There’s fluoride in my water?

Today, 64 percent of Americans will drink and bathe in fluoridated water.

Meanwhile Watsonville, CA is at the end of a decade-long debate and legal battle to keep fluoride out of their drinking water. The California Dental Association offered to pay for installation of fluoridation equipment to protect the community from dental decay. After a court case, the city was ordered to fluoridate the water or start paying a fine for each unfluoridated day. Soon the city will be installing a fluoridation system and adding fluoride to the drinking water. Watsonville has a determined opposition against fluoridating the water. As an intern at Santa Cruz Sentinel, I am researching the science and questions surrounding drinking water fluoridation. I will be a contributing reporter to a longer article on fluoridation in Wastonville in a few weeks.

photo by Marissa Fessenden

Most people against fluoridating water do not believe that it is a communist plot to keep the population docile. And I don’t mean to belittle their concerns. Stanley Kubrick’s movie is the first thing that many people think of when they aren’t aware of the discussion surrounding water fluoridation.

And if you haven’t seen Dr. Strangelove, get thee to a video rental place.

Anti-fluoridation activists cite some of the following concerns: Fluoride is not effective at reducing tooth decay. Fluoride causes health problems  (large doses are poisonous, true, but the evidence on whether it causes cancer is pretty slim). Fluoridating water is too expensive to justify. Fluoridating water is mass compulsory medication. Meanwhile, the CDC has community water fluoridation listed as one of the 10 Great Public Health Achievements in the 20^thcentury.

            Fluoridation of drinking water began in 1945 and in 1999 reaches an estimated 144 million persons in the United States. Fluoridation safely and inexpensively benefits both children and adults by effectively preventing tooth decay, regardless of socioeconomic status or access to care. Fluoridation has played an important role in the reductions in tooth decay (40%-70% in children) and of tooth loss in adults (40%-60%).

I don’t mean to pull my punches here. But I don’t want to spend time addressing these points here in this blog post. I will be addressing those concerns in the newspaper article, so stay tuned! For now, I’m interested in why a practice with more than 60 years of government backing and extensive published research papers is still hotly contested by a few people.

In this (now too long) post, I try to understand the challenges people have in wrapping their mind around water fluoridation. Science and uncertainty

Have you read a headline proclaiming that salt will kill you, only to read another headline a year later telling you that salt is fine, don’t even worry about it? This cognitive whiplash comes from the way science is reported. News cycles demand that each story have a ‘peg’, or a reason why we care and why we are reading about it now. In most news, that peg is that something happened—a fire, a robbery, or a politician announces she is running for office. Science news often focuses on the result of a published paper. But there is a big problem with that.

Science is an ongoing process. As more data are collected, the picture becomes clearer. Researchers can usually only say that the reason A happens is not because of B. This has plagued the discussion of global climate change. As this article in Nature explains, scientists and science writers are still struggling with how to communicate uncertainty.

Results are sometimes over-hyped. Because readers and editors want to know why we should care about some scientific paper. Witness the result: “Scientists discover a possible key to reversing baldness” Oh great! Everyone thinks. But what they actually discovered was a gene that gives a chemical signal that triggers hair growth. That might lead to treatments for baldness, but don’t get too excited.

The wealth of information on the web

Internet searches are like digging through a compost pile. Sure, there’s some good dirt in there, but there’s also squirming worms and rotting apples. For researching any topic, Internet searches turn up some good stuff … and some not so great stuff.

The wealth of knowledge on the internet (photo by Marissa Fessenden, mural on UCSC campus)

What are you supposed to ‘believe’ when the ADA and the FDA and all those official acronyms present a dry account that leaves you with more questions? While passionately anti-fluoride websites answer all of your questions and leave you outraged and motivated?

Emotional appeals sometimes seem more satisfying. These websites seem more personal. Comments from readers echo the punchy text. Information from a real, live human being might seem more believable. A person cares more about your health than an acronym does.

On the fluoride issue, there are a lot of studies but the quality not always good.

Looking for articles in peer-reviewed journals can help (use Google Scholar). Some of the studies are old. This 10-year old review of fluoride literature is one of the more recent reviews.

I think this is because research only happens if it is funded. Most dentists and researchers take fluoridation as a settled issue. It was approved 60 years ago, let’s move on. That’s too bad, because it is clear from the confusion that the public isn’t quite as sure as dentists.

