Instant tea may be a source of harmful levels of fluoride that can lead to bone pain, researchers discovered after they looked into the case of a woman who drank one to two gallons of super-strength tea daily.

Scientists say it's not the country's biggest dietary problem. But it does make the point "all things in moderation," said lead researcher Dr. Michael Whyte of the Washington University School of Medicine.

He said the study tested 10 brands of instant tea at regular-strength levels in fluoride-free water; they didn't test brewed or bottled tea. Fluoride levels ranged from 1.0 to 6.5 parts per million. The maximum level allowed in drinking water by the Environmental Protection Agency is 4 ppm.

Fluoride is absorbed naturally into tea plants from soil and rain water, and varies from "year to year, harvest to harvest and hill to hill ... and among regions of the world," Whyte said.

Swallowing high levels of fluoride boosts bone density, but also makes bones more brittle. It can lead to skeletal fluorosis, which causes bone pain, calcified ligaments, bone spurs, fused vertebrae and difficulty in moving joints. It's a rare condition in the United States, Whyte said, but in some countries is more common than osteoporosis.

He said regular consumers of high-fluoride brick tea made from old leaves, berries and plant twigs in parts of China and Tibet suffer aching, dense, poor-quality bones.

It was this rare condition that prompted the Washington University study. Scientists wanted to find the cause of a middle-aged woman's spinal pain. Tests revealed high levels of fluoride in her urine. She then disclosed she drank one to two gallons of double-strength instant tea each day.

Now she drinks lemonade. Although her fluoride levels are back to normal, her bone density remains high but her pain has eased.

Aside from pointing to the need to drink tea in moderation, the study suggests more research into tea's fluoride content is needed. The findings were in the January issue of the American Journal of Medicine.

Fluoride is added to most major cities' drinking water to help prevent tooth decay. A British analysis in 2000 of numerous fluoride studies found no increased risk of bone fractures among the elderly from adding fluoride to drinking water.

Joe Simrany, president of the Tea Association of the United States, said "drinking tea is an entirely safe proposition. You'd have to consume so much tea for it to become an issue."

Dr. Michael Kleerekoper, a professor of medicine at Wayne State University who conducted a five-year, nationwide study of fluoride treatment for osteoporosis in the 1980s, said Whyte's study shows that anything consumed to excess is not good, whether it's "four gallons of pop or two liters of whiskey."

"Of all the dietary excess in society today, this is probably not the biggest culprit," he said. "I'm not minimizing his work, but the problem is one of excess."

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On the Net:

The American Journal of Medicine: http://www.ajmselect.com/

Washington University School of Medicine: http://medicine.wustl.edu/

Tea Association of the United States: http://www.teausa.com/general/icedtea.cfm