Why this dental researcher became concerned that fluoridation can harm human bone.
As a professor, I was fortunate enough to receive years of government funding to analyse the proteins that were responsible for the formation of teeth. I became intrigued by how fluoride interfered with normal tooth development and caused dental fluorosis. Dental fluorosis can range from very mild, almost undetectable white streaking or flecking of the enamel, to a more moderate chalky white discolouration (often with orange permanent staining) to a more severe kind where the enamel seems to be very fragile and ‘flakes off’ the surface leaving behind stained, mottled enamel (a topic of a future blog).
It made sense to me that if too much fluoride ingestion can interfere with the mineralization of teeth, then it could interfere with the process that makes the mineral in bone; both tissues are mineralized with the same fluoride-containing mineral called fluorapatite.
It had been well documented in animals that too much fluorapatite in bone changes the bone’s physical properties making it more brittle and more susceptible to fracture. There had been some human epidemiological studies linking increased fluoride intake from drinking water to increased hip fractures but there were also studies that showed no effect. Clinical drug trials using massive daily doses of fluoride (25 to 50 mg per day) to treat osteoporosis were a disappointment. The side effects were horrendous. Also, researchers found that although large doses of fluoride made bone thicker the bone became more brittle and fractured more easily. The use of fluoride as a bone ‘strengthening’ agent was abandoned.
But fluoridation wasn’t supposed to affect anything except teeth!
Most fluoride ingestion comes from drinking fluoridated water. Fluoride accumulates in bone and the older you get the more ends up in your bones. The concern that fluoridation was weakening bones and increasing the risk for hip fractures in the elderly was heightened by the publication of studies such as this one from Utah.
“We found a small but significant increase in the risk of hip fracture in both men and women exposed to artificial fluoridation at 1 ppm (1 mg/L), suggesting that low levels of fluoride may increase the risk of hip fracture in the elderly.” (Danielson, C., Lyon, J.L., Egger, M., and Goodenough, G.K. 1992. Hip fractures and fluoridation in Utah’s elderly population. Journal of the American Medical Association. 1992, 268:746-748.)
Hip fractures are devastating for the elderly. Up to 36% of the elderly with hip fractures are dead within a year. http://www.ncbi.nlm.nih.gov/pubmed/19421703
If just one hip fracture is attributed to fluoridation, that’s one too many, in my mind. Almost 20 years ago I proposed that Canada consider reducing or eliminating fluoride from drinking water to reduce the risk of bone damage in Canadians (Limeback, H. Fluoride accumulation in human teeth and bones: Is dose adjustment now required? Canadian Journal of Public Health 1993, 84:78-81).
There was really no data in North America that looked at the quality of human bone exposed to low levels of fluoride (fluoridation). So, I decided to secure the help of a well-known bone researcher, Dr. Marc Grynpas of Mt. Sinai Hospital in Toronto, to apply for federal funding to study the effect of fluoride on human bone quality.
Our “Toronto-Montreal Bone Study”
The study, conducted primarily by a PhD student by the name of Debbie Chachra, was simple: she collected donated femoral heads (the tops of the leg bones) from patients at the Mt. Sinai Hospital in Toronto (a fluoridated city since 1964) undergoing total hip replacement, and examined the changes in anatomy and biomechanical properties, comparing the Toronto bones to donated bones from patients at the Montreal Jewish General Hospital (Montreal has never been fluoridated).
Here are some of the observations from that study (her thesis was published in 2001 but the peer-reviewed paper from that study did not appear until 2010) http://www.ncbi.nlm.nih.gov/pubmed/20858781
- Toronto bone samples contained significantly more fluoride than the Montreal bones (1033 ± 438 ppm vs 643 ± 220 ppm)
- fluoride accumulates with age (confirming other published studies)
- “the strength of the bone (was) lower for the more fluoridated group” [the ultimate compressive strength and yield to compressive stress declined with increasing fluoride (p < 0.05)]
- variability of results made it difficult to be certain of the fluoride effect (Debbie managed to secure a total of 92 femoral heads in total; it would have been nice to have collected a lot more specimens)
I suspect if this study were to be repeated with a greater number of patients, with a more homogenous group and limited to only the elderly who have been ingesting fluoridated drinking water for 60 or more years, the results would have been striking.
