Is fluoride an essential dietary mineral?

Source: Dietary Minerals, Wikipedia

Anti-fluoridation activists often assure us that fluorine (F) is not an essential element. But what does that mean? Literally I guess it means that there are no identified biological pathways essential to human life involving F. So anti-fluoridation activists often claim the only safe level of flourine in the human diet is zero!

But whether an element is essential or not is often unclear or undecided. Some sources claim about 16 elements seem to be essential to maintain life. Others claim over 20 elements are essential.

Fluorine is rather debatable, as the above Periodic Table of the elements suggests. The Wikipedia entry on Dietary Minerals does say, however:

“Fluorine (as Fluoride) is not generally considered an essential mineral element because humans do not require it for growth or to sustain life. However, if one considers the prevention of dental cavities an important criterion in determining essentiality, then fluoride might well be considered an essential trace element.”

So F may well be considered an essential trace element, or a beneficial element. By the way, we should not let the fact that F is known to have harmful effects when in excess lead us to deny its beneficial effects. Probably all essential or beneficial elements and trace elements do.

Essential and beneficial elements usually display a “beneficial window” of  intake. This can be shown by a U shaped  graph when we plot the incidence of negative effects against intake (see figure below).

Source:  Howd & Fan, 2007 –  Risk Assessment for Chemicals in Drinking Water page 202.

So we expect to see that sort of relationship with F intake if the element is essential, or even just beneficial. If there are no benefits from F we would expect only an increasing incidence of negative effects when the intake increases from zero. Of course we also see that for essential or beneficial elements if we restrict our data to only high levels of intake.

Does F have benefits besides dental ones?

Do the benefits of F extend more widely than the prevention of dental cavities? I have often thought they do because F has a clear effect on the structure and solubility of hydroxyapatites – an important and major componet of bones. A small amount  of substitution of F for OH in the hydroxyapatite structure can strengthen such minerals and lower their solubility. Bioapatites are a major component of our skeletons, and play a role in many of our organs. This chemical substitution may actually have positive effects on bone health, and the properties of other bioapatites. Of course excessive substitution, or differentiation into different chemical crystalline phases, may also have negative effects when there is excessive intake.

By the way, F is not the only elements that substitutes at trace levels in bioapatites. There are many more and they can each influence the properties of the bioapatite.

Another way of looking at this is that pure chemically defined compounds rarely exist in the real world. Other minor elements are often incorporated into the crystal structure, or be present in a closely associated crystal phase.  These “impurities” or substituted elements usually impart features to the natural material which are greater or lesser than, or perhaps not even seen, in the pure compound. These features can be important to the biological role of crystals in nature and life.

Because biological systems are always exposed to a whole range of chemical elements at varying concentrations there will be no such thing as zero F intake. Nobody’s body is “fluoride free.”

Beneficial effects of F on human bones?

I recently checked out a paper which shows beneficial effects  of F on human bones along the lines I have suggested.  The paper is Yiming Li et al., (2001): Effect of Long-Term Exposure to Fluoride in Drinking Water on Risks of Bone Fractures. The authors are a group of researchers from the US and China. You can download the PDF here and check out methodology and other details.

Here’s one of the figures from their paper summarising the relationship of overall bone fractures to F content of the water supply used.

Effectively, this displays the U-shaped curve mentioned for essential elements in Risk Assessment for Chemicals in Drinking Water.

Or, perhaps more importantly – statistically significant increases in numbers of bone fractures occur at both low levels of fluoride in drinking water (<0.3 ppm) and at high levels (>4 ppm).

The authors express it this way:

“The data appear to suggest that there may be a “beneficial window” of fluoride intake for bone health, because an increased risk of overall bone fractures was detected in both the populations with deficient and excessive fluoride in drinking water.”

Not surprisingly this window corresponds approximately to current New Zealand advice for oral health  – concentrations of fluoride in the water supply in the range 0.7 to 1.0 ppm are beneficial.

So perhaps we should consider F as an essential, or at least, beneficial trace element as Wikipedia suggests. And perhaps health authorities in New Zealand should include bone health, together with oral health, in their advice on fluoridation.

The quality of research studies is critical

Other groups have produced similar conclusions to that of Yiming Li et al. – particularly that the incidence of bone fractures are reduced by fluoride doses in the beneficial range of F intake. But, these sort of investigations are very complex so it’s possible to find other studies which don’t show this result, or show only the effects of high fluoride intake. This raises the question of the quality of such investigations and the need for readers and reviewers to be particularly informed about such issues.

Many of these sorts of studies produce results of questionable quality because they ignore the role of other factors besides F in the water supply. For example, in many developed countries, and many developing ones, dietary intake of fluoride also comes from toothpaste, mouthrinses and dietary supplements. The high mobility of modern populations also makes it difficult to relate clinical effects to simple factors in the current environment of the individuals. It’s no wonder that attempts to relate health effects to fluoride concentrations in the public water supply produces controversial findings.

Mind you, that’s a great gift to the unscrupulous cherry-picking, uncritical reviewer with an ideological or activist axe to grind. If you are selecting studies to support a preconceived viewpoint the influence of other factors is not important – you just choose what suits your argument and ignore the quality. But if you are trying to establish a reliable picture of what is actually happening, as we hope our health professionals and scientists are, it’s important to consider the quality, and reliability, of each study.

My impression is that this particular study is considered of high quality because it used populations with a defined history of fluoride exposure. The authors say:

“In contrast to the U.S. population, residents of rural China rarely change residences, and most have been using the same water supply throughout their life. Because of its unique environmental and cultural conditions, such as virtually no residential mobility and a relatively consistent lifestyle, rural China has been considered a perfect “living laboratory” for studying the relationship between various factors and diseases. The survey results of our study sites and data from individual subjects show that fluoride exposure in rural Chinese communities is still limited to water and diet.”

And in their methodology:

“The residency of each subject was determined by the following three measures: (1) objective assessment by checking the Family Registry Book, an official document issued by the government; (2) a subject survey questionnaire; and (3) confirmation by village officials who were familiar with the subject.”

This sort of reliability of information is just not available for modern populations in most countries, making these sort of studies unreliable.

The lesson here is that there must employ intelligent and expert consideration when reading or reviewing research in this sort of area. People consulting such studies and reviews should also be aware of the dangers. When public debates, like that over fluoridation, occur we need to be aware of the way activists may draw unreliable conclusions from the literature and promote those unreliable conclusions to the public.

As an aside – this study also considered possible effects of factors like gender, smoking and alcohol – not surprisingly bone fracture were higher for men, and for those consuming alcohol!

Conclusion

So, is fluoride an essential element? I don’t know and I am hardly the person to decide. But clearly it is possible to argue the case that it may be, or that it is at least a beneficial element, provided dietary intake is neither too low or too high. It’s a complex area – just beware of activists with an axe to grind and a simple picture to support their claims.

See also:
Fluoridation
Fluoridation – are we dumping toxic metals into our water supplies?
Tactics and common arguments of the anti-fluoridationists
Hamilton City Council reverses referendum fluoridation decision
Scientists, political activism and the scientific ethos

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