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 kids’ teeth.

A reported increase in the spotting problem is one reason the federal government will announce Friday 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.

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

The U.S. Department of Health and Human Services is announcing 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 kids ages 12 through 15. And it appears to have grown much more common since the 1980s.