33Thetoothpaste contains fluoride, and that most people brush their teeth, assess-
ing the impact of fluoridated water remains highly problematic.
“It’s a really difficult area to evaluate,” Glenny told me. “You can’t really
do the ideal experimental study,” because it is next to impossible to assemble
two large, similar groups of people, one of which is not drinking fluoridated
water or brushing their teeth. On top of that, “measuring the confounders—
sugar consumption, socio economic status, and so on—is really tricky.” How
much, I asked, of the improved dental health of the ’60s and ’70s was due to
water fluoridation? How much was due to the soaring popularity of fluoride
toothpaste and mouthwash? And how much was due to rising affluence,
which generally translates into more visits to the dentist? “I’m not sure you
can answer that question,” Glenny said.The Cochrane group reported its work carefully.
The evidence, it said, is poor and sparse, but what lit-
tle there is “indicates” that the fluoridation of water
reduces cavities in children. But, the group said, “these
results are based predominantly on old studies”—from
before 1975—“and may not be applicable today.” For
adults, there is “in sufficient evidence,” old or new, to
determine whether fluoridation is effective. The report
did not support or attack fluoridation; it only asked for
more research.
Nonetheless, it set off an uproar. A blog post on the
Cochrane website attracted so many vitriolic comments
from anti-fluoridation zealots that
the organization eventually removed
it. When a writer for Harvard Public
Health magazine used the Cochrane
report to ask “Is Fluoridated Drink-
ing Water Safe?,” the heads of the
American Dental Association, the
American Public Health Associa-
tion, the American Dental Educa-
tion Association, the American Asso-
ciation of Public Health Dentistry,
the American Association for Dental
Research, and the Harvard School of
Dental Medicine demanded that the
article be amended or taken down.
(The story included earlier versions
of the two charts on this page.)
Fluoride, Glenny told me, is “the
only topic that I’ve been involved
in that has created so much angst
and controversy.” The responses
also critiqued the Cochrane report
itself. The president of the Ameri-
can Dental Association said that it
was “shaped by its unusually narrow
inclusion criteria, excluding 97 per-
cent of the more than 4,000 relevant
studies that it identified.” In a joint
letter, the president of the Ameri-
can Dental Education Association
and the executive directors of the
American Dental Association and
the American Association for Den-
tal Research concurred, scoffing at
Cochrane’s “rigid inclusion criteria.”
But the inclusion criteria were not
“unusually narrow” or “rigid”—they
were based on those in a standard
textbook, now in its fourth edi-
tion. The implication of the dental
experts’ critique seemed to be that if
only statistical analysts would lower
their standards, everything would
look good.How much difference does water fluoridation make? It’s hard to tell whether improvement in dental health has
ADAPTED FROM been caused by adding fluoride to public water systems or by better dental hygiene.
HARVARD PUBLIC HEALTH
MAGAZINE
Tooth Decay in Countries
Without Fluoridated Water1 1 1 1 1 2 2 2 2Austria
Belgium
Czech Republic
Denmark
Finland
France
Germany
Greece
Hungary
Iceland
Italy
Japan
Luxembourg
Mexico
Netherlands
Norway
Portugal
Slovak Republic
Slovenia
Sweden
Switzerland8 7 6 5 4 3 2 1 0975 980 985 990 995 000 005 010 0147Australia
Chile
Ireland
New Zealand
United Kingdom(^6) United States
5 4 3 2 1 0
1975 1980 1985 1990 1995 2000 2005 2010 2014
Average decayed, missing, or filled adult teeth in 12-year-olds
Average decayed, missing, or filled adult teeth in 12-year-olds
Tooth Decay in Countries
With Fluoridated Water