TEA & HEALTH BENEFITS: TWO RECENT STUDIES*
In my September 2007 newsletter ‘A Cup of Tea = A Cup of Good Health’, it was shown that tea consumption (especially green tea) is linked to numerous positive effects on the body, in particular reducing mortality due to cardiovascular disease. Support for this came, for example, from a study of 40,000 adults which was published in the Journal of the American Medical Association in September 2006.
In the same newsletter, it was also documented that the consumption of green tea is associated with a lower prevalence of cognitive impairment in humans (American Journal of Clinical Nutrition, February 2006)
Two recent studies have lent further support to the claims that drinking tea is beneficial to the heart and cardiovascular system, as well as preventing or delaying cognitive decline.
A recent publication (June 2008) in the European Journal of Cardiovascular Prevention and Rehabilitation (15(3):300-305) looked at the acute effects of green tea consumption on endothelial function in healthy individuals.
It is accepted that green tea consumption is associated with decreased cardiovascular risk and death.
Flow-mediated dilation (FMD) of the brachial artery is related to coronary endothelial (the inner lining of the coronary arteries) function and is an independent predictor of cardiovascular risk. Although it has been shown that black tea has a beneficial effect on endothelial function, the effect of green tea had not been studied.
Design and Methods
14 healthy individuals (average age 30 years) with no cardiovascular risk factors were studied on three separate occasions. On each occasion, they took (the intervention) one ofThe FMD of the brachial artery was measured before each intervention and at 30, 90 and 120 minutes afterwards. As well as the FMD, other measures such as C- reactive protein (a protein produced as part of the inflammatory process and a routine test for heart failure), interleukins (the function of the immune system depends in large part on interleukins) and measures of plasma oxidative stress were carried out at baseline and at 120 minutes after each intervention.
6g of green tea
125mg of caffeine (the amount contained in 6g of tea)
Resting and hyperaemic brachial artery diameter did not change either with green tea or caffeine.
FMD increased significantly with the green tea. The increase was by 3.69%, peak at 30 minutes, p less than 0.02. It did not change significantly with caffeine (increase by 1.72%, peak at 30 minutes, p not significant).
Neither green tea nor caffeine had any effect on the other substances measured, as listed above.
“Green tea consumption has an acute beneficial effect on endothelial function, assessed with flow-mediated dilation (FMD) of the brachial artery, in healthy individuals. This may be involved in the beneficial effect of tea on cardiovascular risk.”
This study was published in the American Journal of Clinical Nutrition, Volume 88, No. 1, 224-231, in July 2008.
Laboratory research in animals has suggested that tea has potential neuro-protective effects. In other words, tea had been shown to delay or prevent cognitive impairment or deterioration of memory in animals. According to the authors, this neuro-protective effect had not been established in humans.
The objective of this present study was to examine the relation between tea intake and cognitive impairment and decline in humans.
Design and Methods
The researchers studied over 2,500 community-living Chinese in Singapore. They were all 55 years of age or older. The tea consumption was measured at baseline and memory tests were administered at baseline and 1-2 years later. The memory test was the Mini-Mental State Examination (MMSE).
Cognitive impairment was defined as an MMSE score of 23 or less and cognitive decline as a drop in MMSE score of 1 or more points.
Total tea intake was significantly associated with a lower prevalence of cognitive impairment, independent of other risk factors. Statistical calculations looked at the ‘Odds Ratios’ (OR’s) of association in logistic regression models that adjusted for potential confounders. For cognitive impairment, when the OR’s of rare or no tea intake were compared to the OR’s for low, medium and high levels of tea intake, the results were 0.56, 0.45 and 0.37 respectively (p for the trend was less than 0.001). For cognitive decline, the corresponding OR’s were 0.74, 0.78 and 0.57 (p for the trend = 0.042).
The authors found that these effects were most evident for black (fermented) and oolong (semi fermented) teas, the predominant types consumed by this population.
In contrast, no association between coffee intake and cognitive status was found.
“Regular tea consumption was associated with lower risks of cognitive impairment and decline.”
A few cups of green tea each day may help prevent heart disease. Green tea improves both blood flow and the ability of the arteries to relax. As my September 2007 newsletter on tea points out, other studies have shown that black tea has benefits for cardiovascular health. However, since green tea has higher quantities of the beneficial compounds called flavonoids, some of which are lost in the oxidation process that black tea undergoes, green tea would be the tea of choice to help prevent heart disease.
The second study above confirms in humans the neuro-cognitive protective effects of tea suggested in laboratory research. The results found that tea slows down brain-cell degeneration, and thereby keeps your mind sharp into old age. The catechins in the tea protect brain cells from damaging protein build-up over the years, maintaining your brain’s cognitive capacity. The statistics show that two-thirds of the tea-drinkers maintained their memory test scores two years later, compared to only one-third of non tea-drinkers.
‘p’ is a statistical way of indicating how likely the results could occur by chance (indicating the reliability of the data). The smaller the p, the more reliable the results are. For example 0.001 means that the result occurring by chance is 1 in 1000.
* Copyright 2008: The Huntly Centre.
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