HOLLADAY — The U.S. Department of Health and Human Services announced plans Friday to lower the recommended level of fluoride in drinking water for the first time in nearly 50 years, based on a fresh review of the science.

After decades of convincing local health authorities to fluoridate water, federal health officials now say many Americans are getting too much fluoride, and it's causing fluorosis — splotches on children's teeth — and perhaps other, more serious problems.

Salt Lake County, which started to fluroidate water in 2003, has already lowered the fluoride level for its water systems in anticipation of the federal recommendation. The changes won't affect other counties and water systems statewide that do not fluoridate water.

Holladay dentist Tony Tidwell said the new level will still reduce tooth decay, but minimize fluorosis.

"We're reducing it down because they found that the effectiveness is still good at a lower level," he said.

But the government's announcement may renew the battle over fluoridation, even though the addition of fluoride to drinking water is considered one of the greatest public health successes of the 20th century. In the United States, the prevalence of decay in at least one tooth among teens has declined from about 90 percent to 60 percent.

"Since we have put fluoride in the water, the number of cavities have dropped," Tidwell said.

One reason behind the government's recommended change: About 2 out of 5 adolescents have tooth streaking or spottiness because of too much fluoride, a government study found recently. In extreme cases, teeth can be pitted by the mineral — though many cases are so mild only dentists notice it. The problem is generally considered cosmetic and not a reason for serious concern.

The splotchy tooth condition, fluorosis, is unexpectedly common in youngsters ages 12 through 15 and appears to have grown more common since the 1980s, according to the Centers for Disease Control and Prevention.

Tidwell said fluorosis is not common in Utah.

"Once in a while, especially when parents are giving their children fluoride tablets, and the child's drinking the water at the same time, they can get too much," Tidwell said.

But there are also growing worries about more serious dangers from fluoride.

The Environmental Protection Agency released two new reviews of research on fluoride Friday. One of the studies found that prolonged, high intake of fluoride can increase the risk of brittle bones, fractures and crippling bone abnormalities.

The government proposal would 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.

Fluoride is a mineral that exists in water and soil. About 70 years ago, scientists discovered that people whose supplies naturally had more fluoride also had fewer cavities.

In 1945, Grand Rapids, Mich., became the world's first city to add fluoride to its drinking water. Six years later a study found a dramatic decline in tooth decay among children there, and the surgeon general endorsed water fluoridation.

And in 1955, Procter & Gamble Co. marketed the first fluoride toothpaste, Crest, with the slogan "Look, Mom, no cavities!"

But that same year, The New York Times called fluoridation of public water one of the country's "fiercest controversies."

The story said some opponents called the campaign for fluoridation "the work of Communists who want to soften the brains of the American people."

In 2000, Utah voters in elected to add fluoride to drinking water. The Utah Legislature later passed a bill that allows local residents to put fluoridation on the ballot every four years. The CDC has an online listing of which Utah water systems are fluoridated

The battles over fluoride continue in other locales around the country for a variety of reasons today.

In New York, the village of Cobleskill outside 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.

According to a recent CDC report, nearly 23 percent of children ages 12 to 15 had fluorosis in a study done in 1986-87. That rose to 41 percent in a study that covered 1999 through 2004.

"The report of discoloration has been going up over the years," said Dr. Robert Barsley, a professor at the LSU Health Sciences Center School of Dentistry. "It is not the water that's causing this by any means. It's the extra fluoride products — toothpaste, mouthwash — that people are using. And people want nice white teeth so they brush three times a day."

Susan Jeansonne, oral health program manager for Louisiana Department of Health and Hospitals, said one reason for the problem is children swallowing fluoride toothpaste or eating it.

Toothpaste labels have long recommended that parents supervise children under 6 when they are brushing their teeth; give them only a pea-size amount; and make sure they spit it out. Toddlers under 2 shouldn't use toothpaste with fluoride.

In 2006, the National Academy of Sciences released a report recommending that the EPA lower its maximum allowable level of fluoride in drinking water.

The report warned severe fluorosis could occur at 2 parts per million. Also, a majority of the report's authors said a lifetime of drinking water with fluoride at 4 parts per million or higher could raise the risk of broken bones.