Fluoridation: The RCT We Still Haven't Run (But Should)
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6simon
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4quinces6l
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The potential neurotoxic effects of fluoride are no longer a fringe concern. National Toxicology Program (NTP) monograph is clear: "moderate confidence" that >1.5 mg/L fluoride in drinking water associates with lower IQ in children.
Their meta-analysis is, as usual for fluoride studies, based heavily on the well-known Chinese studies, and the correlate is much smaller in the low-risk-of-bias studies, also as usual. It doesn't add much. None of these studies are very good, and none use powerful designs like sibling comparisons or natural experiments. They can't be taken too seriously.
The claimed harms of fluoride on IQ are strongly ruled out by the population-registry study "The Effects of Fluoride in Drinking Water", Aggeborn & Öhman 2021, which was published after the cutoff in their literature review.
1We may thus rule out negative effects larger than
0.14 standard deviations in cognitive ability if fluoride is increased by
1 milligram/liter (the level often considered when artificially fluoridat-
ing the water).
That's a high level of hypothetical harm that they are ruling out (~2 IQ points?). I would take the dental harms many times over to avoid that much cognitive ability loss.
They really rule out much more than that: −0.14 is from their worst-case:
Looking at the estimates, they are very small and often not statistically-significantly different from zero. Sometimes the estimates are negative and sometimes positive, but they are always close to zero. If we take the largest negative point estimates (−0.0047, col. 1) and the largest standard error for that specification (0.0045), the 95% confidence interval would be −0.014 to 0.004. We may thus rule out negative effects larger than 0.14 standard deviations in cognitive ability if fluoride is increased by 1 milligram/liter (the level often considered when artificially fluoridating the water).
So that is not the realistic estimate, it is the worst-case after double-cherrypicking both the point estimate and the standard error to reverse p-hack a harm. The two most controlled estimates are actually both positive.
(Meanwhile, any claims of decreases, or that one should take the harms 'many times over', is undermined by the other parts like labor income benefiting from fluoridation. Perhaps one should take dental harms more seriously.)
isn't the fact fluoride in toothpaste and brushing twice daily common likely to make it so there wouldn't be any dental harm from non-fluridated water? I've not done a deep dive on fluoride but my rough thinking is (a) it's possible it has harm (b) most people use fluoride/xylitol in toothpaste so the benefits of fluoride in water supplies seems not only negligible but likely non-existent in this day and age
There are mechanisms where fluoride goes directly from the mouth onto the surface of the teeth. There are also mechanisms where fluoride goes from the bloodstream into teeth.
The fluoride that goes directly from the mouth to the surface of the teeth seems clearly good for caries prevention at low side effects.
When it comes to the fluoride that goes through the stomach and blood supply, it's unclear to me whether that provides a benefit for caries prevention when you already have sufficient fluoride through toothpaste in the mouth. The side effects also seem unclear to me.
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