Hip fractures in the elderly and fluoride – contradictory evidence

Room for cherry-picking to confirm a bias. Separate Swedish studies report that fluoride can either prevent or promote the risk of hip fracture in the elderly. Image credit: Are hip fracture patients treated quickly enough?

Anti-fluoride activists are promoting a recent study linking fluoride intake and bone fractures. No surprise there. But they are cherry-picking a single study to support their agenda and scientifically literate people should see the wider picture and not ignore other studies which, on the whole,  convey a different story. This issue illustrates problems with epidemiological studies producing variable results and shows why people should avoid cherry-picking and look at the full range of studies in a field.

Here I consider just two studies on fluoride intake and bone fracture which produced different conclusions. Both studies involved people from Sweden where the natural fluoride levels in drinking water vary across the country.

Drinking water fluoride may protect against hip fractures

First a study from 2013:

Näsman, P., Ekstrand, J., Granath, F., Ekbom, A., & Fored, C. M. (2013). Estimated drinking water fluoride exposure and risk of hip fracture: A cohort study. Journal of Dental Research, 92(11), 1029–1034.

The main findings are illustrated in the figure showing the calculated Hazard Ratios for people of different ages living in areas of Sweden with “very low” (less than 0.3 mg/L), “low” (0.3 – 0.69 mg/L), “medium” (0.7 -1.49 mg/L) or “High” (greater than 1.5 mg/L) fluoride levels in the drinking water. The Hazard Ratio in the figure below is a measure of the number of hip fractures at these levels compared with the number of hip fractures at “Very low” fluoride concentration. The bars represent the 95% confidence intervals. The Hazard Ratios for the “very low” group are 1.0 and Hazard Ratios statistically significantly different to 1 (no effect) are coloured red.

Considering all people there is no statistically significant increase in the number of hip fractures for any level of water fluoride concentration compared with the “very low” levels. The number of hip fractures experienced by people in the two lower age groups (less than 70 years and 70 – 80 years) was significantly lower at higher water fluoride concentrations than at the “very low” concentrations. The authors say:

this “suggests a protective effect of fluoride among the younger (age younger than 80 years): however, the majority of fractures occurred above the age of 80 years (median age at time of fracture, 82.0).”

So a study suggested that the fluoride in Swedish drinking water does not encourage bone fractures and may actually protect against them in the lower age groups.

Fluoride may encourage hip fractures

Now a study from 2021 – the one anti-fluoride activists are promoting (for obvious reasons):

Helte, E., Vargas, C. D., Kippler, M., Wolk, A., Michaëlsson, K., & Åkesson, A. (2021). Fluoride in Drinking Water , Diet , and Urine in Relation to Bone Mineral Density and Fracture Incidence in Postmenopausal Women. Environmental Health Perspectives, 129(April).

Unlike Näsman et al (2013) which used drinking water fluoride concentrations as a measure of fluoride exposure, Helte et al (2021) used urinary fluoride and estimated dietary fluoride intake as measures of fluoride exposure. The Hazard Ratios were calculated from the number of hip fractures in the Tertile 2 groups (0.88 – 1.30 mg/g urinary fluoride or 1.74 – 2.41 mg/day dietary fluoride intake) and Tertile 3 groups (1.30 – 116.51 mg/g urinary fluoride or 2.41 – 11.16 mg/day dietary fluoride intake) compared with hip fractures in the tertile 1 groups (0.14 – 0.88 mg/g urinary fluoride or 0.26 – 1.74 mg/day dietary fluoride intake).

Note: The urinary fluoride units of mg/g represent mg of urinary F/g urinary creatinine. Creatinine levels were used to correct the spot values for dilution.

The Hazard Ratios that statistically significantly different to 1 (no effect) are coloured red in the figure below.

A bit complicated I know, but what the figure shows is no statistically significant increase in hip fracture numbers for the tertile 2 groups compared with the lower F intake tertile one group. But a significant increase in fracture numbers for the tertile 3 groups except for the women exposed to constant water fluoride concentrations since 1982 in the dietary F group.

Hertle et al (2021) also considered other types of fracture. There were no statistically significant increases in fractures in the upper tertiles for either the “all fractures” or “major osteoporotic fractures” classes.

So, a bit of a mixed bag but this paper is currently being promoted by anti-fluoride activists as evidence of a harmful result from community water fluoridation (CWF).

Critically assessing the evidence for bone fractures

It is easy to see why supporters of CWF may cite Näsman et al (2013) as evidence for lack of harm and opponents may cite Helte et al (2021) as evidence of harm from CWF. But neither approach is really scientific. The methodological differences and choice of factors considered can easily explain variable results. One should critically and rationally assess both of these papers, together with the many other papers reporting similar studies, before coming to any conclusion.

