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For many, no drink is more synonymous with good health than green tea, the ancient Chinese beverage known for its soothing aroma and abundance of antioxidants. By some estimates, Americans drink nearly 10 billion servings of green tea each year.

But a new report by an independent laboratory shows that green tea can vary widely from one cup to the next. Some bottled varieties appear to be little more than sugar water, containing little of the antioxidants that have given the beverage its good name. And some green tea leaves, particularly those from China, are contaminated with lead, though the metal does not appear to leach out during the brewing process.

The report was published this week by ConsumerLab.com, an independent site that tests health products of all kinds. The company, which had previously tested a variety of green tea supplements typically found in health food stores, took a close look at brewed and bottled green tea products, a segment that has grown rapidly since the 1990s.

It found that green tea brewed from loose tea leaves was perhaps the best and most potent source of antioxidants like epigallocatechin gallate, or EGCG, though plain and simple tea bags made by Lipton and Bigelow were the most cost-efficient source. Green tea’s popularity has been fueled in part by a barrage of research linking EGCG to benefits like weight loss to cancer prevention, but the evidence comes largely from test tube studies, research on animals and large population studies, none of it very rigorous, and researchers could not rule out the contribution of other healthy behaviors that tend to cluster together.

Green tea is one of the most popular varieties of tea in the United States, second only to black tea, which is made from the leaves of the same plant. EGCG belongs to a group of antioxidant compounds called catechins that are also found in fruits, vegetables, wine and cocoa.

The new research was carried out in several phases. In one, researchers tested four brands of green tea beverages sold in stores. One variety, Diet Snapple Green Tea, contained almost no EGCG. Another bottled brand, Honest Tea’s Green Tea With Honey, claimed to carry 190 milligrams of catechins, but the report found that it contained only about 60 percent of that figure. The drink also contained 70 milligrams of caffeine, about two-thirds the amount in a regular cup of coffee, as well as 18 grams of sugar, about half the amount found in a can of Sprite.

Another phase of the study looked at green tea in its more natural forms – loose tea leaves sold by Teavana and tea bags sold by companies like Bigelow and Lipton. A single serving of Teavana’s Gyokuro green tea, about one teaspoonful, was chock-full of antioxidants, yielding about 250 milligrams of catechins, a third of which were EGCG. It also contained 86 milligrams of caffeine, slightly less than a regular cup of coffee.

A single bag of the green tea sold by Lipton and Bigelow contained somewhat smaller amounts of antioxidants than Teavana’s green tea and generally minimal amounts of caffeine. But Teavana’s recommended serving size was large, and the tea was also far more expensive, resulting in a higher cost per serving. The report calculated that the cost to obtain 200 milligrams of EGCG ranged from 27 cents to 60 cents with the tea bags, and $2.18 with the Teavana loose tea leaves.

But the most surprising phase of the study was an analysis of the lead content in the green tea leaves. The leaves in the Lipton and Bigelow tea bags contained 1.25 to 2.5 micrograms of lead per serving. The leaves from Teavana, however, did not contain measurable amounts.

“Lead can occur in many botanical products because it is taken up from the ground,” said Dr. Tod Cooperman, president of ConsumerLab.com. “The green tea plant is known to absorb lead at a higher rate than other plants from the environment, and lead also can build up on the surface of the leaves.”

Dr. Cooperman said the tea leaves containing lead probably originated in China, where studies have found that industrial pollution causes the leaves in some regions to gather substantial amounts of lead. The Teavana leaves came from Japan, where that is less of a problem, he said. The decaffeination process also helps remove lead.

Still, the study found that there was no real prospect of a health concern from the lead. The liquid portions of the teas that were brewed and tested contained very little if any of the metal, Dr. Cooperman said.

“The majority of the lead is staying with the leaf,” he said. “If you’re brewing it with a tea bag, the tea bag is very effectively filtering out most of the lead by keeping those tea leaves inside the bag. So it’s fine as long as you’re not eating the leaves.”