Large Swedish study finds no effect of fluoride on IQ

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Fluoride levels in Swedish drinking water (mg/L). Variation between municipalities. Source: Aggeborn & Öhman (2016)

A significant new Swedish study shows fluoride in drinking water, at the concentrations used for community water fluoridation, has no effect on IQ or other measures of cognitive ability. Similarly, it has no effect on diagnosis or prescription of medicines for ADHD, depression, psychiatric illnesses, neurological illnesses or muscular or musculoskeletal diseases.

On the other hand, the study showed positive effects of fluoride on income and employment status – most probably because better dental health is beneficial in the labour market.

This work is reported in:

Aggeborn, L., & Öhman, M. (2016). The Effects of Fluoride In The Drinking Water.

The study covers most of the health effects that anti-fluoride campaigners complain about. It really should put all these complaints to rest as the quality of this new study is much better than anything the campaigners rely on for the following reasons:

  • It involved a much large sample. Over 700,000 individuals were involved. The numbers included in specific measurements varied but they were much greater than those used in the studies cited by anti-fluoride campaigners. For example, almost 82,000 were involved in the cognitive ability comparisons – compared with a few hundred at the most in the comparable studies cited by anti-fluoride campaigners.
  • Estimates of effects were much more precise (as expected with large numbers of subjects) than for previous studies. The effect of fluoride on cognitive ability was always close to zero and for practical purposes was zero.
  • Statistical analyses were based on continuously varying fluoride levels – a much better approach than the simple comparison of data for low and high fluoride villages used in the studies cited by anti-fluoride campaigners.

Sweden is an ideal country for studying effects of fluoride at these low concentrations. It does not have artificial water fluoridation but its drinking water contains naturally occurring fluoride. The fluoride concentration in drinking water depends on the geology of the region so different Swedish communities consume water with different fluoride concentrations.

This graphic from the paper shows the number of people drinking water with various concentrations of fluoride. Note – the steps are 0.1 mg/L and although concentrations above 2.0 mg/L occur they are relatively rare. Sweden makes no attempt to remove excess fluoride until the concentrations exceed 1.5 mg/L – the maximum recommended by the World Health Organisation. For comparison, the recommended optimum concentration in  New Zealand is 0.7 mg/L.

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Histogram of numbers people drinking water containing naturally occurring fluoride at different concentrations. Source: Aggeborn & Öhman (2016)

Effects of fluoride on dental health

The Swedish data showed positive effects of fluoride on oral health. For example, the share of dentists visits “decreased by approximately 6.6 percentage points if fluoride is increased by 1 mg/l. This should be considered as a large effect.” Tooth repairs are closely related to fluoride. “If fluoride would increase with 1 mg/l, the share of 20-year-olds that had a tooth repaired would be decreased approximately 3.4 percentage points considering the 2013 sample. Again, this effect is large, especially for this cohort.”

Cognitive ability

Relevant data was used from national education tests and psychological tests during the years of the Swedish military conscription. The statistical analysis produced estimates which were all very small and often not statistically significant. The estimates were sometimes negative and sometimes positive. For example, an estimate including covariates showed that “cognitive ability is increased by 0.045 Stanine points [equivalent to about 0.3 IQ points] if fluoride is increased by 1 mg/l (a large increase in fluoride). This should be considered as a zero-effect on cognitive ability.”

Other possible health effects

The authors considered the effects of fluoride on the prescription of medicines for ADHD, depression, and psychoses. They also looked at psychiatric and neurological diagnoses from outpatient and inpatient registers, as well as diagnoses of muscular and skeletal diseases. Anti-fluoride campaigners often claim fluoride has a harmful effect on these health problems.

The was no effect of fluoride on the possibilities of being prescribed any of these medicines.  For example “the probability of receiving ADHD medicines is decreased by 0.2 percentage points if fluoride is increased by 1 mg/l. In economic terms, this effect is a zero-effect.”

It was the same for all the diagnoses considered –  “The estimated effects are small and often statistically insignificant.”

According to the authors:

“In conclusion, we do not find that fluoride has any effects on these health outcomes. This further strengthens our argument that fluoride does not have any negative effects for levels below 1.5 mg/l on human capital development or health outcomes related to human capital development. It is also interesting that we do not find any effects on diagnoses for muscular and skeleton diseases, which has been a question also discussed in connection to fluoride.”

