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We cannot afford bad science

Doug's Blog

We cannot afford unsound science – on either side of the fluoridation debate.

OK – so I was going to let this latest paper by Waugh et al [1], on the amount of fluoride in tea drunk in Ireland, pass without comment. But I've had emails from around the world asking whether it provides us with any new information on the risks of fluoride to human health.

Since I've made no secret of the fact that I don't like bad science, no matter who produces it, I've had to tell my correspondents that, in my opinion, this latest addition to the anti-fluoride library does nothing to forward our knowledge about the risks of drinking tea.

The basic problem is the science itself. If there's something wrong with the way that things have been done in a research project, then any speculation as to the meaning of the results is entirely worthless. And there's a rather difficult problem with these authors' approach to measurement.

Heroically gathering 54 different varieties to make the home-brews appears to cover the field quite comprehensively. I have nothing against this form of 'kitchen sink science' – indeed, I've used it myself on a number of occasions when a Court required simple demonstrations of some basic evidential principles.

So at first sight, you'd be inclined to assume that measuring fluoride content in a bunch of brew-ups, prepared in the same way that we make our tea at home, would provide a reasonable approximation to what we actually drink. And, you'd be right - indeed, it should.

But if you think the results actually mean something, think again. It's not the making of these brews that is the problem, but the way that their fluoride content was measured.

Measurements are supposed to be reliable.

To measure fluoride the authors used a fluoride ion-specific electrode, dipped into their tea infusions. But there's a problem with tea. Many, if not all varieties, contain an infernally high concentration of aluminium. The ratio of aluminium to fluoride in dried tea leaves is of course very variable, in both green and - especially - 'black' tea, but seems to average around 6 or 8 to one for many varieties. [2] However, they can get much higher. In one study, more than 16,000mg (16 grammes) of aluminium per KG of dry brick tea was found.[3]

And unfortunately, high levels of aluminium interfere with the accuracy of measurements of fluoride made with an ion-selective electrode. So quite properly the authors decided to have the aluminium content of six of their brews (and one tap water sample) measured by an independent laboratory, using a different analytical technique (Inductively Coupled Plasma Atomic Emission Spectroscopy - ICP-AES).

And they found that all of their six tea infusions contained aluminium at greater than the concentration - around 2.5mg/l - known to render the fluoride ion-specific electrode measurements unreliable. In fact aluminium content of the six brews ranged from 2.9mg/l to 7.2mg/l, - well above that concentration of aluminium that renders the ion-specific electrode unreliable.

Despite this rather difficult problem, the authors of this new paper simply ploughed on regardless, telling us that the fluoride content of their brewed-up 54 tea brands – as measured by their ion-sensitive electrode – ranged from 1.6mg'l to 6.1mg/l, with a mean of 3.3mg/l.

And, they should have stopped right there. After all, if you don't know how accurate – or wrong – your measurements are, then how can you possibly justify discussing what they mean? They mean nothing, end of story!

So now you see the problem? If all of the six brews they tested had too much aluminium for the reading from the ion-sensitive electrode to be reliable, then how many of the rest of the 54 brands that they brewed up had too much aluminium as well? Several of them? Most of them? Indeed, all of them?

We don't know, and the authors did not bother (or else could not afford) to check. It is entirely possible that ALL of the readings they obtained are wrong – possibly too low - due to aluminium interference.

The problem of bioavailability

This is, unfortunately, not the end of this tale of woe. If you assume that the readings the authors obtained are actually too low, you might argue that the threat from drinking tea is actually worse than the authors have

tried to make out. If so, then you'd be misled by another of the authors' arguments - their rather surprising approach to the issue of the actual bioavailability of that fluoride, to the Irish tea drinker.

Just because fluoride is present in the brew, this does not mean that that fluoride is actually all in a form that can be absorbed into the blood stream, which is where it is of primary concern..

The only way to establish this is to measure the blood serum level for fluoride before and after drinking the tea. Or, if you'd be satisfied with a less precise proxy measurement, how much fluoride appears in the urine of the consumer. These measurements would show us how much of the fluoride was absorbed and got into the tea drinker's blood serum.

