Fluoride in Drinking Water: Is It Safe?

From a lecture series presented by The Great Courses

Fluoride is added to many municipal water supplies to combat tooth decay. But some studies have shown that fluoride in drinking water can be harmful for pregnant women and their unborn fetuses, potentially lowering the child’s IQ. We’ll take a closer look at these studies to determine whether this is the case.

Person holding a glass, filling up a glass with water in the sink in kitchen at home
The word “toxins,” when used in a medical context, refers specifically to poisonous substances that are produced by living cells or organisms.

What Are Toxins, Actually?

When we hear the word “toxins,” we often think of dangerous chemicals lurking in our food, water, and cosmetics. At least that’s what the media would have us believe.

However, that word, when used in a medical context, refers specifically to poisonous substances that are produced by living cells or organisms.

These, by their proper definition, are natural substances, produced by organisms as a result of natural selection, typically to defend themselves against other organisms.

That’s right, plants and mushrooms make their own toxins—in fact, their own pesticides and herbicides and antimicrobials and poisons, so they can better survive.

You’re probably familiar with the story of the discovery of penicillin by Alexander Fleming. The antibiotic, penicillin, was naturally made by a mold organism to protect itself from bacteria.

This is a transcript from the video series The Skeptic’s Guide to Health, Medicine, and the Media. Watch it now, on The Great Courses Plus.

A classic study from 1990 showed that the vast majority by weight of pesticides—the chemicals that kill pests—found in garden vegetables were made by the vegetables themselves, not sprayed on by farmers.

So what happens to all of these toxins? It turns out that our bodies are remarkably adept at handling them, or at least most of them.

We have livers and kidneys whose job it is to detoxify our blood, to process these chemicals into less-toxic forms, and then excrete them outside in waste. The physiology is truly remarkable.

None of this, by the way, has anything to do with what’s advertised as detoxing supplements or foods or special diets. That’s all quackery, and entirely unnecessary.

The fact that such products have become so popular is a testament to marketing genius. They’re nothing you need to spend any money on.

Learn more about how we share our world with toxins

Mounting Concerns over Fluoride in Water

Nevertheless, there are certainly toxic chemicals in our environment that are cause for concern and can have a hugely negative impact on human health. This is demonstrated by the Flint, Michigan, water crisis in which lead was discovered in the residents’ water supply.

Then there are other chemicals in our water supply which appear on the surface to be harmful but, upon closer inspection, are relatively benign.

Group from the big sedimentation drainages. Water settling, purification in the tank by biological organisms on water station
There are some chemicals in our water supply which appear on the surface to be harmful but, upon closer inspection, are relatively benign.

Fluoride is added to many municipal water supplies to combat tooth decay, and there is substantial—close to overwhelming—proof that it’s safe and effective.

But a study in Mexico raised some alarms in 2017. Headlines included this from Newsweek: “Children’s IQ Could Be Lowered by Mothers Drinking Tap Water While Pregnant,” or, even more alarming, from Reader’s Digest: “If You Drink This Type of Water During Pregnancy, Your Child’s IQ Could Suffer.”

CNN’s title more accurately reflected the study that was done. They said “Fluoride Exposure In-Utero Linked to Lower IQ in Kids, Study Says.”

Unfortunately, most of these fluoride headlines overstated what the study showed. To better understand that, we have to look at the study itself.

Causation or Correlation?

The study was done in Mexico, on a population quite different from ours, in a community where fluoride is not added to the water. It was an observational study, not an experimental study, that looked at a single measurement of urinary fluoride during pregnancy, and correlated that with measures of intelligence when the children were ages 6 to 12 years.

Doctors writing papers using clipboard.
Even in the highest doses, early fluoride exposure was not associated with lower IQ.

The findings are interesting, but this kind of study cannot show that it was the fluoride exposure that caused differences in intelligence. Maybe there were other, more important environmental differences, or differences in the mother’s diet, or other factors in different neighborhoods that affected both urinary fluoride concentrations and fetal development.

Observational studies like these aren’t meant to look at what causes what, just at what is associated with what. That’s a huge difference, and one that the editors of Reader’s Digest and Newsweek didn’t seem to appreciate.

Also, as the CNN article stated, a prospective study on fluoride and intelligence was done in New Zealand in 2015, in this case looking prospectively over 38 years at children receiving varying levels of fluoride in early childhood, and comparing that exposure to repeated IQ testing.

There was no association found. Even in the highest doses, early fluoride exposure was not associated with lower IQ. Context, again, is key—look for that in media accounts. Do stories put the new information into context with what’s already known?

Learn more about how to evaluate an article’s scientific evidence

Chemicals in Food and Water: The Bottom Line

It’s difficult to say with certainty that a chemical at a certain concentration in the environment is 100 percent harmless to everybody, all the time, no matter what the circumstances and other exposures might be.

What we do know is that humans have evolved to deal with almost all of the chemicals in our food and water. Some of these chemicals are there naturally, like the natural amount of fluoride in the water in Mexico; sometimes we add extra for health benefits, like the fluoride added to drinking water in the United States.

The vast majority of biologically active compounds found in foods are there naturally. They’re just components of the food itself.

But we also add other chemicals, sometimes natural or synthetic pesticides, for instance, or fertilizers used to make food easier or less expensive to grow. Modern agriculture and water treatment have provided us with food and water that’s cheap and abundant.

But we need to maintain our vigilance to make sure it stays safe. The media can do an important job here, serving as both a watchdog of consumer concerns, like in Flint, Michigan, and as a way for people to learn about new scientific knowledge.

But the forces driving the business of media news—increasing eyeballs and clicks and shares—does tend to favor news that overstates the issue at hand.

There’s a difference between capturing public attention to address genuine issues and using clickbait to scare people.

From the lecture series The Skeptic’s Guide to Health, Medicine, and the Media, taught by Professor Roy Benaroch, M.D.

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