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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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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Fluoridation: the hip fracture deception

Warning – this book is deceptive

One of the myths promoted by the anti-fluoride people is that fluoridation is bad for our bones. As with similar myths the evidence used to support the claims usually comes from studies of situations where people have high F intake, often from natural sources.

However, there are studies which anti-fluoridationists can quote which do relate to fluoridated water concentrations.  For example, this is one of the many claims made by Christopher Bryson in his book The Fluoride Deception. This book tends to be used as scripture by anti-fluoridationists today so I thought I would look a bit more deeply into his claim.

Such deeper looks can often show problems of confirmation bias or uncritical evaluation of the literature – it did in this case.

1992

Bryson based his claim solely on work by Joseph Lyon, in particular the paper Hip Fractures and Fluoridation in Utah’s Elderly Population by Christa Danielson; Joseph L. Lyon; Marlene Egger; and Gerald K. Goodenough (1992). However, he does claim  “subsequent studies have found similar associations between fluoride in water and bone fractures.”

Danielson et al. concluded:

“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, suggesting that low levels of fluoride may increase the risk of hip fracture in the elderly”

2000

Well, it doesn’t take much searching to find papers with contrary conclusions. For example Community water fluoridation, bone mineral density, and fractures: prospective study of effects in older women by
Kathy R Phipps, Eric S Orwoll, Jill D Mason, Jane A Cauley (2000).

They concluded:

“Long term exposure to fluoridated drinking water does not increase the risk of fracture.”

So different conclusions, but why? Well Phipps et al. allude to the causes of contradictory conclusions in their introduction.

“While the benefit of fluoridation in the prevention of dental caries has been overwhelmingly substanti­ated, the effect of fluoridation on bone mineral density and rates of fracture is inconsistent. Ecological studies that compare rates of fracture specific for age and sex between fluoridated and non­fluoridated communities have variously found that exposure to fluoridated water increases the risk of hip fracture, (here they refer to Danielson et al 1992) increases the risk of proximal humerus and distal forearm fracture, has no effect on fracture risk, and decreases the risk of hip fracture. Ecological studies, however, have a major design flaw—they are based on community level data and cannot control for confounding variables at the individual level.” (My emphasis).

In contrast:

“We determined, on an individual level, whether older women with long term exposure to fluoridated water had different bone mass and rates of fracture compared with women with no exposure.” (My emphasis).

And they concluded:

“This is the first prospective study with adequate power to examine the risk of specific fractures associated with fluoride on an individual rather than a community basis. Our results show that long term exposure to fluoridation may reduce the risk of fractures of the hip and vertebrae in older white women. Because the bur­den of osteoporosis is largely due to fractures of the hip, this finding may have enormous importance for public health. If fluoridation does reduce the risk of hip fracture it may be one of the most cost effective meth­ods for reducing the incidence of fractures related to osteoporosis. In addition, our results support the safety of fluoridation as a public health measure for the con­trol of dental caries.”

So, if we compare the results from the two studies we see that while Danielson et al (1992) reported an increase in the risk of hip fracture for women drinking fluoridated water, Phipps et al (2000) actually reported a decrease in the risk. The difference being that Phipps et al (2000) removed confounding factors such as  medical history, drugs and supplements, reproductive history, menopause, alcohol consumption, exercise, smoking, caffeine intake, height and weight.

Relative risk of hip fracture for women with fluoride exposure compared to women with no fluoride exposure

2013

While preparing this I noted a new paper on this subject just published – Näsman et al (2013) “Estimated Drinking Water Fluoride Exposure and Risk of Hip Fracture:A Cohort Study

The abstract reports:

“Estimated individual drinking water fluoride exposure was stratified into 4 categories: very low, < 0.3 mg/L; low, 0.3 to 0.69 mg/L; medium, 0.7 to 1.49 mg/L; and high, ≥ 1.5 mg/L. Overall, we found no association between chronic fluoride exposure and the occurrence of hip fracture. . . . fluoride exposure from drinking water does not seem to have any important effects on the risk of hip fracture, in the investigated exposure range.”

So extra support for the conclusion that fluoridation does not lead to increased risk of hip fracture.

Motivated cherry picking

I think this shows the danger of cherry picking studies to support a preconceived position. And of relying on individual sources, or ideologically motivated sources like  The Fluoride Deception, for information.

There is a large amount of research on fluoride which to the uninitiated must seem contradictory. Proper review of this literature requires skills in critical thinking, and background in the field. The sort of thing that activist groups, and local body councils, don’t have.

Of course, I have no special background in this area either – and I don’t pretend that my summary here is at all definitive. However, it does show how misinformation can easily be promoted, with an apparent respectability conferred by  scientific references, when motivated people cherry pick.

See also:

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New Zealanders for fluoridation Facebook page