BUT for most of us not working as researchers, those articles can be hidden behind a pay wall. That means you need to be part of an institution that subscribes to the journal, or pay out of pocket for an individual article. This is a major issue in science communication. Open access journals are increasingly coming online, but for now, discoveries are locked away from the public. Even when you can read the whole paper, jargon and dense technical language can get in the way of comprehending the science…

Reading those darned scientific papers

Ugh. Some research papers are really great. Many have really great research. A lot are very difficult to read. It takes practice.

For example, here is a paragraph from a Harvard study that claimed fluoride levels in drinking water are associated with cases of osteosarcoma, a cancer of the bone:

Reeves [34] reported that only 65% of fluoridated water systems routinely have target levels of fluoride maintained in the drinking water, which may result in our misclassifying up to 35% of the adjusted water systems, categorizing them in the highest group (100% of target or greater) when some truly belong in the middle group (30–99% of target). While non-differential misclassification of exposure results in bias towards the null for a dichotomous exposure (A not B), Birkett [35] has shown that with three levels of exposure, the estimated odds ratio for the highest exposure level is biased towards the null, but for the intermediate category the estimate can be biased in either direction. Hence, in our study the misclassification might mask an effect that increases with dose. There were some major problems with the paper. Especially since the journal published a letter to the editor urging caution in interpreting the study’s findings. But this paragraph alone had me confused, then frustrated, then banging my head on my desk.

What does it mean?

Here’s my attempt at untangling this: If you have two possible categories, high levels (A) and low levels (B), errors estimating whether one data point is A or B would tend to even out. If you sometimes made a mistake estimating in which category a point fell, some of the points on line A should be on line B and visa-versa. Then the lines would tend to look more like each other. The errors would make it so you couldn’t see a difference between the two lines. That’s what “biased towards the null” means.

But with three levels (A, B and C), errors might lower the highest line, but they could raise or lower middle line. So in this case, the effect might be more than shown, but can’t be less (top line comes down and bottom line goes up= less effect; top line down and bottom line down=more).

Here’s the figure they showed in the paper:

Fig.1

“Fig. 1 Odds ratios and 95% confidence intervals relative to fluoride levels less than 30% of target are shown for males (panel a) and for females (panel b). The dashed line shows the odds ratios for the intermediate exposure category (30–99% of target fluoride level) and the solid line shows the odds ratios for the high exposure category (100% of target or greater)”

I’m also not sure why the authors of the paper only plotted data points for the top third and middle third of the fluoride levels.

So that is just one example of a dense and confusing study. Reading through all of the studies on fluoridation is headache inducing.

And even some of the peer-reviewed literature isn’t that great. That 10-year old review says that most studies are moderate to low quality. They did not rank any of the studies as high quality.

The numbers game

Fluoride is a poison.

You’re not supposed to let your kids eat fluoridated toothpaste when they brush their teeth, and ingesting more than 4.7 grams of sodium fluorosilicate at a time can kill you. (Sodium fluorosilicate is one of the chemicals used to fluoridate water. The LD 50 (median lethal dose) orally in rats is 70mg/kg, corresponding to 4.76g for a 68kg/150-pound adult).

Now, that is a lot of fluoride to ingest.

This is just an issue of numbers. There are many substances that are safe to consume in limited quantities but will kill you if you eat too much. Keep that in mind when you read or hear of a study that shows cancer in rats. How much fluoride where those rats ingesting?

So, how do you decide who to trust?

The fact is, most studies, most researchers, and most dentists agree that low levels of fluoride in drinking water reduces the number of cavities without causing other health problems.

Research is still happening. The government is probably not out to get us, to control our minds with fluoride.

Last January, the US department of Health and Human Services Agency announced that they were changing the recommended fluoride level from 1.2 parts per million to 0.7 parts per million.

This change came because too much fluoride can cause white spots and streaks in teeth, a purely cosmetic condition called dental fluorosis. This issue is tricky, so I’m not surprised that some people are not convinced. And that is probably a sign of healthy human skepticism. We can’t just believe everything that we are told. We have to think things through and come up with our own interpretations.

One point that I find a little troublesome is that fluoridating water does seem like compulsory medication. But I’m all for vaccines, so maybe I’ll change my mind.

Examining the safety of our water is important. No arguing that. We are made of water and we need it.

This is another one of those issues that needs good science journalism.