The York Review: Limitations of Ecological Studies
A group of epidemiologists in the UK, after systematically reviewing the quality of the various epidemiological studies, reported in the ‘York Review’ that fluoridation was not associated with an increased risk of bone fracture. http://www.york.ac.uk/inst/crd/CRD_Reports/crdreport18.pdf
Quite often, the York Review is quoted as the final word that fluoridation does not result in increased bone fractures. Can one really say that? The York reviewers used the meta-analysis technique, which is a systematic and statistical analysis of several studies combined. For an explanation see http://www.medicine.ox.ac.uk/bandolier/painres/download/whatis/meta-an.pdf
However, ecological studies have a huge potential for bias and errors (called ecological fallacy) http://www.nap.edu/openbook.php?record_id=11571&page=439
Using the GIGO principle (“garbage in, garbage out”) I’m not convinced the York reviewers proved much at all regarding the safety of fluoridation and bone quality. Inferences can be made about individuals from the ecological studies at the population level but so many variables still have to be accounted for that we really should be funding properly conducted clinical trials using outcome measures such as serum, urine and bone fluoride levels, bone biomechanics and bone histology.
What about people who retain more fluoride?
Susceptible subgroups of the population retain more fluoride because…
- they either drink a lot more water (diabetes, construction workers in hot climates, athletes),
- consume more fluoride on a dose/kg basis because they are smaller (infants and toddlers) or
- because they are unable to excrete fluoride properly (the elderly, people with renal failure).
With respect to renal patients, Dr. Grynpas’ group found in a study of 153 iliac crest bone biopsies taken from patient with renal osteodystorphy (ROD), a pathological change in bone, the following:
“These results suggested that in ROD, bone fluoride may diminish bone microhardness by interfering with mineralization.” (Ng AH, Hercz G, Kandel R, Grynpas MD. Association between fluoride, magnesium, aluminum and bone quality in renal osteodystrophy. Bone 2004, 34(1):216-24.)
I served on the US National Academies of Sciences Committee on Fluoride in Drinking Water (National Research Council). Our findings, Fluoride in Drinking Water: A Scientific Review of EPA’s Standards, were published in March of 2006 and can be found here: http://www.nap.edu/catalog.php?record_id=11571
We recommended that more research is needed on bone concentrations of fluoride in people with altered renal function, as well as other potentially sensitive populations (e.g., the elderly, postmenopausal women, people with altered acid-balance) to better understand the risks of musculoskeletal effects in these populations.
Fluoridation wasn’t supposed to affect the bones of our kids.
Our NRC committee concluded…
“Dose-response (biological gradient): For the most part, the observational studies discussed above observed higher fracture risk with higher exposure compared with 1 mg/L. The combined findings of Kurttio et al. (1999), Alarcón-Herrera et al. (2001), and Li et al. (2001) lend support to gradients of exposure and fracture risk between 1 and 4 mg/L.”
Dr. Steven Levy, a public health dentist, and his coworkers, started to look at bone health in a cohort of families they have been following in Iowa for many years.
In their 2009 publication looking at whether small daily fluoride exposures can affect kids’ bones they admit, “comparing results for girls and boys, we found consistently small positive associations of fluoride with bone outcomes for boys, but more commonly slight negative associations for girls.” (Levy SM, Eichenberger-Gilmore J, Warren JJ, Letuchy E, Broffitt B, Marshall TA, Burns T, Willing M, Janz K and Torner JC. Associations of fluoride intake with children’s bone measures at age 11. Community Dentistry and Oral Epidemiology 2009, 37: 416–426.)
Public Health’s continuing denial that our bones are at risk.
On Feb.17, 2011, the Association of Local Public Health Agencies (alPHa), in a press release, had this to say.
TORONTO — “The use of fluoride in drinking water is a safe, effective, and economical way to help prevent dental cavities with no scientifically proven adverse health impacts, according to Ontario public health agencies who voted overwhelmingly in support of the fluoridation of community drinking water at an Association of Local Public Health Agencies (alPHa) conference in Toronto last week.”
The use of fluoride in drinking water is safe? …with no scientifically proven adverse health impacts?… really?
Valid studies that show changes to the skeleton as a result of fluoridation have been published. More continue to accumulate in the literature. Public health must be unaware they exist or they interpret them completely differently. I suspect they give them no credence at all because these studies seem to contradict the “safe and effective” message.
Challenge to the reader: Ask your local public health representatives to provide the studies THEY have to prove that ‘the use of fluoride in drinking water is a safe, effective and economical way to prevent dental cavities’. Ask them why they are not monitoring fluoride levels even though municipalities insist on medicating their residents with the drug fluoride (to treat dental decay). Ask your doctor to have your fluoride levels checked.
Take home message for the reader: There ARE studies that show that fluoridation can have adverse health effects on bone.