June 29, 2015
If you’re like two-thirds of Americans,
fluoride is added to your tap water for the purpose of reducing
cavities. But the scientific rationale for putting it there may be
outdated, and no longer as clear-cut as was once thought.
Water fluoridation, which first began in 1945 in Grand
Rapids, Michigan, and expanded nationwide over the years, has always
been controversial. Those opposed to the process have argued—and a
growing number of studies have suggested—that the chemical may present a
number of health risks, for example interfering with the endocrine system and increasing the risk of impaired brain function; two studies in the last few months, for example, have linked fluoridation to ADHD and underactive thyroid.
Others argue against water fluoridation on ethical grounds, saying the
process forces people to consume a substance they may not know is
there—or that they’d rather avoid.
Despite concerns about safety and ethics, many are content
to continue fluoridation because of its purported benefit: that it
reduces tooth decay. The Centers for Disease Control and Prevention’s
Division of Oral Health, the main government body responsible for the
process, says it’s “safe and effective.”
You might think, then, that fluoridated water's efficacy
as a cavity preventer would be proven beyond a reasonable doubt. But new
research suggests that assumption is dramatically misguided; while
using fluoridated toothpaste has been proven to be good for oral health,
consuming fluoridated water may have no positive impact.
The Cochrane Collaboration,
a group of doctors and researchers known for their comprehensive
reviews—which are widely regarded as the gold standard of scientific
rigor in assessing effectiveness of public health policies—recently set
out to find out if fluoridation reduces cavities. They reviewed every
study done on fluoridation that they could find, and then winnowed down
the collection to only the most comprehensive, well-designed and
reliable papers. Then they analyzed these studies’ results, and
published their conclusion in a review earlier this month.
The review identified only three studies since 1975—of
sufficient quality to be included—that addressed the effectiveness of
fluoridation on tooth decay in the population at large. These papers
determined that fluoridation does not reduce cavities to a statistically
significant degree in permanent teeth, says study co-author Anne-Marie Glenny,
a health science researcher at Manchester University in the United
Kingdom. The authors found only seven other studies worthy of inclusion
dating prior to 1975.
The authors also found only two studies since 1975 that
looked at the effectiveness of reducing cavities in baby teeth, and
found fluoridation to have no statistically significant impact here,
either.
The scientists also found “insufficient evidence” that fluoridation reduces tooth decay in adults (children excluded).
“From the review, we’re unable to determine whether water
fluoridation has an impact on caries levels in adults,” Glenny says.
(“Tooth decay,” “cavities” and “caries” all mean the same thing: breakdown of enamel by mouth-dwelling microbes.)
“Frankly, this is pretty shocking,” says Thomas Zoeller, a scientist at UMass-Amherst uninvolved in the work. “This study does not support the use of fluoride in drinking water.” Trevor Sheldon
concurred. Sheldon is the dean of the Hull York Medical School in the
United Kingdom who led the advisory board that conducted a systematic review of water fluoridation
in 2000, that came to similar conclusions as the Cochrane review. The
lack of good evidence of effectiveness has shocked him. “I had assumed
because of everything I’d heard that water fluoridation reduces cavities
but I was completely amazed by the lack of evidence,” he says. “My
prior view was completely reversed."
“There’s really hardly any evidence” the practice works,
Sheldon adds. “And if anything there may be some evidence the other
way.” One 2001 study
covered in the Cochrane review of two neighboring British Columbia
communities found that when fluoridation was stopped in one city, cavity
prevalence actually went down slightly amongst schoolchildren, while
cavity rates in the fluoridated community remained stable.
Overall the review suggests that stopping fluoridation would be unlikely to increase the risk of tooth decay, says Kathleen Thiessen,
a senior scientist at the Oak Ridge Center for Risk Analysis, which
does human health risk assessments of environmental contaminants.
“The sad story is that very little has been done in recent
years to ensure that fluoridation is still needed [or] to ensure that
adverse effects do not happen,” says Dr. Philippe Grandjean, an environmental health researcher and physician at Harvard University.
The scientists also couldn’t find enough evidence to
support the oft-repeated notion that fluoridation reduces dental health
disparities among different socioeconomic groups, which the CDC and others use as a rationale for fluoridating water.
“The fact that there is insufficient information to
determine whether fluoridation reduces social inequalities in dental
health is troublesome given that this is often cited as a reason for
fluoridating water,” say Christine Till and Ashley Malin, researchers at Toronto’s York University.
Studies that attest to the effectiveness of fluoridation
were generally done before the widespread usage of fluoride-containing
dental products like rinses and toothpastes in the 1970s and later,
according to the recent Cochrane study. So while it may have once made
sense to add fluoride to water, it no longer appears to be necessary or
useful, Thiessen says.
It has also become clear in the last 15 years that fluoride primarily acts topically, according to the CDC.
It reacts with the surface of the tooth enamel, making it more
resistant to acids excreted by bacteria. Thus, there's no good reason to
swallow fluoride and subject every tissue of your body to it, Thiessen
says.
