Green tea, which has been consumed for more than 4,000 years, has been the focus of many health claims. The earliest recorded book extolling the virtues of green tea is the Kissa Yojoki (Book of Tea), which was published in 1191 by a Zen priest, Eisai. The first sentence of the book goes like this: “Tea is the ultimate mental and medical remedy and has the ability to make one’s life more full and complete.”
Eisai thought that the bitter taste of green tea would strengthen the heart and free the body from illness. He may have been on to something, but it would take almost 1,000 more years to find out the chemical properties of green tea, and the implications for health are still being worked out.
What’s in Green Tea: The first thing you should know is that green tea contains caffeine. How much? You may be surprised to learn that a cup of green tea brewed for 5 minutes will have nearly as much as a cup of freshly ground coffee – 32mg. ( Please note, however, that on average brewing times for green teas usually range from 2-3 minutes. ) The longer it’s brewed, the more caffeine will be released – a standard tea bag has about 50mg caffeine. The leaves also contain the caffeine metabolites theophylline and theobromine, which act much like caffeine but also have anti-asthma properties.
But most of the excitement about green tea comes from those bitter tasting compounds, which are collectively known as catechins. These flavonoids make up about 25% of the weight of a green tea leaf, although the exact proportion can vary by location and growing conditions. The most common catechin in green tea is epigallocatechin gallate (EGCG) and is a powerful antioxidant.
The idea that this compound can reduce inflammation has led to most of the health claims, real and otherwise. Although brewing the tea with water at 165°-175° (ideal brewing temperature for green tea) can damage the catechins, several have pointed out that this method has probably saved millions of lives over the years by killing the bacteria responsible for cholera and typhoid fever!
The Evidence: The health benefits of tea is such a big subject that there are multiple yearly scientific meetings. I can’t possibly cover all of the evidence but I will make a general statement and look at one study in particular. The statement is that the gold standard in clinical studies is the randomized, blinded, placebo-controlled trial – and there have been none of these published to back up the big claims. In fact, the FDA has rejected petitions to claim that green tea reduces the risk of cancer and the risk of heart disease.
The most interesting study published to date (JAMA, Sept 2006) followed a group of 40,530 Japanese adults for about a decade. 4,209 people died, and the authors determined that drinking green tea had a protective effect from overall death. Men who drank five or more cups per day had a 12% lower risk of dying, and women were even better off, with a 23% lower risk of dying.
These figures held up to statistical testing, although for the men the lower risk could be as low as 2%, statistically speaking. When the authors looked at subsets of the cohort (known as subgroup analysis) they couldn’t find any benefit in preventing cancer-related mortality, but they did find reduced death from cardiovascular causes, especially stroke, in the heavy drinking folks.
Future Studies: So now that the evidence is starting to build that green tea might protect people from dying, especially from cardiovascular disease, and stroke to be specific, what’s next? For starters, it would be nice to see the results of the Japanese study replicated in other parts of the world. There are currently 28 studies in the United States recruiting subjects to look at a variety of disease responses, from cancer to diabetes to osteoporosis, although most of these are small trials. In conclusion, Eisai could be right – drinking large quantities of green tea really might save your life. Stay tuned!