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I've always been a bit of a 'tea pot' and can happily drink tea all day long. So when I received the two latest Arbor Clinical Nutrition Updates, I was pleased to read that my habit may be highly protective.
It's well known that black and green tea have been enjoyed in the East for many centuries and that Chinese and Japanese tradition attributes many healing properties to this beverage. Now, scientific studies from around the world are starting to identify just how beneficial that 'cuppa tea' may be.
Black vs. green
Tea, which is made from the leaves of the Camellia sinensis plant, is classified as green or black tea. To clarify these two concepts one needs to keep in mind that green tea is unfermented, oolong tea is partly fermented and black or red tea is fully fermented (Arbor, 2008A).
Note that in South Africa, black tea is traditionally referred to as 'Ceylon tea', despite the fact that tea is grown all over the world, including in our own country. This tradition may stem from the time when the Cape was governed by the Dutch East India Company and all the imported tea came from Ceylon.
When green tea leaves are fermented, the process causes changes in the composition of the tea by converting and reducing the concentration of chemical compounds called catechins in black tea (Arbor, 200A). Green tea, therefore, contains higher levels of these catechins, which are some of the substances that are believed to be beneficial.
The magic ingredients
Both black and green tea contain a number of chemical compounds that have potentially protective effects. The following compounds may play a role in tea’s health-giving properties:
- Catechins, a group of so-called polyphenols (polyphenols are potent antioxidants which are also found in red wine and unsifted grains). Catechins are responsible for the astringent taste that characterises black and green tea, and may constitute up to 33% of the dry weight of the tea. The most important catechin in tea is called epigallocatechin gallate. (Arbor, 2008 A)
- Other flavonoids or plant compounds that also have protective effects.
- Minerals, such as manganese.
- Caffeine, which acts as a stimulant and a mild diuretic. When used in moderation, caffeine should not cause insomnia or jitteriness. Excessive intakes can lead to restlessness, problems with sleeping and irritability.
Health benefits
According to the Arbor Clinical Nutrition Updates (Arbor, 2008 A & B), recent research has identified the following potentially important health benefits associated with drinking green and/or black tea:
- Green tea intake reduced the risk of breast cancer in a Chinese study.
- Use of epigallocatechin gallate, extracted from tea, reduced the growth of cervix cancer cells in a laboratory study.
- An extract of catechins obtained from green tea reduced the incidence of prostate cancer in a group of Italian men by 26,7% compared to men receiving placebo.
- A Japanese study found that five cups of green tea a day reduced the risk of men developing advanced prostate cancer by 50%, compared to having only one cup of green day daily.
- In an Australian study, drinking tea was associated with a 2,8% higher bone-mineral density in older women. The women who drank tea also lost less bone density (1,6%) than non-tea drinkers (loss of 4,0%) over a period of four years. Drinking tea may thus protect against osteoporosis.
- Although subjects who took green tea catechin capsules (equal to drinking six to seven cups of green tea per day) had similar blood-fat levels, one component that affects heart disease (plasma oxidised-LDL) was significantly lower than in control subjects.
- Green tea catechins also appear to have a weight-reducing effect and commercial products are already available for slimming purposes (Arbor, 2008 A & B).
Where do we stand?
In view of the above-mentioned research results, it's clear that drinking green and/or black tea or taking extracts of catechins may have many health benefits.
At this moment in time, however, tea research is still in the early stages and for every study that produces positive results, there are other studies that find no effect. To draw final conclusions about the benefits of tea, we require additional, large and well-controlled research studies to produce what is called ‘evidence-based’ results.
However, until we have this type of evidence, there is no harm in having tea (green or black) on a daily basis.
My favourite study
My family has always had the saying, 'Have a cup of tea before you die!' that came from a play my parents saw years ago. The implication that drinking a reviving cup of tea will make life less stressed, has now been proven by scientific research. Needless to say, this study was conducted by British researchers – the UK being the stronghold of tea drinking in the West.
After a tea- and caffeine-free period, 75 healthy men took a powdered extract equivalent to four cups of strong, black tea, every day for six weeks. The men were then made to do a number of stressful tasks. The physiological markers of stress that occur in the body such as platelet aggregation (increased sticking together of the platelets in the blood), cortisol production (a stress hormone made in the adrenal glands) and C-reactive protein were all lower in the subjects who took the tea extract than in the control subjects.
In addition, the men taking tea extract reported that they were significantly more relaxed after doing the stressful tasks. In other words, these men were more relaxed after being stressed than those who did not take tea extract – something that I too have often experienced.
Drinking tea is, therefore, an excellent way of relaxing and refreshing the body, and it may also have many other protective effects.
References:
(Arbor (2008A). Tea & Health - Part 1. Arbor Clinical Nutrition Updates, Edition 290, March 2008; Arbor (2008B). Tea & Health - Part 2. Arbor Clinical Nutrition Updates, Edition 291, April 2008.)
