Possibly one of the most widely studied natural substances in medical science - what exactly does green tea do?

Green tea is almost always in the news somewhere, usually because of suggestions that it may help prevent cancer, obesity, or cardiovascular conditions, or because it might reduce the  inflammatory effects of autoimmune diseases.  A quick search on PubMed- the online scientific studies database of the National Library of Medicine and the National Institutes of Health in the United States, reveals more than 2000 studies on the health effects of green tea. So I thought it might be an idea to take a look at some of the most recent data and expert opinion, in an effort to get an idea of what exactly green tea does do, besides quench your thirst.

Green tea is made from dried Camellia sinensis leaves. The Camellia sinensis is an evergreen shrub native to Southeast Asia. There is some evidence from studies done in populations living in Asia that consume green tea on a regular basis, that it confers benefit in terms of physical health. For example, in 2006 a large study done in 40,000 Japanese people showed that the more green tea the study participants consumed the longer they lived. Also, the incidence of cardiovascular disease was significantly reduced in people who drank five or more cups of green tea a day.

Green tea contains, among other things, polyphenols- and one in particular pigallocatechin-3-gallate (EGCG) – not only has strong antioxidant activity, but also appears to suppress inflammation. EGCG is of particular interest to medical researchers because inflammation occurs in many types of chronic illnesses– specifically autoimmune diseases such as rheumatoid arthritis (RA), psoriasis, lupus, and scleroderma. In a recent, early stage study from the University of Michigan Health System, (2007) researchers found that EGCG could provide therapeutic benefits to people with rheumatoid arthritis. In their study, EGCG inhibited the production of several molecules in the immune system that contribute to inflammation and joint damage in people with RA. The researchers also found that EGCG suppressed the inflammatory products in connective tissue of people with RA. Another recent study, by Dr. Stephen Hsu– a researcher in the Medical College of Georgia School of Dentistry, found that the EGCG administered in a green tea extract appears to help suppress inflammation in patients with dry mouth – also known as Sjorgen’s Syndrome – which is another auto-immune disease. In fact, their data showed that the group who were taking the green tea extract had significantly less damage to their saliva glands over time, compared to those were not taking the extract. Now this is not to say that the same results can be achieved by drinking green tea – but this study and the study done in patients with RA hint at some of the potential medicinal uses for the anti inflammatory properties of green tea.

There is also a large body of evidence to suggest that green tea may provide benefit in certain types of cancer – specifically breast, prostate, skin, stomach, and lung cancers. But to-date, there is insufficient clinical evidence – or data from well designed clinical trials in humans – to show that green tea categorically helps fight cancer. The same has to be said for cardiovascular disease, although all the evidence points to benefits rather than bad effects.

And that is, I discovered, the key point with green tea –no matter what type of chronic illness we’re talking about, overall, the evidence suggests that green tea has properties that help maintain good health, reduce inflammation, protect the heart and vasculature, and potentially inhibit the growth of cancers.

As for expert opinion – I think the Mayo Clinic sums up the current evidence best in their “Book of Alternative Medicine”(2007). They give green tea a “green light,” stating that “although the benefits of green tea have yet to be proved….. it does appear to have some medicinal qualities and it doesn’t pose serious side effects. Drinking green tea possibly may help reduce the risk of various cancers. It’s also linked to lower blood cholesterol and triglycerides……”

So, all the indicators are good. There’s just one important caution –if you are currently taking prescription medications for an illness such heart disease, diabetes, depression, cancer, Human Immunodeficiency Virus, or any ongoing condition – talk to your doctor before drinking green tea or taking any related supplements as a medicinal aid. It is possible that the tea could affect the drugs in a negative way, which could have possibly negative, long-term consequences.

Oh yes – I nearly forgot – green tea and weight loss. Well, again, there’s not a lot of good data in humans to show that drinking green tea or taking supplements containing green tea will help you lose weight. That’s not to say that green tea doesn’t help– just that it has yet to be definitively proved.

And this brings us to the subject of diet supplements. I would like to stress the need for caution and skepticism, especially concerning supplements that supposedly contain green tea extract for weight loss. With many over the counter diet supplements – and particularly those ordered online – it is very hard to tell what the ingredients are, where they come from, or how good a quality they are.  In other words – quality control is an issue. And, as we’ve seen very recently with toothpaste manufactured in China and India – some of the ingredients may be switched for less expensive –and potentially dangerous substances.  In April of this year I wrote a column on using weight loss products –things to look for when purchasing health supplements, with some very useful tips from Health Canada. You can access the column here: http://knowitallhealth.com/2007/04/19/using-health-products-for-weight-loss-safely/

Just for the record, I drink green tea on a regular basis and I can’t say it’s done me any harm. If nothing else, it really does quench my thirst and it doesn’t have any calories. And, regardless of all research on the health effects of green tea –it’s a very pleasant drink, which seems a pretty good reason to indulge.

Cheers! 

If you have a comment or question contact claire@knowitallhealth.com

Reviewed July 30th, 2007