32 APRIL 2020
Americans now have fluoridated water.
Still more Americans get fluoride from
soft drinks, most of which are made with
fluoridated water. Some bottled water is
fluoridated too. In 2007, Grand Rap-
ids, celebrating its historic role, erected
a 33-foot-high powder-blue sculptural
monument to fluoridation.
The fluoride revolution was not
restricted to the United States. The Orga-
nization for Economic Cooperation
and Development regularly surveys the
progress of its 36 member nations. One
variable it tracked until recently was the
number of decayed, missing, or filled adult
teeth in 12-year-olds, a measure of over-
all dental health. The top graph on the
next page depicts the results—uniformly
positive— for six nations that have widely
adopted fluoridation.
Graphs like this help explain why the
Centers for Disease Control and Preven-
tion in 1999 called fluoridation one of the
top 10 public-health advances of the 20th
century. Curiously, they also help explain why fluorida-
tion is opposed by the surprisingly durable cohort of
activists who barraged me on social media. The bottom
graph on the next page, based on the same OECD sur-
veys, tracks the number of decayed, missing, or filled
adult teeth in 12-year-olds from countries that have
not embraced fluoridation in a significant way or at all.
The differences between the two graphs don’t leap
out at the viewer. Nonfluoridated nations such as
Belgium, Luxembourg, and Denmark actually have
better dental health by this measure than the United
States, one of the world’s fluoridation champions.
Finland, Germany, Japan, the Netherlands, Sweden,
and Switzer land tried fluoridation, abandoned it years
later—and saw no rise in tooth decay. What’s going on?
One of the lesser-known advantages of
government- run health-care systems, such as Brit-
ain’s National Health Service, is the fact that because
taxpayers are funding everything, the government
occasionally tries to determine whether the money is
being spent usefully. In 1999, the government asked
the NHS to “carry out an up-to-date expert scientific
review of fluoride and health.” A research team based
at the University of York evaluated every study of fluo-
ridation it could find—about 3,200 of them. The
team’s conclusion was, it said, “surprising.” Despite
the long fight over fluoridation, few of the thou-
sands of studies counted as “high-quality research.”
The implication was that Britain had been tinkering
with its water supply with little empirical support.
Trevor Sheldon, the head of the York review’s advisory
board, was blunt: “There’s really hardly any
evidence” that fluoridation works, he told
Newsweek. “And if anything there may be
some evidence the other way.” These find-
ings were respectfully ignored.
In 2015, the Cochrane organization
waded into the debate. Founded in 1993,
Cochrane is a London-based global net-
work of about 30,000 medical research-
ers in multiple countries that provides
systematic analyses of medical issues. The
goal is to produce pains taking, rigorous
assessments of what research has—and
hasn’t— established about a given subject.
Cochrane has a fiercely guarded reputa-
tion for impartiality and thoroughness. Its
verdicts have global impact. Which may
be why the pushback on its fluoridation
work was so strong.
To evaluate the efficacy of water fluori-
dation, the Cochrane researchers wanted
to select properly conducted scientific
research, discarding studies that were
badly designed (too few participants to
produce sound data, for example) or incompetently executed (for instance,
the researchers didn’t follow their own protocols). To evaluate the studies,
the team used two simple but strict criteria: They needed to have two large
groups of subjects, one with fluoride (the intervention group) and one with-
out (the control group), and each group had to be examined at least two
times. Moreover, the studies needed to be prospective (meaning the scien-
tists announced beforehand what they were looking for, then measured it)
as opposed to retrospective (meaning the scientists sifted through historical
data looking for patterns). Scrutinizing medical databases, the Cochrane team
found 4,677 fluoridation studies. All but 155 of them—20 that focused on
tooth decay, and 135 that focused on dental fluorosis—failed to meet the
two criteria. Worse, all of the tooth-decay studies and all but a handful of
the fluorosis studies were, in the jargon, “at high risk of bias”—for example,
variables such as age and income hadn’t been properly taken into account.
The Grand Rapids study is an example of these problems. Not only was
it cut short when the control city, Muskegon, started fluoridating its water,
but the experimenters had not established whether the two populations had
similar incomes or ethnic backgrounds. Nor did the researchers evaluate
people’s teeth blindly, by taking X-rays to be examined by technicians who
did not know which group a patient belonged to. Instead the study dentists
simply looked into patients’ mouths and subjectively reported what they
saw—a recipe for what is called “confirmation bias,” in which people tend
to interpret what they see in ways that reinforce their prior beliefs.
The Grand Rapids researchers cannot be much faulted for these lapses,
according to the Cochrane spokesperson Anne-Marie Glenny, a researcher
at the University of Manchester School of Dentistry. In the late ’40s and
early ’50s, the proper procedures for clinical trials were just being established.
Few scientists understood how small imbalances between the intervention
and control groups could compromise an entire trial. And the researchers
definitely cannot be blamed for the unhappy fact that their experiment—
indeed, all of the original fluoride research—occurred before the introduction
of Crest, the first fluoride toothpaste, in 1956. Today, given that almost all