the major types of tea consumed) is associated with reduced cognitive impairment and cognitive decline. The researchers concluded by suggesting that as cognitive decline is a predictor of the development of dementia, the potential of tea drinking in protecting against this cognitive decline has great significance.
Tze-Pin Ng, et al (2008) Tea consumption and cognitive impairment and decline in older Chinese adults. Am J Clin Nutr. 88(1):224-31.
Further evidence supports the role of tea in good dentition
A study that examined teeth exposed to various fluids has found that green and black teas have a minimal erosive effect and in fact are similar to water, which has no erosion potential. In contrast to this, exposures to cola and fruit juice are moderately erosive whereas vinegar is highly erosive.
This study set out to identify the erosive effects of green and black tea (without milk or sugar) on adult human teeth when incubated for a period of time. The effect of a cola drink and orange juice were also examined. Tap water and vinegar were used as positive and negative controls.
This study was carried out in vitro using 36 recently extracted adult human pre-molar teeth. Thus the influence of the oral environment was not considered in this study.
Initial baseline and subsequent assessments were made by visual inspection, sequential photographs and radiographs using standardised techniques. For a period of 20 weeks the crown and cervical root portions of the teeth were immersed in static fluids - either one of the four test beverages or one of the control fluids at room temperature. They were examined on a weekly basis, and photographic and radiographic recordings were taken once every 4 weeks over the 20 week period.
Structural observations included: enamel translucency, colour, texture, presence and exposure of underlying dentin with subsequent colour and texture change. Radiographic and photographic images were analysed to evaluate geometric and dimensional changes, including loss of enamel.
Green and black teas were prepared by infusing 2.5g of tea leaves in 200ml of boiled water for 3 minutes. Green and black tea contained similar amounts of caffeine and pigment but differed in their content of phenolic compounds. Green tea contained approximately 30% non-oxidised phenolic compounds compared with 5% in black tea. Oxidised phenolic compounds constituted the remaining 25% of black teas phenolic compounds.
The pH, caffeine and acid content of the test beverages and controls was as follows:
At the beginning of the study all teeth displayed normal colour, translucency, surface texture, consistency and morphology.
The specimens incubated in vinegar saw complete erosion of the enamel cap and the underlying dentin became progressively dark brown by the end of the 20 weeks. Vinegar incubated specimens displayed most enamel loss, averaging 0.3-0.75mm per week.
Incubation in both green and black tea produced only minor structural changes to enamel and dentin. With cola and by 4 weeks there was recognisable enamel deterioration when incubated; by week 20 enamel thickness had declined considerably. By week 3 the enamel and dentin has discoloured to dark yellow. The erosion of the surface enamel by week 10-11 exposed the underlying dentin which discoloured further to brown; by week 20 the discolouration had intensified. The average enamel loss from specimens incubated with cola and orange juice were similar ranging from 0.1-0.23mm per week.
Structural changes to specimens incubated in orange juice occurred much more slowly and with less intensity than changes caused by vinegar and cola. However, by 12 weeks enamel was discoloured and the surface roughness was increased. By 20 weeks the colour of the enamel had intensified to brown.
The erosive nature of green and black teas appears to be so low that specimens resembled those incubated in tap water. However, there was low grade damage that may be attributed to the presence of tannic acid that slightly decreased the pH at the tooth surface.
Certain constituents present in tea are thought to be beneficial to dental health. Tea is a source of natural fluoride which protects enamel from acid attack. It has also been reported that tannins in tea inhibit the enzyme in the mouth from breaking down starch to sugars. Furthermore some studies have shown that the tea polyphenols and tannins prevent the growth of the bacteria responsible for caries.
As a result of the findings from this study and because of the plethora of reported health benefits of tea, including dental health benefits, the authors concluded that tea should be recommended as a substitute for acidic drinks.
Bassiouny MA, et al (2008) Topographic and radiographic profile assessment of dental erosion. Part III: Effect of green and black tea on human dentition. Gen Dent. 56(5):451-61.
New compounds found in tea
A recent study identified more than 96 phenolic compounds in a sample of 41 green teas and 25 fermented teas. Previous studies have never detected more than 50 phenolic components.
Tea is made from the dried fresh (green tea) or enzymatically oxidised (oolong, black tea) young buds and leaves of varieties of Camellia sinensis L. (Theaceae). This plant was originally found in South China but is now common to many other countries, such as Japan, India, Sri Lanka, Indonesia, Australia, Kenya and Chile. On the basis of production procedures tea has been divided into green tea, oolong tea and black tea.
Tea is now one of the most widely consumed beverages in the world and is the subject of much research investigating potential health benefits. Many compounds are present in tea and it has been shown that tea contains purine (xanthine), alkaloids, phenolic compounds (mainly catechins, O-glycosylated flavonols, C-glycosylflavones, proanthocyanidins, phenolic acids and their derivatives), terpenoids, and other compounds (fatty acids, essential oils, amino acids, etc). Oolong and black teas also contain the fermented oxidation products of catechins, theaflavins and thearubigins. The phenolic compounds present in tea have been found to have potential health benefits in a number of studies.
The objective of the current study was to systematically identify glycosylated flavonoids, catechins, proanthocyanidins, phenolic acid derivatives and purine alkaloids in a single chromatographic run - something that has not been performed previously.
The phenolic profiles of 41 green teas and 25 fermented teas made it possible to divide the teas into 5 goups:
Group 1 - This group contained 3 high-grade green teas and 2 white teas made from the younger buds and leaves harvested in the early-leaf growing stage. These contained a lower concentration of glycosylated flavonols and epigallocatechin gallate (EGCG) and a higher fraction of acylated flavonol glycosides than group 2 teas.
Group 2 - Contained 36 common Green teas (including 7 decaffeinated green teas) made from mature leaves. This affected their phenolic content as these teas contained significantly higher levels of EGCG and glycosylated flavonols than group 1 teas. Tea plants from this group which were grown in areas experiencing higher levels of sunshine (Yunan province) had higher catechin and flavonoid levels compared to other locations in China. Many green teas contain up to 20% total phenolics by dry weight and most of these compounds can be dissolved in hot water. Thus the average cup of green tea is able to supply over 250mg of flavonoids.
Group 3 - Oolong teas formed part of this group of 14 partially fermented teas. They contained considerably less EGCG than green teas but the same concentration of glycosylated flavonols. The content of theaflavins (the oxidation products of EGCG) and other catechins was higher than green tea.
Group 4 - Consisted of 9 fully fermented black teas that contained only traces of EGCG but contained higher levels of theaflavins than group 3 teas.
Group 5 - Two highly over-fermented black teas formed this group. They contained only traces of EGCG, flavonol glycosides and theaflavins. These teas are generally consumed by older people in China.
With this new classification of teas based on their phenolic compounds it may be possible for future research to single out individual tea types or teas grown in specific regions when investigating particular health benefits that a tea may offer.
Lin LZ, Chen P, Harnly JM (2008) New phenolic components and chromatographic profiles of green and fermented teas. J Agric Food Chem. 10;56(17):8130-40. Epub 2008 Aug 8.