Annual income and employment status

The lack of any effect of fluoride on IQ and other psychological and non-psychological estimates suggest that fluoride would have no effect on long-term outcomes like income and employment status. However, the authors suggested that it could have a positive influence on these outcomes because of better dental health.

And this was the case. Estimates of the effect of fluoride on income were always positive and usually statistically significant. The authors estimated that “income increases by 4.2 percent if fluoride increases by 1 mg/l. This is not a negligible effect and the estimate should be considered as economically significant.”

Similarly for employment status. “If fluoride is increased by 1 mg/l, then the probability that the person is employed is increased by 2 percentage points. This result thus point in the same direction as the results for log income where both these results are significant in economic terms.”

Further analysis indicated “that when dental repairs increases by 1 percentage point, income decreases by 2 percent on the same aggregate level. This effect is clearly economically significant. This indicates that fluoride improves labor market outcomes through better dental health.”

Conclusions

This is an important study. It involved large numbers of people, estimated outcomes were far more precise than in previous studies, it used continuously varying concentrations of fluoride instead of simply comparing high fluoride and low fluoride villages, and it considered possible long-term outcomes like income and employment chances.

The advantages of this study compared with the generally poor quality studies cited by anti-fluoride campaigners should put to rest arguments used by those campaigners. In particular, it should make the current campaigns relying on to IQ and cognitive effects irrelevant.

The authors comment that their data shows there is no need to consider negative health effects on consideration of the cost-effectiveness of community water fluoridation. I wonder if, in fact, these results will encourage policy makers to consider the cost benefits of improved income and employment chances in future calculations of the cost-effectiveness of fluoridation programmes.

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6 responses to “Large Swedish study finds no effect of fluoride on IQ

  1. So now we have positive proof or the advantages of “natural Fluoride’
    Forget that all fluoride is ‘natural’ The antis will push the its not “artificial” fluoride, that was in the paper.
    So now we will see some stupid scaremongering about that
    Clutching a big handfull of straws again
    No doubt the lawyer will have some strange reason why they should disregard it

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  2. We now have the Swedes producing yet more evidence that changing fluoride levels in drinking water does not affect the IQ level of the population.

    Meanwhile, here in NZ, Canterbury demonstrates what can happen to the more impoverished portions of our population when fluoride is not present in the water supply… http://www.stuff.co.nz/national/health/87791926/why-are-our-tamariki-more-likely-to-get-rotten-teeth

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  3. Are the authors of this study really suggesting that employment levels and incomes go up BECAUSE of fluoridation ?

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  4. No, David, not at all. They do not have fluoridation in Sweden.

    However, the data shows that income levels and chances of employment actually increase with fluoride concentration in drinking water. They hypothesise that this is a result of improved dental health and that suggestion is supported by other data.

    These economic outcomes were investigated because of the idea that if fluoride causes a decrease in cognitive ability this would be reflected as lower incomes and poorer chances of employment.

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  5. Sorry, I meant to say “because of higher fluoride ingestion”

    I am only a little ways into the paper but I am laughing about their methods for mapping who got how much. If you thought Malin’s research was suspect, perhaps you should apply the same scrutiny to this one. They both seem to have the same main problems. The measurement of total individual intakes is not available and the measurement of outcomes is suspect. The good new is that Malin’s new research, which should have been done in the 50’s, is going to be done.

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  6. Interesting, though, that you didn’t say that.

    Malin and Till simply used the proportion of the state that was fluoridated. It did not look at individual levels at all. (Plus it ignored confounding factors which when considered showed the extent of fluoridation had absolutely no effect on prevalence of ADHD). Till’s new research may well suffer the same problems. I really must contact her to see if she is willing to discuss my analysis of the problems with her paper – now is the time to do this before he repeats her mistakes. Unfortunately the cost of publication in that journal is just too much for me.

    Agreed, total intakes are very rarely available for fluoride but it is well known that the levels of F in drinking water are a valid approximation because it is a major component of total intake. If that worries you then get onto Paul Connett and admonish him for relying on the poor quality Chinese studies which only consider village level – never individual intake.

    As for scrutiny of the Swedish paper – my assessment is that it is miles ahead of Malin and Till’s paper. The sample size is huge compared with previous studies. Covariates were considered – but as there was no effect of fluoride on the parameters considered the question of confounders really doesn’t come up.

    The other advantage is that, except for the dental health data, the measured parameters were for individuals.

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