Another 2009 review by
the Cochrane group clearly shows that fluoride toothpaste prevents
cavities, serving as a useful counterpoint to fluoridation’s uncertain
benefits.
Across all nine studies included in the review looking at
caries reductions in children's permanent choppers, there was evidence
linking fluoridation to 26 percent decline in the prevalence of
decayed, missing or filled permanent teeth. But the researchers say they
have serious doubts about the validity of this number. They write: “We
have limited confidence in the size of this effect due to the high risk
of bias within the studies and the lack of contemporary evidence.” Six
of the nine studies were from before 1975, before fluoride toothpaste
was widely available.
The review also found fluoridation was associated with a
14 percent increase in the number of children without any cavities. But
more than two-thirds percent of the studies showing this took place more
than 40 years ago, and are not of high quality.
Nearly all these papers were flawed in significant ways.
For example, 70 percent of the cavity-reducing studies made no effort to
control for important confounding factors such as dietary sources of
fluoride other than tap water, diet in general (like how much sugar they
consumed) or ethnicity.
When it comes to fluoridation research, even the best studies are not high quality. Although this was already well-established, it doesn't seem to be well-known.
“I couldn’t believe the low quality of the research” on fluoridation, Sheldon says.
The data suggest that toothpaste, besides other
preventative measures like dental sealants, flossing and avoiding sugar,
are the real drivers in the decline of tooth decay in the past few
decades, Thiessen says. Indeed, cavity rates have declined by similar amounts in countries with and without fluoridation.
Meanwhile, dental health leaves much to be desired in
widely fluoridated America: About 60 percent of American teenagers have
had cavities, and 15 percent have untreated tooth decay.
One thing the review definitively concluded: Fluoridation causes fluorosis.
This condition occurs when fluoride interferes with the
cells that produce enamel, creating white flecks on the teeth. On
average, about 12 percent of people in fluoridated areas have fluorosis
bad enough that it qualifies as an “aesthetic concern,” according to the
review. According to Sheldon, that’s a “huge number.” A total of 40
percent of people in fluoridated areas have some level of fluorosis,
though the majority of these cases are likely unnoticeable to the
average person.
In a smaller percentage of cases, fluorosis can be severe
enough to cause structural damage, brown stains and mottling to the
tooth.
Sheldon says that if fluoridation were to be submitted
anew for approval today, “nobody would even think about it” due to the
shoddy evidence of effectiveness and obvious downside of fluorosis.
There is also a definite issue of inequality when it comes to fluorosis. Blacks and Mexican-Americans have higher rates of both moderate and severe forms of the condition. Blacks also have higher levels. As of 2004, 58 percent of African-Americans had fluorosis, compared to 36 percent of whites, and the condition is becoming more common.
The Cochrane review concerned itself only with oral
health. It didn’t address other health problems associated with
fluoride, which Grandjean says need to be researched.
Many of the Cochrane study’s conclusions conflict with
statements by the CDC, the American Dental Association and others that
maintain fluoridation is safe and effective. The ADA, for example, maintains on its website
that “thousands of studies” support fluoridation’s effectiveness—which
is directly contradicted by the Cochrane findings. The ADA didn’t
immediately respond to requests for comment.
The CDC remains undeterred. “Nothing in the Cochrane
review” reduces the government’s “confidence in water fluoridation as a
valuable tool to prevent tooth decay in children as well as adults,”
says Barbara Gooch, a dental researcher with CDC’s Division of Oral Health.
The CDC and others “are somehow suspending disbelief,”
Sheldon says. They are “all in the mindset that this is a really good
thing, and just not accepting that they might be wrong.” Sheldon and
others suggest pro-fluoridation beliefs are entrenched and will not
easily change, despite the poor data quality and lack of evidence from
the past 40 years.
Derek Richards, the editor of the journal Evidence-Based Dentistry
(published by the prestigious Nature group) concedes that “we haven’t
got any current evidence” that fluoridation reduces cavities, “so we
don’t know how much it’s reducing tooth decay at the moment,” he says.
“But I have no qualms about that.” Richards reasons that because
fluoridation may help reduce cavities in those who don’t use toothpaste
or take other preventative measures, including many in lower
socioeconomic groups, it’s likely still useful. He also argues that
there’s no conclusive evidence of harm from fluoridation (other than
fluorosis), so he doesn’t see a large downside.
But most scientists interviewed for this article don’t
necessarily think fluoridation’s uncertain benefits justify its
continuation without more stringent evidence, and argue for more
research into the matter.
“When you have a public health intervention that’s applied to
everybody, the burden of evidence to know that people are likely to
benefit and not to be harmed is much higher, since people can’t choose,”
Sheldon says. Everybody drinks water, after all, mostly from the tap.
“Public health bodies need to have the courage to look at this review,”
says Sheldon, “and be honest enough to say that this needs to be
reconsidered.”
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