Japan’s Tooth Decay Rates Fell for 40 Years — Without Water Fluoridation
This is the kind of data fluoride defenders have a hard time explaining away.
This article originally appeared on The Defender and was republished with permission.
Guest post by Brenda Baletti, Ph.D.
Japan has achieved dramatic long-term declines in childhood tooth decay — despite never implementing nationwide water fluoridation and only recently recommending fluoridated toothpaste, according to a new study in BMC Public Health. The findings challenge long-standing assumptions promoted by the CDC and the ADA that community water fluoridation explains large-scale reductions in tooth decay.
Japan has achieved dramatic long-term declines in childhood tooth decay — despite never implementing nationwide water fluoridation and only recently recommending fluoridated toothpaste, according to a new study in BMC Public Health.
The research, by Yoshihisa Yamashita, D.D.S, Ph.D., of Kyushu Dental University, describes Japan’s experience as a “natural social experiment” that could reshape how public health experts address preventing dental cavities at the population level.
Unlike many other high-income countries, Japan has historically limited fluoride exposure during childhood — which makes the country a “unique and underexplored case.”
Using decades of national dental survey data, the study found that average rates of tooth decay among Japanese 12-year-olds fell steadily over roughly 40 years.
Levels dropped from a peak national Decayed, Missing, and Filled Teeth (DMFT) index score of 4.75 in 1984 to just 0.53 in 2023 — “well below levels historically reported in populations exposed to systemic fluoride through community water fluoridation,” according to the study. DMFT is the standard international measure of decayed, missing and filled teeth.
“This trajectory unfolded in the absence of nationwide community water fluoridation,” the paper states. High-fluoride toothpaste was not widely available in Japan until 2017 and was not officially recommended for school-aged children until 2023, according to the study.
Dr. Griffin Cole, conference chairman of the International Academy of Oral Medicine and Toxicology, said the study’s method of using national dental records across an entire population, rather than measuring fluoride exposure among a small group, provided important evidence on oral health.
“By examining real-world outcomes, Yamashita’s analysis provides strong evidence of what we already know: Oral health can improve through nutrition, behavior and broader public health measures, rather than adding fluoride chemicals to our water supplies,” he said.
The findings are the latest to challenge long-standing assumptions promoted by organizations such as the Centers for Disease Control and Prevention (CDC) and the American Dental Association that systemic fluoride exposure through community water fluoridation explains large-scale reductions in tooth decay.
Decades-old study by U.S. researchers still used to justify fluoridation?
The study compared modern Japanese cavity rates with historic U.S. data collected by early fluoride researcher and dentist H. Trendley Dean in the 1930s and 1940s, and later consolidated by F.J. McClure.
Despite a small study size and issues with collection bias, Dean’s research formed the scientific foundation for North American fluoridation policies by showing lower cavity rates in four communities with naturally fluoridated water supplies.
But according to the new study, Japan’s current cavity rate is substantially lower than the minimum levels observed in Dean’s high-fluoride communities — even though Japan’s drinking water contains effectively no added fluoride.
Yamashita said it was also notable that Japan has only recently introduced high-fluoride toothpaste. Most toothpaste previously available contained less than 1,000 parts per million (ppm).
Popular children’s toothpaste brands in the U.S., including kids’ Crest and Colgate, contain about 1,100 ppm.
The paper argues that broader social and behavioral changes likely play a major role in reducing tooth decay.
The author suggested several possible contributing factors, including:
A long-term decline in sugar consumption and shifts in dietary habits.
Changes in childhood feeding and parenting practices, including reductions in prolonged bottle feeding.
Universal access to dental care through Japan’s national health insurance system.
Improved oral hygiene awareness and preventive behaviors as a result of greater healthcare access.
Fluoride ‘not a magic bullet for controlling tooth decay’
Japan’s per-capita sugar consumption has declined by more than 30% since the 1970s, according to national statistics cited in the paper.
However, the author noted that cavity rates continued falling even after sugar intake stabilized, suggesting that multiple factors likely worked together over time.
Dr. Hardy Limeback, professor emeritus in the Faculty of Dentistry at the University of Toronto, told The Defender that a 1996 Japanese study found even lower tooth decay rates in Japan during World War II, when sugar supplies were scarce and rationing took place.
“The effects of total fluoride did not seem to have much effect on the caries rates in Japan in the 20th century,” Limeback said. “In that country, increasing fluoride exposures by means other than fluoridation did not appear to be ‘one of the top 10 public health procedures of the 20th century,’ as claimed for fluoridation by the CDC in America.”
“Fluoride is not a magic bullet for controlling dental decay,” Limeback added. “Limiting sugar intake is.”
Countries should look beyond fluoride for dental health solutions
The study arrives amid renewed international discussion about fluoride safety.
A 2024 U.S. National Toxicology Program review examined possible links between fluoride exposure and lowered IQ in children. A recent Cochrane Review found water fluoridation has minimal effects on dental health.
Following a landmark 2024 judgment that found fluoride at current levels recommended for water fluoridation in the U.S. posed an “unreasonable risk” to children’s health, communities and states across the country stopped adding fluoride to their water.
The ruling also mandated that the U.S. Environmental Protection Agency (EPA) regulate it.
An appeals panel recently vacated that decision. But the EPA has since launched a new investigation into the safety of water fluoridation, as public concern has grown.
Yamashita argued for a “broader multicausal approach” to oral health policy.
“Substantial and sustained reductions in dental caries can be achieved through multicausal pathways,” the paper concludes, “even in the absence of universal water fluoridation.”
Yamashita said countries seeking to reduce tooth decay should consider not only fluoride-based strategies, but also policies addressing diet, early childhood environments, access to care and wider social determinants of health.
He also suggested that a bias toward fluoride has posed a barrier to understanding the multicausal approach that can improve dental health.
“This analysis highlights insights that have long remained unrecognized — not because the evidence was unavailable, but because prevailing frameworks shaped what researchers expected to see,” Yamashita wrote.
Related articles in the Defender
Breaking: New Cochrane Review Finds Water Fluoridation Has Minimal Effect on Dental Health
Breaking: Federal Court Strikes Down Landmark Fluoride Ruling on Technicality — ‘Not the Science’
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