Friday, September 29, 2006

The benefits of a good cuppa

The month of Ramadan can be a hard experience for the uninitiated but that is more than compensated for by the sense of purity, spirituality and morality. In any case the body adapts quickly and the two meals in 24 hours (or one in my case) is easily sufficient to maintain calorific supply. After breaking fast, a good cuppa is almost compulsory for recharging. This paper by a group in Perth looks at the effects of tea on fasting and post meal blood pressure:

Hodgson JM, Puddey IB Asia Pac J Clin Nutr. 2004;13(Suppl):S71. Background - Results of population and intervention studies suggest that drinking tea might protect against cardiovascular disease (CVD). However, tea contains caffeine, which can transiently increase blood pressure (BP) in people who have avoided caffeine for > 12h. We have previously shown that a single dose of tea (equivalent to 4 standard cups containing 180mg of caffeine) transiently increased BP more than caffeine alone (180mg dose) in people who had fasted and avoided caffeine for > 12h. The importance of this finding to risk of CVD is uncertain since short-term regular ingestion of tea does not alter BP, and results of population studies suggest that long-term regular ingestion of tea may lower BP. Objective - To investigate the acute effects of tea consumption with and without food on BP. Design - BP was measured in 20 participants with coronary artery disease before and 3.5h after drinking 3 cups of black tea or hot water with and without a meal. There were a total of 4 treatments (water alone, tea alone, meal with water and meal with tea) administered in random order. One cup of tea or water was provided at time=0, 1.5 and 3h. The meal was provided at time=0 and consumed over 0.5h. Outcomes - In comparison to water alone, tea alone significantly increased mean (95%CI) systolic BP by 9.4 (1.3, 17.5)mmHg (P=0.01). However, there was negation of the acute pressor effect of tea when the tea was consumed after a meal (2.2 (-5.9, 10.2) mm Hg;NS). Conclusions - A capacity for food to negate the pressor activity of tea in the fasting state may help to explain a lack of any longer-term effects to raise BP. The apparent inconsistency between the results from acute studies and studies of regular ingestion may be due to differential effects of tea, in the fasting and fed states, on BP. That is, people generally drink tea with and between meals rather than in a fasting state.

Another interesting paper compares the effect of green tea and black tea on metabolism:

J Hypertens.1999 Apr;17(4):457-63 Green and black tea consumption resulted in similar increases in urinary excretion of hippuric acid and 1,3-dihydroxyphenyl-2-O-sulfate, both of which are end products of tea flavonoid degradation by colonic bacteria. Several unidentified aromatic metabolites were detected in urine specifically after green tea intake. Interestingly, green and black tea intake also had a different impact on endogenous metabolites in urine and plasma. Green tea intake caused a stronger increase in urinary excretion of several citric acid cycle intermediates, which suggests an effect of green tea flavanols on human oxidative energy metabolism and/or biosynthetic pathways.

I think I would have quite enjoyed writing the materials and methods for this study as well as the actual experiment. Research is so much nicer when you can eat or drink the results.


Blogger Philip said...

And, of course, when you can impress your fellow scientists by peeing unidentified aromatic metabolites up the neighbours' wall.

7:57 PM  
Blogger Kebz said...

I prefer the lavatory Philip but it isn't unknown for scientists to do stuff like that. I knew a PhD student who took a dump in a rubbish bin located outside the front entrance of the building that I worked in. The security guards went to investigate but were unable to catch him in the act. I can't imagine what they would have done to stop him even if they had caught him.

8:07 PM  

Post a Comment

<< Home