May 15 (Reuters) - Florida on Thursday became the second

U.S. state to prohibit fluoride, a mineral used for decades to

protect teeth from decay, in its water systems.

The move is part of a broader push by U.S. Department of

Health and Human Services Secretary Robert F. Kennedy Jr. and

conservatives across the country to ban the use of the mineral,

which strengthens tooth enamel and promotes dental health.

In March, Utah became the first U.S. state to ban fluoride in

water supplies. The Food and Drug Administration said this week

it was starting a process to remove fluoride supplements for

children from the market.

Here is what you need to know about fluoridation of

drinking water as a public health measure:

WHAT IS FLUORIDE AND WHAT ARE ITS BENEFITS?

Fluoride, a mineral that occurs naturally in water, soil and

air, has been shown to prevent dental cavities, or tooth decay.

It works by strengthening the tooth's enamel, its hard outer

surface, making it more resistant to the acid produced by

bacteria that cause tooth decay. Fluoride also reverses early

tooth decay by replacing and preventing loss of minerals in

teeth.

Before community water fluoridation, tooth decay was

widespread and severe among Americans. After fluoride was added

to the water supply in many places in the U.S., tooth decay

declined in both children and adults, and complete tooth loss in

older adults became more rare, according to federal health

officials.

WHEN DID WATER FLUORIDATION AS A POLICY BEGIN?

In the early 20th century, some U.S. researchers observed

that people in areas where the community water supplies were

naturally high in fluoride had teeth that were resistant to

decay.

In 1945, Grand Rapids, Michigan became the first U.S. city to

add fluoride to its water supply in a controlled manner, kicking

off what was in effect a large-scale public health experiment.

Data over a 15-year span showed a reduction of more than 60% in

tooth decay among 30,000 school children in Grand Rapids,

demonstrating fluoride's protective benefits.

By the 1950s, the U.S. government's Public Health Service

and the American Dental Association acknowledged the success of

water fluoridation in reducing cavities. That led to the broad

U.S. adoption of adding fluoride in community water supplies and

eventually its inclusion in dental products such as toothpaste

and mouthwash.

No federal law mandates fluoridation of water supplies. The

decision to fluoridate water is typically made by municipal

governments, city councils or local water authorities.

HOW WIDESPREAD IS FLUORIDATION IN THE U.S.?

About 63% of all Americans have fluoride in their community

water systems as of 2022, according to the U.S. Centers for

Disease Control and Prevention.

The average cost per year for U.S. communities to fluoridate

their water supplies ranges from 50 cents per person for large

communities to $3 per person for small communities, according to

the American Dental Association.

In most of the world, fluoride is not added to the public

water supply. Some countries add fluoride to table salt. In some

regions, fluoride levels in water are naturally high.

ARE FLUORIDE LEVELS REGULATED?

The U.S. Public Health Service recommends that drinking

water levels for fluoride remain below 0.7 milligrams per liter.

Levels above 1.5 mg/l are known to increase health risks such as

bone fractures, thyroid disease and nervous system damage.

The enforceable limit as set by the U.S. Environmental

Protection Agency is 4.0 mg/l. A federal judge in California

recently ordered the EPA to strengthen its regulations.

WHAT COMPANIES MAKE FLUORIDE?

Fluorosilicic acid is the compound most widely used in water

systems as it yields free fluoride rapidly when mixed with

water. J.R. Simplot and Nutrien's ( NTR ) PCS Phosphate Co are

among companies that manufacture the product, according to the

EPA.

Total U.S. domestic production of fluorosilicic acid from

phosphate rock was about 29 million kilograms (32,000 tons) in

2019, according to EPA statistics.

WHAT HAS KENNEDY SAID ABOUT FLUORIDE?

The U.S. health secretary has claimed, without conclusive

evidence, that water fluoridation at U.S. levels is associated

with numerous health issues including cancer.

WHAT DO PUBLIC HEALTH EXPERTS SAY?

The CDC has called fluoridation of drinking water one of the

nation's top 10 public health achievements of the 20th century,

noting that it effectively prevents tooth decay regardless of a

person's socioeconomic status or access to care.

The American Dental Association has reiterated its support for

community water fluoridation to help prevent tooth decay.

Studies show that community water fluoridation reduces tooth

decay by more than 25% in children and adults even in an era

with widespread availability of fluoride from other sources such

as toothpaste, the association said.

WHAT QUESTIONS DO RECENT STUDIES RAISE ABOUT FLUORIDE?

A review published in October 2024 by the Cochrane Database of

Systematic Reviews raised questions about the value of

fluoridation of public drinking water in wealthy countries based

on the findings of 157 studies.

The research suggests that given the widespread addition of

fluoride to toothpaste since 1975, community water fluoridation

may now have only modest benefits in reducing tooth decay and

increasing cavity-free children, compared with the effects seen

in earlier studies. New lawsuits, however, are challenging

manufacturers on the safety of fluoride levels in toothpaste,

too.

The review also found there is not enough evidence to

determine the impact of stopping fluoridation or its effect on

socioeconomic disparities in dental health.

In January, researchers at the U.S. National Institutes of

Health who analyzed 74 studies from 10 countries found IQs were

lower in children with higher fluoride exposure. In four studies

with a low risk of bias involving 4,179 children, urinary

fluoride concentrations at levels reportedly common in developed

countries were associated with lower IQ scores, the researchers

reported.

The results "support concerns for vulnerable populations living

in communities with fluoridated water," according to an

editorial published with the report. A second editorial,

however, details multiple weaknesses of the NIH analyses and

warns that public policy concerning fluoride "should not be

affected by the study findings."

(Compiled by Reuters staff; Editing by Nancy Lapid and Bill

Berkrot)