Fluoridation: The RCT We Still Haven't Run (But Should)

post by ChristianKl · 2025-01-11T21:02:47.483Z · LW · GW · 5 comments

Contents

  The IQ Elephant Continues to Loom Large
  Salt:
  The ROI is Sky-High - A True Win-Win-Win
None
5 comments

Empiric status: My own idea written up with the help of Gemini 2.0 Experimental in dialog.

We're still coasting on the fumes of 1940s data when it comes to water fluoridation. Back then, fluoride toothpaste was a novelty, fluoridated salt was uncommon, and water filters were practically science fiction, let alone ones that can selectively remineralize with or without fluoride.

We're navigating a multi-variable optimization problem blindfolded. We have fluoride inputs from water, toothpaste, and salt, all interacting in poorly understood ways, impacting both cavity rates and, more concerningly, cognitive development.

The IQ Elephant Continues to Loom Large

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. 

The technology is here. We can do this right. Modern water filters with remineralization cartridges are the key.

Here's the plan:

  1. Factorial Design: Multiple arms to test different combinations of:
    • Water Fluoride Levels:
      • 0 mg/L (placebo - remineralization without fluoride)
      • 0.35 mg/L (half of the current CDC recommendation, exploring potential lower thresholds)
      • 0.7 mg/L (current CDC recommendation)
    • Toothpaste:
      • Standard fluoridated toothpaste (provisioned, with standardized use instructions)
      • Non-fluoridated toothpaste (provisioned, with standardized use instructions)

    • Salt:

      • Fluoridated salt (provisioned)
      • Non-fluoridated salt (provisioned)

      This creates a 3x2x2 factorial design, allowing us to disentangle the effects of each source and their interactions, with a clear focus on the impact of fluoridated salt.

  2. Targeted Community Selection: Conduct the study in a community with known poor water quality. This offers multiple benefits:
    • Ethical Appeal: Providing free, high-quality water filters is a significant social good.
    • High Participation Rates: The offer of free water filtration will be very well-received.
    • Enhanced Compliance: Participants receiving a tangible benefit (clean water) are more likely to adhere to the study protocol, including consistent filter cartridge replacement.
  3. Randomized, double-blind (as much as possible) allocation of households within the selected community to each of the experimental arms.
  4. Longitudinal data collection: Track dental health (cavities, etc.) and, crucially, cognitive development (IQ scores, standardized tests, etc.) over several years.
  5. Aggressive confounder control: Detailed surveys on other fluoride intake (dietary sources, etc.), socioeconomic variables, etc. Biomarker analysis (e.g., urinary fluoride) would be ideal for verifying exposure levels and controlling for further confounders.

The ROI is Sky-High - A True Win-Win-Win

The potential return on investment for this RCT is immense. We're talking about a potential population-wide impact on cognitive function, and fine-tuning dental health benefits. The cost of this study is negligible compared to the potential societal costs.

Conclusion: The Time for Inaction is Over. Let's Do This Ethically, Effectively, and Rigorously.

We've relied on outdated assumptions about fluoridation for too long. The potential cognitive risks demand a rigorous, modern investigation. Let's use the technology we have, run the damn factorial RCT with provisioned salt, refined fluoride levels and finally get some high-quality data to inform policy. 

5 comments

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comment by gwern · 2025-01-11T22:32:37.057Z · LW(p) · GW(p)

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.

Replies from: simon
↑ comment by simon · 2025-01-11T22:48:40.769Z · LW(p) · GW(p)

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 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.

Replies from: gwern, quinces6l
↑ comment by gwern · 2025-01-12T03:44:38.090Z · LW(p) · GW(p)

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.)

↑ comment by quinces6l · 2025-01-11T23:11:48.103Z · LW(p) · GW(p)

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  

Replies from: ChristianKl
↑ comment by ChristianKl · 2025-01-12T02:26:48.355Z · LW(p) · GW(p)

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.