Health Professional Newsletter
Welcome to the seventh 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
Regular tea consumption has favourable outcomes on markers of coronary heart disease risk
Researchers at University College London have demonstrated that tea drinking appears to protect men against the development of coronary heart disease (CHD).
CHD is a cause of significant morbidity and mortality in Western populations. An association between tea drinking and reduced risk of CHD and stroke has been demonstrated in cohort and case-control studies but results have been inconsistent. Non-human studies and acute studies in human populations have shown that tea has antioxidant properties, reduces platelet aggregation and has favourable effects on endothelial function. Chronic tea administration studies have yielded inconclusive results for other markers of CHD, including low density lipoprotein oxidation, oxidative DNA damage and lipid levels.
The present double blind, placebo controlled study measured the effect of tea drinking on C-Reactive Protein (CRP), platelet count, platelet activation (measured as percentages of monocytes, neutrophils and total leukocytes), total plasma antioxidant status and soluble P-Selectin at baseline and post treatment.
75 healthy males aged 18-55 years were randomised to receive tea or a placebo. Following an initial 4-week washout phase, participants were randomised to either receiving tea or a placebo for 6 weeks. The tea and placebo drink were similar in taste and caffeine content but differed in the presence of active tea constituents. Both the tea and placebo drink were in powdered form. Four sachets were consumed each day (made up with 250ml hot water) which equated to drinking 4 strong cups of black tea.
After six weeks, platelet activation and CRP levels were significantly lower in the tea compared to the placebo group. There were no changes or differences between groups in total antioxidant capacity, sP-Selectin or platelet count.
This is a small yet important study that has demonstrated beneficial effects for healthy men in reducing risk factors for CHD through effects on reduced inflammation. Whether this would be clinically important is unclear. Further studies are now required to determine whether these results would be reproduced in a larger study and indeed whether patients with established CHD could benefit from drinking at least 4 cups of tea per day.
Steptoe, A. Gibson, E. L., Vuononvirta, R., Hamer, M., Wardle, J., Rycroft, J. A., Martin, J. F., Erusalimsky, J. D. (2007) 'The effects of chronic tea intake on platelet activation and inflammation: A double-blind placebo controlled trial.' Atherosclerosis 193, 277-282
Tea drinking appears to preserve bone density in older women
The results of an Australian study has added further weight to the body of evidence showing that tea drinking may help preserve bone density at the hip in older women.
Hip fractures are a major cause of morbidity in older women. After age, the most important risk factor in this population is low areal Bone Mineral Density (aBMD). Countless studies have demonstrated that dietary and lifestyle factors, including calcium, protein and sodium intakes influence aBMD and the consequent risk of hip fracture. Furthermore, several studies have also shown that tea drinking has been associated with a higher aBMD and a reduced risk of hip fracture.
In this recent Australian study researchers recruited 1500 eligible women aged over 70 years to take part in a 5 year prospective randomised control trial. They were randomly assigned to receive 1200mg/day calcium carbonate or placebo.
Tea consumption data were collected using 24 hour dietary recall in a subset of 275 subjects, while all the subjects completed a self-administered food frequency questionnaire on beverage consumption at the end of the trial. Information on energy intake, calcium and alcohol was also collected. BMD measurements were performed at 4 sites (hip, femoral neck, trochanter and intertrochanter) at year 1 and year 5.
Results indicated that in this population of elderly women, drinking tea was independently associated with higher aBMD at the hip (2.8%) and trochanter (4.3%) and with lower rates of aBMD loss over 4 years, again at the hip and trochanter. Both groups did lose BMD over the 4 year period; however tea drinkers lost less than non-tea drinkers (9 - 13 mg/cm2 compared to 23 - 42 mg/cm2 in non-tea drinkers).
Components of the tea that are responsible for this apparent effect are unknown. The researchers are confident they have controlled for potential confounding variables – particularly the addition of milk to tea. In fact tea drinkers did have a significantly higher intake of calcium than non-tea drinkers. Phytochemicals in tea have been proposed by others to be important. Tea is a major dietary source of flavonoids and lignans, some of which have oestrogen-like properties. Synthetic phytoestrogens have a positive effect on BMD, but it is unclear how oestrogens-like compounds present in tea may affect BMD.
