ATLANTA — Fluoride in drinking water — credited with dramatically cutting cavities and tooth decay — may now be too much of a good thing. Getting too much of it causes spots on some children’s teeth.

A reported increase in the spotting problem is one reason the federal government announced yesterday that it plans to lower the recommended levels for fluoride in water supplies — the first such change in nearly 50 years.

About 2 out of 5 adolescents have tooth streaking or spottiness because of too much fluoride, a surprising government study found recently. In some extreme cases, teeth can even be pitted by the mineral — though many cases are so mild only dentists notice it. The problem is generally considered cosmetic.

Health officials note that most communities have fluoride in their water supplies, and toothpaste has it too. Some children are even given fluoride supplements.

The US Department of Health and Human Services announced a proposal to change the recommended fluoride level to 0.7 milligrams per liter of water. And the Environmental Protection Agency will review whether the maximum cutoff of 4 milligrams per liter is too high.

The standard since 1962 has been a range of 0.7 to 1.2 milligrams per liter.

The Centers for Disease Control and Prevention reports that the splotchy tooth condition, fluorosis, is unexpectedly common in children ages 12 through 15. And it appears to have grown much more common since the 1980s.

But there are other concerns, too. A scientific report five years ago said that people who consume a lifetime of too much fluoride — an amount over EPA’s limit of 4 milligrams — can lead to crippling bone abnormalities and brittleness.

That and other research issued yesterday by the EPA about health effects of fluoride are sure to reenergize groups that still oppose adding it to water supplies.

The American Dental Association released a statement applauding the government announcement to change fluoride guidance.

Portland, Ore., is one of the largest cities that doesn’t fluoridate its water. Bill Zepp of the Oregon Dental Association said the city’s antifluoridation activists will embrace the recommended fluoride changes “as some type of win.’’

Maryland is the most fluoridated state, with nearly every resident on a fluoridated system. In contrast, only about 11 percent of Hawaii residents are on fluoridated water, according to government statistics.

Fluoridation has been fought for decades by people who worried about its effects, including conspiracy theorists who thought it was a plot to make people submissive to government power.

Those battles continue.

“It’s amazing that people have been so convinced that this is an OK thing to do,’’ Deborah Catrow said yesterday. She successfully fought a ballot proposal in 2005 that would have added fluoride to drinking water in Springfield, Ohio.

Reducing fluoride would be a good start, but she hopes it will be eliminated altogether from municipal water supplies.

Catrow said it was hard standing up to City Hall, the American Dental Association, and the state health department. “Anybody who was antifluoride was considered crazy at the time,’’ she said.

In New York, the village of Cobleskill in Schoharie County — west of Albany — stopped adding fluoride to its drinking water in 2007 after the longtime water superintendent became convinced the additive was contributing to his knee problems. Two years later, the village reversed the move after dentists and doctors complained.

In March, 2006, the National Academy of Sciences released a report recommending that the EPA lower its maximum standard for fluoride in drinking water to below 4 milligrams. The report warned severe fluorosis could occur at 2 milligrams. Also, a majority of the report’s authors said a lifetime of drinking water with fluoride at 4 milligrams or higher could raise the risk of broken bones.

Late last year, lawyers for the Fluoride Action Network, Beyond Pesticides, and Environmental Working Group threatened legal action if the EPA did not lower its ceiling on fluoride.

© Copyright 2011 Globe Newspaper Company.