Sites Grátis no Comunidades.net Criar um Site Grátis Fantástico
Does green tea extract caffeine*

The truth about green tea

It's the poster child for healthy foods, but Dr Karl reckons the best science can say about green tea is "mostly harmless"

Green tea is "mostly harmless" (Source: Beboy_ltd/iStockPhoto)

Related Stories

That lovely hot beverage, tea, is one of the most popular liquids regularly consumed by humans It can give you a "lift", without the edginess that sometimes accompanies a cup of coffee

There's one specific variety of tea called "green tea", for which many marvelous claims are made But not all green tea is what it's cracked up to be — and in some cases, it can harm you

There are a few different types of tea around Black tea is popular in Europe, North America and North Africa, and makes up about 80 per cent of all tea produced and consumed Green teas makes up most of the rest of the tea that's enjoyed, and it's widely drunk in China, Korea, Japan and Morocco Only very small quantities of white tea and oolong tea are drunk

The difference between green and black tea is firstly that they tend to come from different varieties of the tea plant, Camelia sinesis, and secondly, how they are processed

The green tea leaves do not go through an oxidising process, so the leaves contain so-called "non-oxidised phenolic compounds", such as catechins, and the teas are lighter in colour However, the black teas do go through an oxidising process, and so they contain "oxidised phenolic compounds" such as theaflavins and thearubigins, and the final liquid is darker in colour

So the dried leaves of each contain roughly the same levels of proteins and amino acids (about 19 per cent by weight), fibre and other carbohydrates (33 per cent), fats (7 per cent), pigments (2 per cent) and minerals (5 per cent) The difference is that green tea has no oxidised phenolic compounds, while black tea has about 25 per cent

You've heard of caffeine in coffee — an average cup has about 100 milligrams Black tea has about 55 mg of caffeine, while green tea has about 20 milligrams

But it's mostly the phenolic compounds that are claimed to be the basis of all those amazing health effects — a treatment for headaches, various body aches and pains, and depression, as well as a protector again cancers of the stomach, colon, breast, ovary, bladder and prostate And just to round things off, green tea is also claimed to protect against osteoporosis and dental caries

But then, many of these supposedly good chemicals are found in fruit and vegetables, and in cocoa and wine

But when you look closely at the studies, they are overwhelmingly not human studies — rather, they're mostly either animal studies or cell-line studies on the laboratory bench

Now about 80 per cent of the green tea is produced in China A study in 2006 measured lead levels in Chinese green teas It found that some of them were 50 times the maximum permitted level This lead contamination is due to China's massive industrialisation The lead is absorbed from the soil via the roots, or lands on the leaves from the local environment

Now some of the chemicals in green tea are quite powerful So looking not at liquid green tea, but rather at the green tea extract pills sold in health food shops, there are many cases of these pills causing liver damage and visible jaundice — requiring hospitalisation

Americans drink about 10 billion servings of green tea each year — in various forms In 2013, an independent tester of health products of all kinds, ComsumerLabcom, tested green teas

The pre-prepared bottled green tea beverages were mostly loaded with sugar and extra caffeine — and usually didn't carry the advertised quantities of good green tea chemicals as claimed on the label The chemical analyses of the loose leaf and tea bag versions of green tea were similar to the prepared beverages — but without the added sugar The surprise was that some of the tea bags delivered 25 micrograms of lead per serving

Now green tea was apparently first brewed way back some 28 centuries before Christ, in the reign of the Chinese Emperor Chen Nung — so it has a long history

Maybe the take home message is to sip it demurely, rather than guzzle down gallons

Published 05 March 2014

Use these social-bookmarking links to share The truth about green tea Casandra is multifaceted in the industry and is known for wearing many hats.

Use this form to email 'The truth about green tea ' to someone you know:

Subscribe to the Great Moments in Science Podcast

Latest Dr Karl's Great Moments In Science

You might also be interested in Diet and Nutrition

Follow ABC Science

About | Contact | ABC Science

Topics

Watch

More science sites

Related ABC sites

Search ABC Science

Stay updated

ABC Science Newsletter

Get ABC Science’s weekly newsletter Science Updates