This week we dive into another scientific controversy: fluoridated drinking water. The Centers for Disease Control and Prevention (CDC) considers it one of the 10great public health achievements of the 20th century, and yet others decry it as an attempt by the government to poison us (a conspiracy theory mocked in the movie Dr. Strangelove). What’s the truth? A recent research paper from Sweden tries to get to the bottom of this.
The benefit of fluoridation is in its well-documented ability to strengthen tooth enamel and this prevent tooth decay and cavities — also the reason why fluoride is added to toothpaste. The downside is that in large enough concentrations fluoride can impair cognitive development or, in the extreme, be lethal. The question is really whether a dose that is large enough to improve dental health is small enough to avoid the negative effects.
Even when it isn’t added, fluoride often can be found naturally in groundwater where it is absorbed from bedrock, but the level varies from place to place depending upon local geology. The World Health Organization (WHO) recommends that fluoride levels in water be no higher than 1.5 mg per liter. Local water utilities can either filter out fluoride from drinking water if the natural level is too high or add it in to meet a certain desired level. Seattle Public Utilities fluoridates our drinking water to 0.7 mg per liter, the level recommended by the CDC and the U.S. Department of Health and Human Services.
Sweden does not fluoridate its drinking water, but it does have a range of naturally-occurring fluoride levels in groundwater that the local utilities leave undisturbed if they register under 1.5 mg per liter. The researchers in this week’s paper decided to use that variation as the basis for seeing if different levels of fluoride have an impact on cognitive ability or other effects, some of which may be indirect.
First, they confirmed what is already known: The presence of fluoride in drinking water correlates with better dental health in the community consuming that water.
Second, they found no statistically significant correlation between cognitive ability and the level of fluoride in the drinking water.
Third, they found a positive correlation between levels of fluoride and labor income in the community, i.e. communities with higher natural levels of fluoride in the drinking water were economically stronger. This doesn’t mean that fluoride makes you smarter or better at your job; rather, it probably confirms the already existing evidence that better childhood health leads to better lifetime outcomes. If you have healthier teeth as a kid, you’re likely to have better overall health, and you will benefit from that for the rest of your life — including in the job market where you will likely be more productive and make more money.
One of the beautiful things about this study is that it’s based entirely upon naturally-occurring fluoride levels in water. That means it doesn’t run afoul of the potential for bias in other studies that have looked at this issue, namely that the decision to artificially fluoridate a community’s drinking water may be influenced by other factors — such as levels of education, health awareness, and economic prosperity — that would skew any potential comparisons. In other words: It’s hard to tell the difference between a community that improves its health by deciding to fluoridate its water and a community that is already healthy and health-educated that therefore chooses to fluoridate its water. But when the fluoride is naturally occurring — no one made the decision to add it — its effects are easier to discern.
What this means for us: The research further confirms the CDC and WHO guidance that low levels of fluoride in drinking water is a valuable public-health intervention that improves dental health, and the level of fluoridation in Seattle’s drinking water is well within the safe range.
Kevin Schofield is a freelance writer and the founder of Seattle City Council Insight, a website providing independent news and analysis of the Seattle City Council and City Hall. He also co-hosts the “Seattle News, Views and Brews” podcast with Brian Callanan, and appears from time to time on Converge Media and KUOW’s Week in Review.
The featured image is attributed to James St. John under a Creative Commons 2.0 license.
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