On balance, the published studies probably support the findings of Näsman et al (2013) and not Helte et al (2021). In fact, a systematic review and meta-analysis published in 2015 concluded that chronic exposure to fluoride in drinking water was not associated with a significant increase in hip fracture risk. The citation for this review is:

Yin, X.-H., Huang, G.-L., Lin, D.-R., Wan, C.-C., Wang, Y.-D., Song, J.-K., & Xu, P. (2015). Exposure to Fluoride in Drinking Water and Hip Fracture Risk: A Meta-Analysis of Observational Studies. PLOS ONE, 10(5), e0126488. 

It’s worth reproducing one of the figures from that review because it illustrates how epidemiological studies may, individually, support a claim of harm but when considered as a whole these studies do not support the claim. The figure below shows the range of Hazard Ratios obtained by a number of studies.

The lesson here is to be very careful of claims made on the basis of single cherry-picked studies. Especially when those making the claim have a bias they wish to confirm. Every claim should be critically and rationally considered using all the available studies.

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Local anti-fluoride activists tell porkies yet again

FFNZ confuses lack of low fluoride studies on rats with human studies

Well, I suppose that’s not news. A bit surprising, though, because they are claiming the absence of research on fluoridation and IQ – which sort of conflicts with the previous attempts to actually condemn and misrepresent the actual research on fluoridation and IQ.

Fluoride Free NZ’s (FFNZ) face book page is claiming:

Would you be interested to know that no studies have been conducted on fluoridated water at 0.7ppm to determine whether there is IQ reduction? The National Toxicology Program are currently completing research to fill this gap. You would have thought that they would have done this in the 1950s before starting the fluoridation program wouldn’t you?

There have actually been three recent studies from three different countries which have specifically investigated the claim of an effect of fluoridation on IQ – and, unsurprisingly, all threes studies showed there was no effect.

Here are those studies:

New Zealand

Broadbent, J. M., Thomson, W. M., Ramrakha, S., Moffitt, T. E., Zeng, J., Foster Page, L. A., & Poulton, R. (2014). Community Water Fluoridation and Intelligence: Prospective Study in New Zealand. American Journal of Public Health, 105(1), 72–76.

In fact, anti-fluoride activists in the US, as well as New Zealand, have campaigned against this study. Their major criticism is that the study also included the effect of fluoride tablet use. They argue that this makes the unfluoridated control group useless because many participants will have consumed fluoride tablets. However, they ignore the fact that the statistical analysis corrected for this but still found no statistically significant difference in IQ of children and adults from fluoridated and unfluoridated areas.

Sweden

Other critics of the Broadbent et al. (2014) study have raised the issue of experimental power because of the numbers of people in the study. This could be a valid issue as it would determine the minimum effect size capable of being detected. Aggeborn & Öhman (2016) made that criticism of Broadbent et al., (2016) and all other fluoride-IQ studies. Their study is reported at:

Aggeborn L, Öhman M. (2016) The Effects of Fluoride in the Drinking Water. 2016.

Aggeborn & Öhman (2016) used much larger sample size than any of the other studies – over 81,000 observations compared with around 1000 or less for the commonly cited studies. It was also made on continually varying fluoride concentrations using the natural fluoride levels in Swedish drinking waters (the concentrations are similar to those in fluoridated communities), rather than the less effective approach of simply comparing two villages or fluoridated and unfluoridated regions. The confidence intervals were much smaller than those of other cited fluoride-IQ studies. This makes their conclusion that there was no effect of fluoride on cognitive measurements much more definitive. Incidentally, their study also indicated no effect of fluoride on the diagnosis of ADHD or muscular and skeleton diseases.

Canada

Another recent fluoridation-IQ study is that of Barbario (2016) made in Canada:

Barberio, AM. (2016). A Canadian Population-based Study of the Relationship between Fluoride Exposure and Indicators of Cognitive and Thyroid Functioning; Implications for Community Water Fluoridation. M. Sc. Thesis; Community Health Sciences, University of Calgary.

This study also had a large sample size – over 2,500 observations. This reported no statistically significant relationship of cognitive deficits to water fluoride.

Incidentally, Barberio (2016) also found there was no evidence of any relationship between fluoride exposure and thyroid functioning. That puts another pet claim of anti-fluoride campaigners to rest.

