The federal government lowered its recommended limit on the amount of fluoride in drinking water for the first time in nearly 50 years, saying that spots on some children’s teeth show they are getting too much of the mineral.
Fluoride has been added to U.S. water supplies since 1945 to prevent tooth decay. Since 1962, the government has recommended adding a range of 0.7 milligrams to 1.2 milligrams per liter.
But federal officials said Friday they would move the recommended limit to 0.7 milligrams per liter, or the bottom end of the current range, because people are getting more fluoride these days from other sources, such as toothpaste, mouthwash, prescription fluoride supplements, and fluoride treatments given by dentists.
A study conducted between 1999 and 2004 by the federal Centers for Disease Control and Prevention found that 41% of children between the ages of 12 and 15 exhibited signs of dental fluorosis, a spotting or streaking on the teeth. That was up from nearly 23% found in a study from 1986 and 1987.
The CDC believes the increase is due mostly to children swallowing toothpaste with fluoride when they brush their teeth.
The American Dental Association commended the new federal recommendations for preserving fluoridation.
“Water fluoridation is one of our most potent weapons in disease prevention,” ADA President Raymond F. Gist said in a statement.
Federal health officials have called fluoridation one of the 10 great public-health achievements of the 20th century, saying it significantly cuts the rate of cavities and saves money.
But for years, some groups have called for an end to fluoridation, arguing that it poses serious health dangers, including increased risk of bone fractures and of decreased thyroid function. Friday’s announcement did little to appease such critics.
“The only rational course of action is to stop water fluoridation,” said Paul Connett, executive director of the Fluoride Action Network, a nonprofit advocacy and fluoride-education group.
It isn’t clear how much change the new recommendations will bring. Cities and towns decide on their own how much fluoride to add to water, within the federal recommended range.
Many communities are already at the new recommended level, said Howard K. Koh, assistant secretary for health at the Department of Health and Human Services.
About 64% of the U.S. population has access to fluoridated water, according to the CDC.
Dental fluorosis can result when children ages eight and younger—their tooth-forming years—consume excess fluoride. The mineral causes the tooth enamel to become harder and more opaque, so the extra density makes light bounce off of it, causing spots or streaks.
The condition isn’t harmful and often is visible only to dentists. “In most cases, a non-dentist wouldn’t be able to see it,” said Matthew Messina, a dentist from Fairview Park, Ohio. “It doesn’t weaken teeth or anything like that.”
It doesn’t develop in adults because their enamels are fully developed. “Once the teeth are in your mouth, regardless of how much fluoride you take in, you’re not at risk,” said Scott Tomar, a professor at the University of Florida’s college of dentistry in Gainesville.
Not every dentist is seeing greater fluorosis. Bob Wilson, a dentist in Gaithersburg, Md., said instances of the condition have remained consistent in his 25 years. He encounters fewer than one case a week, he said.
“It’s just not a problem that we see very often,” he said.
Fluoride is a mineral occurring naturally in water and soil. The government began adding it to water after scientists found that people living in areas where the water supply had higher levels of naturally occurring fluoride also had fewer cavities.
Fluoride plays both offense and defense for the teeth. It makes teeth more resistant to acid, which creates holes where bacteria collect, leading to decay. Fluoride also regenerates weakened tooth enamel.
Bottled water contains small traces of fluoride but most is eliminated during the filtration process, said Andrea Foote, a spokeswoman for PepsiCo Inc., which owns Aquafina bottled water.
Despite fluoridation, government officials remain concerned about tooth decay, particularly in low-income populations. Tooth decay remains the most common chronic disease among children ages six to 19, according to the CDC.