The Ministry of Health and Welfare has authorized the addition of fluoride to public water supplies because the chemical helps fight tooth decay, officials said Friday.

They said that municipal governments, which are responsible for local water supply services, have already been informed of the change in government policy.

The move follows a request from a municipal government in Okinawa Prefecture, which had sought permission to add fluoride to its public water supply.

In accordance with the new policy, municipal governments will be allowed to add fluoride to their water supplies up to an officially standardized concentration, after obtaining the consent of local residents.

Currently, government regulations limit the quantity of fluoride in public water supplies to 0.8 parts per million, or 0.8 milligrams per liter, according to ministry officials.

Although the ministry has previously officially acknowledged that fluoride is effective in the prevention of tooth decay, it had refrained from allowing it to be added to public water supplies because of concerns about an adverse effect on health, including causing cancer.

About 80 percent of the toothpaste sold in Japan contains fluoride.

However, fluorides can also cause speckling of the teeth if frequently used in concentrations of more than 2 ppm. Using fluoride at more than 8 ppm could trigger sclerosis of the bone, according to ministry officials.

In 1969, the World Health Organization adopted a resolution to promote the use of fluoride in public drinking water supplies.

Currently, at least 38 nations use fluoridated public water supplies as a means of preventing tooth decay, ministry officials said.

The United States has authorized the addition of fluoride to public water supplies since 1945.

About 60 percent of the U.S. population now have fluoridated water coming out of their taps.

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