The U.S. government has decided to lower its recommended limits for fluoride in municipal water supplies -- the first such change in nearly 50 years -- as debate grow about the risks of too much fluoride.

The U.S. Department of Health and Human Services (HHS) proposed Friday that the recommended level of fluoride in drinking water be set at the lowest end of the current optimal range to prevent tooth decay.

The HSS says it wants to recommend that the fluoride level in municipal water supplies be lowered to 0.7 milligrams per litre of water. The standard since 1962 has been a range of 0.7 to 1.2 milligrams per litre.

The Environmental Protection Agency (EPA), meanwhile, announced Friday it is initiating a review of the maximum amount of fluoride allowed in drinking water.

Fluoride in drinking water has been credited with dramatically cutting cavities and tooth decay. Indeed, the joint HHS and EPA announcement notes that the Centers for Disease Control and Prevention named the fluoridation of drinking water as one of the 10 great public health achievements of the 20th century.

The problem is that children may now be getting too much of a good thing. Fluoridation critics note the rise in the prevalence of fluorosis, a dental condition in which a buildup of fluoride causes unsightly dark splotches on the teeth.

In most kids, fluorosis is barely noticeable; in rare, severe cases, the condition causes the teeth to actually become pitted and brown.

According to the CDC, nearly 23 per cent of U.S. children ages 12-15 had at least some degree of fluorosis in 1986 and 1987. That rose to 41 per cent in a more recent CDC study covering the years 1999 through 2004.

The Canadian Dental Association says dental fluorosis "is not an issue of concern for the vast majority of children" in Canada.

It cites the Health Measures Survey of 2007-2009 which found that just 16 per cent of Canadian children have mild forms of fluorosis that often go unnoticed by both the children and their parents.

Most communities in the U.S. have fluoride in their water supplies, as do many communities in Canada. But in recent years, a fluoride backlash has erupted among some who worry about the long-term effects of the mineral.

Other critics also worry whether the mineral can impede brain development in children, while still others are against fluoridation because they say it's unethical to distribute a substance to the masses without their full consent and infringes on their right to choose.

Voters in Waterloo, Ont. voted in a plebiscite last October to bring an end to the water fluoridation practice that had been in place in the community since 1967.

The vote was close, with the "No" side winning by just 195 votes out of almost 31,000. The fluoride taps were turned off at the end of November, with the region pledging to monitor the eventual impact on dental health.

A similar debate has erupted in Calgary. An alderman there has presented a motion calling for the city to scrap its fluoridation program. The city has held six plebiscites on the issue since 1957, finally deciding in 1989 to begin adding fluoride to the city's water supply, starting the program two years later.