Health Professionals Newsletter

Welcome to the latest 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.

Research Update

Drinking 3 or more cups of tea a day may help to reduce the risk of breast cancer in younger women
Findings from a large case-control study in the US has found that women under the age of 50 who consumed modest amounts of tea had a 37% reduced risk of breast cancer (BC) compared to non-tea drinking women.

There is a great deal of in vitro evidence showing that epigallocatechin gallate and theaflavin-3,3'-digallate, two polyphenols found in green and black tea respectively, suppress mammary tumours. Green and black tea extracts also demonstrate antimutagenic, antiproliferative and antineoplastic activities in vitro.

However, epidemiological studies on the effects of green or black tea on BC have been largely inconclusive. In the present study data from a large population-based, case-control study was examined with a view to shedding more light on the potential role of tea consumption on BC risk.

Cases were women with a first primary BC diagnosis identified from cancer registries in 3 US states. Age range at diagnosis was 20 - 74 years. A total of 5,059 cases were included in the analysis after excluding those in which data on tea consumption was lacking (n=23).

Controls were selected from the same state and were matched to cases within a 5-year age strata; 4,486 controls were included in the analysis following similar exclusions (n=15) for missing data.

Ninety eight percent of the study population was Caucasian.

Information on tea consumption was gathered by telephone interview. Women were asked how often, on average, they consumed green or black tea, but not herbal tea, approximately 5 years before diagnosis in cases, or a comparable reference period in controls. Usual tea consumption could be reported per day, week, month or year. This was then converted to cups per day; 0, <1, 1<2, 2<3, 3 or more. Data was also collected on known BC risk factors and this information was used to control for potential confounding variables including: menopausal status / age at menopause, number of live born children delivered / age at first child birth, body mass index, hormone replacement therapy (HRT) use, education, alcohol consumption, physical activity, family history of BC, and history of mammogram screening.

Interestingly results were unchanged after adjustment for these confounding variables and only age and geographical area-adjusted results were presented.

Overall 44.7% of cases and 45.7% of controls reported ever drinking tea 5 years before diagnosis /reference date.

Women aged ≤ 50 years who reported drinking ≥ 3 cups of tea per day, 5 years prior to the interview, had a 37% reduced BC risk compared with women reporting no tea consumption (age and site-adjusted OR 0.63; 95% CI, 0.44 - 0.89; P=0.01). After adjusting for all confounding variables results were essentially unchanged (OR 0.62; 95% CI, 0.43 - 0.83; P=0.004).

No similar associations were observed in the two other age groups: 51-65 years and >65 years.

An inverse trend was also noted for pre-menopausal women (who tended to be younger) consuming ≥ 3 cups of tea per day although this did not quite reach significance (age and site-adjusted OR 0.71; 95% CI, 0.50 - 1.01; P=0.05).

For the women aged ≤ 50 years who reported drinking ≥ 3 cups of tea per day the inverse trend was also consistent with BC subtypes: 59% reduced risk for in situ BC (non-invasive BC confined to the breast ducts and lobules), 29% reduced risk for invasive BC, 31% reduced risk for invasive ductal BC and a 67% reduced risk for invasive lobular BC. However the authors admit these results were based on small numbers being analysed.

There were no relationships according to tea consumption in older women regardless of BC subtype.

This study has a number of limitations which may have affected the findings. As with all retrospective studies recall bias is a possibility, as women were being asked not only about tea consumption 5 years before diagnosis, but also about lifestyle factors and body weight which may be difficult to recall. Furthermore a differentiation between green and black tea was not made. However the authors suggest that because of the time period of data collection (1998 and 2001), and as the majority of women were Caucasian, it can be assumed that the bulk of tea consumed would have been black tea.

While the findings from this large case-control study suggest that drinking ≥ 3 cups of tea per day may reduce the risk of BC in younger and possibly pre-menopausal women, further studies are required to confirm these results.
Kumar, N., Titus-Ernstoff, L., Newcomb, P. A., Trentham-Dietz, A., Anic, G. and Egan, K. M. (2009). Tea consumption and risk of breast cancer. Cancer Epidemiol. Biomarkers Prev. 18(1): 341-45.

Tea may help to reduce the risk of stroke
According to findings from a recent meta-analysis, drinking 3 or more cups of tea a day may help to reduce the risk of stroke and death from stroke by 21%.

A small number of human studies have suggested an association between tea consumption and reduced risk of stroke. While studies inducing stroke in animal models provide further evidence to support the beneficial effects of either epigallocatechin gallate or tea catechin extracts on stroke severity. The purpose of the current study was to thoroughly examine the human clinical and epidemiological data available to determine whether black or green tea, as a hot beverage, has an impact on the risk of stroke in humans.

A systematic review and meta-analysis was conducted and included both clinical trials and observational studies. An electronic search of the PubMed and Web of Science databases yielded 59 citations. Two reviewers independently reviewed each abstract for eligibility. Screening of these citations resulted in the identification of 11 studies (8 cohort, 2 case-controls and one cross-sectional study) that could provide original data on stroke in relation to tea consumption.

Ten studies from 6 countries were included in the final meta-analysis: China, Japan, Finland, Netherlands, Australia and the US. Three studies included data on men only and 3 on women only. Three studies combined the effects in men and women and one study presented its results for men and women separately. These studies included 7 populations that drank primarily or exclusively black tea and 3 that drank primarily green tea.

The pooled meta-analyses show tea consumption to be associated with a reduced risk for occurrence of and mortality from stroke. Subjects drinking ≥ cups of tea per day appear to reduce their risk of a fatal or non-fatal stroke by around 21% compared with non-tea drinkers. This effect was observed across all the 6 countries studied despite different drinking customs.