Unfortunately, the authors did not do this. So now, we don't know how much fluoride was really in the tea brews, nor do we know how biologically significant whatever was there really was to the tea drinker.

Do you take milk with your tea?

So, here's one simple question , and one which the authors themselves asked - does the behaviour of tea drinkers affect how much of that fluoride in their tea gets into their own blood? As they tell us, in the real world many people drink tea with milk. But they strangely seem to have decided that this has no significance to the bioavailability of the released fluoride from the teabag. They are wrong.

Their curious statement that "Tea is also generally consumed with milk in the RoI. However, Gulati et al. assessed the effect of adding milk to English style tea and reported that there is no difference between levels of fluoride with or without addition of milk" is simply not correct. Of course the amount of fluoride in the tea itself is not changed by adding milk - once it's there, it will stay there, though it may not necessarily be in the same chemical form..

But adding milk to a tea infusion has a profound effect on what happens to that fluoride whilst it is brewing ,and most especially after the tea is ingested. Ignoring other contradicting sources, Waugh et al select only Gulati et al's paper [4] to make their own peculiar case.

Schulman and Vallejo [5], for example, summarised the research on the effects of milk and food on fluoride absorption from the stomach, using sodium fluoride solutions and a fluoride ion-specific electrode, and measured blood fluoride levels up to 4 hours after dosing their patients. But they gave milk to their subjects 15 minutes before introducing the fluoride, which is of course entirely unlike adding milk to brewed tea itself.

They reported that around half of the fluoride was unavailable when provided with a meal, and confirmed Ekstrand and Ehrnebo's [6] findings that when taken with milk, the absorption of fluoride is substantially reduced, endorsing these authors' advice that "It is suggested that the decreased bioavailability produced by dairy products should be taken into account when establishing fluoride dosage regimens for prophylaxis of caries."

This is widely regarded as correct, and this conclusion is at the heart of the many warnings in information sheets for medical fluoride products, such a fluoride pills and drops prescribed by dentists, that these products should NOT be given within an hour of consuming milk.

This is because milk 'inactivates' the fluoride, and impedes its absorption in the stomach – a minor problem that seems to have escaped the idiots recommending giving children 'Dental Milk' – which. of course, contains added fluoride, prepared even days in advance!


So I have two critical problems with this publication. Firstly the methodology is completely compromised by the unreliability of the reliance on a fluoride ion-sensitive electrode when used in the presence of interfering (and in most cases in this study, unmeasured) concentrations of aluminium in the brews. The failure of the authors to use a more reliable method to carry out their measurements invalidates their data – ALL of their data.

Secondly, the study is further compromised by the failure of the authors to demonstrate how much of that fluoride in the tea ( which is,of course, actually not known) is bioavailable once the brew had been consumed, especially with added milk, and even more so during or after a meal. Any debate as to the medical implications of drinking tea, founded on such unreliable research, is entirely speculative and unjustified.


1. Waugh D.T,, Potter W,, Limeback H., and Godfrey M. (2016) Risk Assessment of Fluoride Intake from Tea in the Republic of Ireland and its Implications for Public Health and Water Fluoridation. Int. J. Environ. Res. Public Health 2016, 13, 259; doi:10.3390/ijerph13030259

2.Shu W.S. et al(2003)Fluoride and aluminium concentrations of tea plants and tea products from Sichan Province, PR, China

3. Matsumoto et al (1976) Localisation of aluminium in tea leaves. Plant Cell Physiol 17. 627-631

4. Gulati, P.; Singh, V.; Gupta, M.K.; Vaidya, V.; Dass, S.; Prakash, S. Studies on the leaching of fluoride in tea infusions. Sci. Total Environ. 1993, 138, 213–222.

5. Schulman E.R., and Vallejo M.(1990) Pedatric Dentisty (July/August 1990) 12(4) 237-240.

6. Ekstrand J , Ehrnebo M :(1979) Influence of milk products on fluoride availability in man. Eur J Clin Pharmacol.16::211-15


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