Animal studies

So much for NZFF’s claim that “no studies have been conducted on fluoridated water at 0.7ppm to determine whether there is IQ reduction.” But, just a minute, they are quoting the National Toxicology Program (NTP):

“No studies evaluated developmental exposure to fluoride at levels as low as 0.7 parts per million, the recommended level for community water fluoridation in the United States. Additional research is needed.”

But they omit the next sentence from the quote:

“NTP is conducting laboratory studies in rodents to fill data gaps identified in the systematic review of the animal studies.”

The NTP is discussing the research with animals, mainly rats, where effects of fluoride on the cognitive behaviour of the test animals have been reported but the fluoride concentrations are very high. And NTP’s assessment base on the review of the literature found only “a low to moderate level of evidence that the studies support adverse effects on learning and memory in animals exposed to fluoride in the diet or drinking water.” Hence the need for more research.

As part of the NTP’s research, which is currently underway, there are plans to extend studies to low fluoride concentrations more typical of that used in community water fluoridation.

The high concentrations used in animal studies is a major flaw in the anti-fluoride activist use of them to oppose community water fluoridation. For example, Mullinex et al (1995) (very commonly cited by anti-fluoride campaigners) fed test animals drinking water with up to 125 mg/L of fluoride (concentrations near 0.8 mg/L of fluoride are used in community water fluoridation).

While it is unlikely that the NTP research will find any significant effects of fluoride on the cognitive behaviour of rats at the low concentrations used in community water fluoridation the anti-fluoride campaigners have their fingers (and probably toes as well) crossed.

NTP will begin publishing the results of their new research next year (see Fluoride and IQ – another study coming up).

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Fluoridation not associated with hip fracture, heart attacks of osteosarcoma – new study

A new Swedish study confirms fluoride does not increase risks of hip fracture, myocardial infarction, or osteosarcoma.

Community water fluoridation appears to have no association with increased risk of hip fracture, myocardial infarction or osteosarcoma.

That’s the conclusion from a new Swedish study. And these conclusions agree with most findings from earlier studies.

Peggy Näsman describes this new study in her PhD thesis:

Näsman, P. (2016). Epidemiological studies of fluoride exposure and hip fracture , myocardial infarction and osteosarcoma.

She used Swedish nationwide population-based registers for her investigations.

Sweden does not use community water fluoridation but its drinking water contains fluoride at various levels, including optimum or even higher concentrations. So Swedish population data are ideal for looking at possible links between the level of fluoride intake and specific health effects.

Näsman found no association between fluoride exposure level and risk of hip fracture using a  cohort of 452,824 eligible people with an exposure to the same drinking water source from birth. The drinking water fluoride levels  ranged between <0.1 and 2.7 mg/L . Similarly, she found no association between fluoride level and the risk of osteoporotic (low-trauma) hip fracture.

However, stratified analyses suggested that fluoride exposure in people younger than 80 years of age was, in fact, associated with a decreased risk for hip fracture.

There was also no association between fluoride exposure level and risk of myocardial infarction using a cohort of 455,619 eligible people with an  exposure to the same drinking water source from birth.  The drinking water fluoride levels  ranged between <0.1 and 2.7 mg/L . There was also no association with fatal and non-fatal myocardial infarction.

Finally, Näsman found no association between drinking water fluoride exposure and risk of osteosarcoma using a case-control study consisting of 363 eligible osteosarcoma cases identified in the Swedish Cancer Register, and 1,815 control subjects randomly selected from the Total Population Register. Here the drinking water fluoride levels ranged between 0.03 and 2.75 mg/L.

Anti-fluoridation campaigners often cite cherry-picked studies based on unreliable work or small numbers of subjects to argue that community water fluoridation is harmful. They have specifically claimed fluoridation causes increased risks of hip fracture,myocardial infarction, and osteosarcoma. However, the bulk of the scientific literature does not support these claims and this study once again confirms that.

Näsman is publishing her findings in three scientific publications:

Näsman P, Ekstrand J, Granath F, Ekbom A, Fored CM. Estimated drinking water fluoride exposure and risk of hip fracture: a cohort study. J Dent Res. 2013 92(11):1029-34.

Näsman P, Granath F, Ekstrand J, Ekbom A, Sandborgh-Englund G, Fored CM. Natural fluoride in drinking water and myocardial infarction: a cohort study in Sweden. Science of the Total Environment. 2016 562:305-11.

Näsman P, Granath F, Ekstrand J, Ekbom A, Sandborgh Englund G, Naimi- Akbar A, Fored CM. Natural fluoride in drinking water and osteosarcoma: a case-control study in Sweden. [Submitted]

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