Tea helps with stress relief
Drinking tea can help you recover more quickly from the stresses of everyday life, according to a new study by UCL (University College London) researchers. New scientific evidence shows that black tea has an effect on stress hormone levels in the body.
The study, published in the journal Psychopharmacology, found that people who drank tea were able to de-stress more quickly than those who drank a fake tea substitute. The study participants - who drank a black tea concoction four times a day for six weeks - were found to have lower levels of the stress hormone cortisol in their blood after a stressful event, compared with a control group who drank the placebo tea for the same period of time.
In the six week study, particpants gave up their normal tea, coffee and caffeinated beverages, then one group was given a fruit-flavoured caffeinated tea mixture made up of the constituents of an average cup of black tea whilst the control group was given a caffeinated placebo identical in taste. Both groups were subjected to challenging tasks, while their levels of stress were measured.
When measured both groups showed evidence of similar stress levels, however, 50 minutes after the task, cortisol levels had dropped by an average of 47 per cent in the tea drinking group compared with 27 per cent in the placebo tea group.
Reference: Psychopharmacology. 2006 Sep 30; (Epub ahead of print)
Steptoe A et al. The effects of tea on psychophysiological stress responsivity and post-stress recovery: a randomised double-blind trial
Polyphenols as prebiotics
'Good' bacteria have been popularised by the huge advertising campaigns for the plethora of dairy products that claim to enhance bowel health. However, not only the oral addition of said 'good' bacteria could increase the number of bacteria in the bowel. Prebiotics have received less attention than probiotics - they are found naturally in foods like bananas, artichokes and leeks and can be best described as 'food' for the probiotic or 'good' bacteria.
Tea is not normally described as a prebiotic, but microbiologists from the National University of Singapore have been examining the prebiotic effects of tea's polyphenols. Tea is commonly known to be a rich source of polyphenols, which are widely reported to have heart health promoting benefits. In this latest study, scientists looked at faecal levels of bacteria - both good and bad - and the influence tea polyphenols had on their growth.
Different bacteria responded differently in the presence of tea's polyphenols. The growth of certain harmful bacteria were generally suppressed while good, probiotic bacteria were less affected. The authors conclude that tea's polyphenols have a positive effect on the intestinal environment by acting as a metabolic prebiotic and they could have a role to play in maintaining intestinal health.
Reference: Res Microbiol. 2006 Aug 18; (Epub ahead of print)
Lee HC et al. Effect of tea phenolics and their aromatic fecal bacterial metabolites on intestinal microbiota.
Do tea flavonoids help reduce blood pressure?
The consumption of tea and particularly the flavonoids in tea have long been associated with improved heart health. Tea provides one of the most readily available sources of flavonoids, and in many cases, tea is the main contributor.
How flavonoids work to improve heart health has long been a contentious issue and a variety of mechanisms have been investigated. This latest review paper has examined the evidence to see if tea's flavonoids can help to lower blood pressure through endothelium function modification (endothelium cells are flat cells that line the internal surface of blood vessels).
The researchers found that in test tubes, tea's flavonoids had a dilatory effect on blood vessels (hence they make blood flow 'easier'), which can lead to a reduction in blood pressure. Measures of blood pressure, following the consumption of tea, on people with normal readings showed few positive indicators of a lowering effect, although some animal and population studies have been favourable.
The researchers conclude that the consensus suggests that the effects of tea on endothelial function, and thus perhaps blood pressure, could be one of the heart health benefits of drinking tea.
Reference: Clin Exp Pharmacol Physiol 2006 Sept; 33(9): 838-41
Hodgson JM. Effects of tea and tea flavonoids on endothelial function and blood pressure: a brief review.
Catechins exert significant antioxidant power and may prove to be important heart healthy agents in combating lipid peroxidation within cell membranes lining arterial walls and reducing formation of atherosclerotic plaque. In particular, the tea catechin, epigallocatechin gallate (EGCG), is currently being studied for its role as a chemoprotective agent. Scientists speculate that EGCG may be responsible for suppressing growth of tumors as well as inhibiting enzymes that are involved in spread of cancer cells.
In fact, what distinguishes EGCG from other compounds is that it seems to have a unique ability to fight cancer at all stages, from inhibiting development of tumors, to eradicating tumor promoters, blocking chemical carcinogens and neutralizing enzymes involved in cell proliferation. Current research has shown EGCG to be as much as 100 times more potent than vitamin C and 25 times more potent than vitamin E in antioxidant power. Antimicrobial properties in green tea are also attributed to EGCG, which has been shown to repress the growth of bacteria such as helicobacter pylori, E. coli, and Staphylococcus aureus. Scientists have not yet determined specific amounts of catechins needed to exert health benefits.
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