Studies to determine the mechanisms of this apparent effect of tea on BMD are needed before more confident statements can be made about the beneficial effects of tea drinking on bone mineral density.
Devine, A. Hodgson, J. M. Dick, I. M. Prince, R. L. (2007) 'Tea drinking is associated with benefits on bone density in older women.' American Journal of Clinical Nutrition 86, 1243-7.
Risk of colorectal cancer in green and black tea drinkers
A recent study from Singapore has found that black tea is not associated with an increased risk of colorectal cancer, but it has thrown doubts on green tea consumption and the risk of developing this cancer.
Most test tube and animal experiments support both green and black tea as preventative agents for the development of colorectal cancer. On the other hand epidemiological studies do not support an association between tea consumption and colorectal cancer risk reduction.
The current study used subjects who were already participants of the Singapore Chinese Health Study; a population-based prospective investigation in to diet and cancer.
61,320 subjects aged 45 – 74 years were eligible to take part in the study. Information about diet during the past 12 months was collected by Food Frequency Questionnaire (FFQ). Frequency of intake of green and black tea was assessed separately; subjects were asked to choose their intake during the past 12 months from 9 pre-defined categories ranging from never or hardly ever to six or more times per day. Subjects were followed for a mean of 8.9 years with a diagnosis of colorectal cancer as the main outcome measure. 845 subjects developed invasive colorectal cancer during the course of the study.
Neither total tea, green tea nor black tea consumption was associated with colorectal cancer risk. However, when the data were considered separately for men and women differences were apparent.
Men who reported drinking green tea one to three times per month or more frequently showed a significant 30% increased risk in developing colorectal cancer. There was also a highly significant, dose-dependent positive association between green tea consumption and risk of advanced colorectal cancer i.e. men drinking 6 or more cups of green tea a day had an 85% increased risk of developing advanced colorectal cancer. No such association was shown in women. Black tea consumption was not associated with colorectal cancer risk in either men or women.
This study highlights the limitations of test tube and animal studies in predicting the risk of disease in humans. There are still only a handful of studies that have examined the effect of green and black tea on colorectal cancer – mostly in Japanese populations. It is unclear how these new results would translate to a European population where green tea drinking habits are much different.
Can-Lan Sun, Jian-Min Yuan, Woon Puay Koh, Hin-Peng Lee & Mimi C.Yu. (2007) 'Green tea and black tea consumption in relation to colorectal cancer risk: the Singapore Chinese Health Study.' Carcinogenesis 28, (10) 2143 – 2148.
Tea and renal cancer
Drinking more tea and coffee may be associated with a lower risk of renal cancer according to a large review conducted by the Harvard Medical School.
Rates of renal cancer have been rising steadily over the past 3 decades, yet the cause remains unclear. It has been suggested, given the kidney’s filtration functions, that renal cancer may be affected by the quantity and type of beverages consumed. Specifically it is proposed that beverages containing caffeine and/or antioxidants may reduce renal cancer.
The results of 13 prospective studies which evaluated associations between renal cancer and coffee, tea, milk, soda and fruit and vegetable juice intake were pooled together in this current review. Data for 530,469 women and 244,482 men were included in the analysis. Beverage intake was assessed using validated food frequency questionnaires or diet histories and categorised using uniform cut off points. Tea drinkers were divided into two groups depending on the frequency of consumption: once per month to less than once per day and once or more per day. One serving of tea or coffee was defined as 8oz (237g). Follow-up periods varied from 7 – 20 years across the studies with a diagnosis of renal cancer as the main outcome measure.
Results from this analysis found that the consumption of tea or coffee was not associated with an increased risk of renal cancer. In fact there was a non-significant 15% lower risk of renal cancer among participants who drank one or more cup of tea per day compared to non-tea drinkers suggesting that frequent tea consumption may be associated with a lower risk of renal cancer.
Despite the large numbers involved in this study the evidence of a protective effect of tea consumption on renal cancer risk remains to be established. However there is strong evidence that drinking tea does not result in an increased risk of renal cancer.
Lee, J.E. et al. (2007) ‘Intakes of coffee, tea, milk, soda and juice and renal call cancer in a pooled analysis of 13 prospective studies’ International Journal of Cancer 121, 2246-2253.
