Diane and some other folks asked me for a run down on fluoride in drinking water, so here I am, several weeks later, and more incoherent than I’d prefer. Blame my fetus.
Some background info (mostly from Wikipedia, which has a good, albeit long, run down): Fluoride is added to many public drinking water supplies in the U.S. (72% of them) and elsewhere to help prevent tooth decay. Evidence suggests that fluoridated drinking water prevents up to 40% of cavities. Fluoride also naturally occurs in ground water (and the environment in general), often at concentrations higher than what is added to water for cavity prevention (in these areas, it … is not added to the drinking water, because it’s already there).
Fluoride is controversial for a few reasons. Some people claim that it is mass medication without individual consent, while others claim that because dental health issues disproportionately affect children and those of lower socioeconomic status, it would be unethical to withhold such simple and effective treatment. From a water treatment standpoint (I asked an engineering friend who designs water plants), the chemicals can be a bit nasty to work with (obviously at an occupational level, they are dealing with highly concentrated fluoride, while we get very diluted amounts coming out of the faucet). It’s also one of the more expensive aspects to engineer and implement when building a water treatment plant, and frustrating because of how little drinking water is actually imbibed, versus used in other ways*. From a toxicological standpoint, there are issues of variable, uncontrolled exposure: fluoride is in the water, and water intake varies quite a bit person to person.
But, people were curious mostly about whether it was a scary chemical or not, so let’s focus on that. Right up front: Not worth worrying about, but worse than aspartame [the safest chemical in the world].
Optimum concentrations of fluoride in drinking water for dental health are 0.5 – 1.0 mg/L. The WHO guideline says the maximum concentration in drinking water should be 1.5 mg/L. The maximum contaminant level (highest amount allowed from an EPA regulatory standpoint) is 4 mg/L. Let’s look at the possible and actual effects of chronic fluoride exposure, one by one (primary source):
Dental fluorosis is a cosmetic issue – greying of the teeth. It can occur in a small portion of the population at recommended fluoride levels. If your teeth are too grey for your liking, I suppose you could get an expensive filter. It’s plausible you’ll get some cavities, or that your personal biochemistry means you need less fluoride, or none of the above. Verdict: Not worth worrying about.
Skeletal fluorosis is THE serious effect of chronic overexposure. Typified by chronic joint pain, calcification of ligaments, deformity, muscular wasting, and neurological effects. This really does NOT occur in the U.S. It is endemic in certain parts of India and Asia, where fluoride levels often range up to 8 mg/L. Though many areas have concentrations comparable to those in the US (<4 mg/L), these areas also have rampant malnutrition, which exacerbates the effects of high(ish) fluoride. They also drink a lot of tea, which is naturally high in fluoride**. Verdict: not worth worrying about unless you move to Asia, or are that guy from that one movie, or drink several gallons of tea every day for your whole life.
Increased Bone Fractures might occur at upper limits of allowable concentrations. Data suggest a dose dependent increase in fractures, but it is not statistically significant. However, populations getting no fluoride also had elevated fracture rates – this effect where an adverse outcome is seen at low (0ish mg/L) and high (4 mg/L), but not moderate (1.0 mg/L), exposure levels is called hormesis, and it is totally cool. Typical for vitamins and essential nutrients – you see toxicity with too much, but also with too little. The sweet spot is called the “therapeutic range.” All of this fracture business doesn’t really matter until you are old, and then being a post-menopausal lady, or being inactive, or way too skinny, or taking corticosteroids for a long time are a much bigger deal than your drinking water. Verdict: I’d like some fluoride, but not too much, please. I’ll still drink all the diet coke, though.
Kidney stones might be related to overexposure. In epidemiological studies in India of populations getting 3.5 – 4.9 mg/L fluoride, those with obvious skeletal fluorosis were 4.6 times as likely to get kidney stones. But again, exacerbated/confounded by malnutrition, and they have bigger problems at that point. In studies of populations in developed countries getting 1.5 mg/L, there was no effect on rate of kidney stones, or actually lower rates. It is plausible mechanistically that folks who drink a lot of water (3 L/day) in areas with high fluoride (4 mg/L) could see increased kidney stone rates. If I were getting recurring kidney stones, I would personally look into local fluoridation levels (after taking a hard look at my diet, and also crying a lot, because ow). Verdict: don’t worry about it until like your third kidney stone.
Lower IQ might be an effect of chronic fluoride exposure. Only a few small, poorly described studies exist, all centered on comparisons of flouridated and non-flouridated villages in China. Villages with higher levels of fluoride (~2.5 mg/L) had about a 10 pt reduction in IQ of kids compared to those with low levels (~0.4 mg/L). There was a high prevalence of dental fluorosis in the kids with lower IQ scores. Verdict: This is actually kind of interesting, but I’d like to see a study done at U.S. levels (1.0 mg/L).
Alzheimer’s is unlikely to be related. There was a mechanistic study in rodents that suggested a plausible link, but data in humans has actually suggested that fluoridation may reduce the occurrence. Verdict: Not worth worrying about at all.
Cancer is NOT an effect of fluoride exposure through drinking water. In animal studies, there was a tiny (significant) increase in risk of osteosarcoma in rats fed 175 mg/L for two years (i.e, their whole lives). That’s… a really freaking high dose. Here, let’s do some math. A rat drinks 10-12 mL/100 g body weight/day. For a svelte rat (250 g), that amounts to 25 mL (0.025 L) water per day. So, 0.025 L/day * 175 mg/L = 4.375 mg fluoride per day. Normalize to body weight, that’s 17.5 mg/kg/day***. A 70 kg human with average water intake (1.05 L/day) at average fluoride levels (1 mg/L) gets 1.05 L/day * 1.0 mg/L / 70kg = 0.014 mg/kg/day. At upper allowable exposure (4 mg/L) and upper water intake (3 L/day), it bumps to 3 L/day * 4.0 mg/L / 70 kg = 0.17 mg/kg/day. These are not even comparable, at 100 – 1000 times lower. Human epidemiological studies support this – no increased cancer risk from fluoridated drinking water. Verdict: Ridiculous.
To sum up my opinions, based on all this, I was actually a little surprised at some of this. I remain supportive of water fluoridation because I think evidence supports it doing a hell of a lot more good than any potential harm – especially in poor populations that tend to have less consistent access to routine dental care. I do think that in some cases, for some people, getting a fluoride filter (not your standard Brita pitcher – this is more involved and more expensive) could be a good decision. But generally speaking, nope. Don’t worry about it.
*Average U.S. water use per person per day is 80 -100 gallons. If an average person drinks 1.05 L/day (0.277 gallons), that means only 0.35% of the water they use every day is for drinking. Even at the upper 95% of water intake (2.9L/day) it’s only about 1% of water. That’s a lot of wasted fluoridation.
**Brewed black tea generally contains 1 – 5 mg/L fluoride. This doesn’t include additional fluoride from water used to brew the tea.
***Compared to aspartame, fluoride is the devil. 12,000 mg/kg/day with no effect, versus a paltry 17.5 mg/kg/day and increased cancer risk! The choice is clear. Drink Diet Coke instead of tea if you don’t want cancer****. Take that, hippies!
****Tongue firmly in cheek. Also tea might have some chemopreventive effects, but whatever, Diet Coke 4 Life.