A further meta-analysis was also conducted in 5 sub-groups to see if associations relating to the type of tea consumed (green or black) or ethnicity had any further effect. Results from these sub-group analyses showed similar results to the over-all risk reduction, meaning that the effect does not appear to be specific to black or green tea, or to Asian or non-Asian populations.

Being a review of observational studies, the mechanism by which tea may protect against stroke remains speculative. Whilst antioxidant function and anti-inflammatory actions are popular theories, other mechanisms may include beneficial effects on blood pressure and endothelial function, as well as the neuroprotective action of theanine.

The authors suggest that their findings may be one of the most actionable lifestyle changes to significantly reduce the risk of stroke.
Arab, L., Liu, W. and Elashoff, D. (2009). Green and black tea consumption and risk of stroke. A meta-analysis. Stroke, DOI:10.1161/STROKEAHA.108.538470.

Long term tea drinking is associated with a reduced prevalence of Diabetes in an elderly population
A cross-sectional study examining long-term tea consumption has observed a reduced prevalence of type 2 diabetes (DM 2) among elderly people living in the Mediterranean islands.

A number of epidemiological studies have indicated that tea reduces the risk of many chronic diseases, including cardiovascular disease (CVD) and cancer. However, much of these data are in middle-age populations in whom, the authors propose, the burden of disease is not as high as in elderly populations.

The current study, the MEDIS epidemiological study, was undertaken to define tea consumption, diet, lifestyle and other socio-economic factors in an elderly population and relate this to the prevalence of CVD risk factors (hypertension, dyslipidaemia, diabetes and obesity).

A random, multi-stage, sampling method selected men and women >65 years residing in Cyprus and 6 Greek islands. Those with existing CVD and those residing in assisted living centres were excluded from the study.

Four hundred and thirty seven men and 500 women agreed to participate in the study. Field investigators (including physicians, dietitians and nurses) collected all data using a quantitative questionnaire and standard procedures.

Consumption of 15 food groups and beverages were estimated using a semi-quantitative food frequency questionnaire (FFQ). For each item, weekly consumption was recorded as never, rare, 0-1 times, 1-2 times, 3-5 times and daily. For tea consumption, participants were asked about which tea they consumed (black, green, oolong or white) and the frequency they consumed a cup (150ml) in a week; never or <1 cup per week, 1-2 cups per day, 3-5 cups per day and > 5 cups per day. Coffee consumption was recorded in the same manner. The consumption of decaffeinated beverages was not considered because of limited local availability. Consumption of alcohol was standardised as ethanol intake. Overall dietary habits were also assessed for adherence to the Mediterranean dietary pattern using the Med Diet Score tool. Physical activity was evaluated using a shortened version of the international physical activity questionnaire for the elderly. Data were also collected on age, gender, financial status, education and smoking status.

DM2 was determined by fasting plasma glucose tests and was analysed in accordance with the American Diabetes Association diagnostic criteria; fasting blood glucose levels greater than 125mg/ dL or the use of special medication were used to define Diabetes. Weight and height were measured to calculate Body Mass Index (BMI) scores; obesity was defined as > 29.9kg/m2. Blood pressure levels were retrieved from medical records; blood pressure levels ≥ 140/ 90mmHg, or the use of antihypertensive medications, defined an individual as hypertensive. It is unclear how blood lipid levels were determined as the methods state 'fasting blood lipids were recorded'; hypercholesterolemia was defined as total serum cholesterol levels >200mg/ dL or if lipid lowering agents were used.

The prevalence of DM2 in this cross-sectional sample was 21% in men and 23% in women. Around half the participants reported drinking tea at least once per week with a mean intake of 1.6 ± 1.1 cups per day. Ninety eight percent of tea consumed was either black or green tea. Thus for the purpose of reporting the authors decided to use combined tea consumption in all analyses. The participants reported they had followed the same tea consumption habits for the past 30 years.

There were some notable differences in the sample according to volume of tea consumption. People who consumed more tea tended to be older, more likely to follow a Mediterranean-type diet and were more like to be physically active.

An inverse relationship was found between tea consumption, fasting blood glucose levels (p = 0.008) and the prevalence of DM2 (p = 0.001). After adjusting for age, gender, education, physical activity, BMI, total cholesterol and smoking status this effect was slightly attenuated for fasting glucose levels (p<0.05).

Further analysis revealed that drinking 1 - 2 cups of tea per day was associated with the greatest benefit on blood glucose levels; drinking more provided no further benefit. An increase of one cup per day was associated with a 70% lower likelihood of having diabetes (95% CI 41%-86%), after adjusting for confounding variables.

The authors point out a number of potential limitations of this current study. Being a cross-sectional study there is always the possibility of recall bias as the results rely on self reported data which is notoriously unreliable. Furthermore the closed population of this study means extrapolation to a wider Western population should be done with care and provisos. In addition it is not clear from the study how data for diabetes diagnosis, blood glucose and blood lipid levels were obtained.

Nevertheless this study has demonstrated that tea consumption among an elderly population from the Mediterranean islands is associated with a reduced prevalence of diabetes through effects on plasma glucose levels. Cohort or case-control studies in other elderly populations are now required to confirm these findings.
Panagiotakos, D.B., Lionis, C., Zeimbekis, A., Gelastopoulou, K., Papairakleous,N., Das, U. N. and Polychronopoulos, E. (2009). Long-Term Tea Intake is Associated with Reduced Prevalence of (Type 2) Diabetes Mellitus among Elderly People from Mediterranean Islands: MEDIS Epidemiological Study. Yonsei Med. J. 50(1): 31-38.