FLUORIDE IN THE UNITED STATES
When fluoride enters the mouth via drinking water, toothpaste,
or fluoride treatments, saliva concentrations of fluoride increase by 100- to 1,000-fold for
approximately one to two hours. During this time, the mouth is exposed to high concentrations
of fluoride, allowing it to exert its beneficial effects on the teeth, plaque, and bacteria.
Additionally, when fluoride is brushed onto the teeth via toothpaste, some fluoride is
directly absorbed by dental plaque [4].
FLUORIDE IN THE UNITED STATES
For many years, the recommended content of fluoride in U.S.
drinking water was 0.7–1.2 mg/L. In 2015, the U.S. Public Health Service (USPHS) simplified
this recommendation to provide an "optimal" level for fluoride in water: 0.7 mg/L (or 1 part
per million). This optimal level was identified as the fluoride concentration that would
maximize dental health benefits while minimizing risks, such as dental fluorosis [7].
Brewed teas present the most significant sources of fluoride in
the diet, even when the tea is brewed with non-fluoridated water. Depending on the type of tea
and the source of the tea leaves, a cup of tea made with non-fluoridated water can contain
between 0.3–6.5 mg/L of fluoride (or about 0.07–1.5 mg per cup of tea). Coffee can also
provide a notable amount of fluoride, depending on how the beans were prepared and where they
were grown; one cup of brewed coffee can provide around 0.22 mg fluoride [10].
Without appropriate precautions, formula-fed infants may be
at risk of elevated fluoride exposure. The fluoride content of infant formula depends
primarily on the water used for reconstitution. The CDC recommends that parents living in
areas with fluoridated water consider using bottled water labeled as deionized, purified,
demineralized, or distilled to reconstitute infant formula. Alternatively, ready-to-feed
formulas contain only small quantities of fluoride [13].
Urinary fluoride levels, while popular in epidemiological
research, are considered a potentially unreliable marker of fluoride intake. These levels
can be altered by various factors, including individual variability in fluoride
pharmacokinetics, lifestyle factors (e.g., smoking and alcohol consumption), and
intermittently elevated intake from fluoride-containing dental products or high-fluoride
foods [14]. Additionally, one study
investigating the impact of diet on urinary fluoride levels during pregnancy identified
variations between trimesters and between the pre- and postpartum states [15]. As a result, using urinary fluoride levels
as a marker of typical and long-term fluoride intake may lead to inappropriate
conclusions.
ASSESSING THE RISKS OF FLUORIDE
One exception to this rule is dental fluorosis. As the name
may imply, fluorosis is a known and established risk with fluoride exposure, and dental
fluorosis can occur in regions with fluoridated water. However, as with all other
fluoride-related risks, fluorosis only occurs with elevated exposure, and the degree of
severity is dose-dependent.
ASSESSING THE RISKS OF FLUORIDE
Dental fluorosis is caused by exposure to fluoride while
the teeth are still developing, a period that typically ends around 8 years of age.
Although the actual pathology of fluorosis is not fully understood, the uptake of large
quantities of fluoride by the enamel can lead to the development of white streaks or spots
on the teeth [16].
ASSESSING THE RISKS OF FLUORIDE
Multiple committees and agencies, including the National
Research Council (NRC), California's Carcinogen Identification Committee, the United
Kingdom's National Health Service (NHS), and the USPHS, have conducted independent reviews
that have all reached similar conclusions: There is no strong evidence of any link between
water fluoridation and cancer [18].
ASSESSING THE RISKS OF FLUORIDE
A meta-analysis of observational studies, mostly in children
6 to 18 years of age, has found that water fluoride is directly associated with thyroid
stimulating hormone (TSH) levels only at fluoride levels above 2.5 mg/L. There were no
consistent correlations between thyroid hormone levels (such as T3 and T4) and fluoride
exposure [28].
