Black tea – helpful or harmful? A review of the evidence

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Yvonne
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Black tea – helpful or harmful? A review of the evidence

Post by Yvonne » Sun 23 Dec 2007 10:58

Black tea – helpful or harmful? A review of the evidence

Abstract
Objective: To consider whether consumption of black tea has a positive or negative impact on health.

Design: Databases were searched for relevant epidemiological and clinical studies published between 1990 and 2004.

Results: Clear evidence was found for coronary heart disease (CHD), where an intake of 3 cups per day related to risk reduction. The mechanism could involve the antioxidant action of tea polyphenols. While experimental models have suggested that flavonoids attenuated cancer risk, epidemiological studies failed to demonstrate a clear effect for tea, although there is moderate evidence for a slightly positive or no effect of black tea consumption on colorectal cancer. Studies on cancer were limited by sample sizes and insufficient control of confounders. There is moderate evidence suggestive of a positive effect of black tea consumption on bone mineral density although studies were few. There is little evidence to support the effect of tea on dental plaque inhibition but evidence to support the contribution of tea to fluoride intakes and thus theoretical protection against caries. There was no credible evidence that black tea (in amounts typically consumed) was harmful. Normal hydration was consistent with tea consumption when the caffeine content was <250 mg per cup. A moderate caffeine intake from tea appeared to improve mental performance, although sample sizes were small. There was no evidence that iron status could be harmed by tea drinking unless populations were already at risk from anaemia.

Conclusions: There was sufficient evidence to show risk reduction for CHD at intakes of 3 cups per day and for improved antioxidant status at intakes of one to six cups per day. A maximum intake of eight cups per day would minimise any risk relating to excess caffeine consumption. Black tea
generally had a positive effect on health.

http://www.nature.com/ejcn/journal/v61/ ... 2489a.html
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Yvonne
Posts: 2421
Joined: Fri 27 Jul 2007 16:02

Re: Black tea – helpful or harmful? A review of the evidence

Post by Yvonne » Sun 23 Dec 2007 11:06

The effects of tea on psychophysiological stress responsivity and post-stress recovery:
a randomised double-blind trial


Andrew Steptoe1 , E. Leigh Gibson1, Raisa Vounonvirta1, Emily D. Williams1, Mark Hamer1, Jane A. Rycroft2, Jorge D. Erusalimsky3 and Jane Wardle1

(1) Department of Epidemiology and Public Health, University College London, 1-19 Torrington Place, London, WC1E 6BT, UK
(2) Unilever Research Colworth, Bedford, UK
(3) Wolfson Institute for Biomedical Research, University College London, London, WC1E 6BT, UK

Received: 12 June 2006 Accepted: 9 August 2006 Published online: 30 September 2006

Abstract
Rationale Tea has anecdotally been associated with stress relief, but this has seldom been tested scientifically.
Objectives To investigate the effects of 6 weeks of black tea consumption, compared with matched placebo, on subjective, cardiovascular, cortisol and platelet responses to acute stress, in a parallel group double-blind randomised design.
Materials and methods Seventy-five healthy nonsmoking men were withdrawn from tea, coffee and caffeinated beverages for a 4-week wash-out phase during which they drank four cups per day of a caffeinated placebo. A pretreatment laboratory test session was carried out, followed by either placebo (n = 38) or active tea treatment (n = 37) for 6 weeks, then, a final test session. Cardiovascular measures were obtained before, during and after two challenging behavioural tasks, while cortisol, platelet and subjective measures were assessed before and after tasks.
Results The tasks induced substantial increases in blood pressure, heart rate and subjective stress ratings, but responses did not differ between tea and placebo treatments. Platelet activation (assessed using flow cytometry) was lower following tea than placebo treatment in both baseline and post-stress samples (P < 0.005). The active tea group also showed lower post-task cortisol levels compared with placebo (P = 0.032), and a relative increase in subjective relaxation during the post-task recovery period (P = 0.036).
Conclusions Compared with placebo, 6 weeks of tea consumption leads to lower post-stress cortisol and greater subjective relaxation, together with reduced platelet activation. Black tea may have health benefits in part by aiding stress recovery

http://www.springerlink.com/content/m22 ... c2fec&pi=0
Listen to all,
plucking a feather from every passing goose,
but follow no one absolutely

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