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Dear Mark: Is Fluoride Safe?

Today’s question addresses a contentious topic in the health arena: fluoride. It’s in (most of) the tap water we use, (most of) the toothpastes with which we brush, and even (all of) the teas we drink. It represents a bloody stage upon which skeptics and the natural health folks battle it out. Many in the Primal community would like to avoid it (as they would any government-endorsed hydroadditive) if possible; if it’s not possible, they at least want to know just how bad the stuff really is and whether its intake can be mitigated. Should we use fluoride-free toothpaste? Should we install household filters? Argh. So many questions and so few definitive answers… and here’s yet another. Ah, life!

Dear Mark,

What’s your take on fluoride? To drink fluoridated water, or to filter it? To use fluoride-free, natural toothpaste, or is it one of the benefits of living in a modern world?

I can’t seem to find any conclusive evidence on the web as to whether it is good or bad, and while I asked my dentist, I would love a second opinion. (his waiting room was full of posters advocating a “low meat, low fat diet”…)



I’m probably going to take flak for this one, but so be it. I’m not particularly concerned with fluoride in the water. While I’d definitely prefer it weren’t added to almost every municipal water supply in the country, I think we have far bigger fish to fry when it comes to health. Avoiding blatantly poisonous foods like grains [7], sugar [8], and industrial seed oils [9] is the most important thing we can do, followed by getting adequate amounts of exercise [10], sleep [11], and sun [12] while reducing or mitigating stress [13]. Once you’ve got the chest freezer full of pastured animals [14], a good workout regimen [10] dialed in, a source of pastured eggs [15] you can rely on, the perfect sleeping position [16] entrained, and you’re waking up without an alarm clock [17] totally refreshed and energized, then you can think about installing an expensive reverse-osmosis filter for your entire house or importing Nepalese glacier water. Before that, I don’t think it’s worth the trouble.

But don’t take my word for it. Let’s look at the evidence. I’m going to focus on a recent report [18] on current EPA standards regarding fluoride by the National Research Council’s Board on Environmental Studies and Toxicology. Before you assume that these groups, being governmental bodies, are automatically suspect, note that the EPA requested the report and, in response to the NRC’s findings, has recently recommended a reduction [19] in the maximum allowed dose of fluoride to be present in drinking water. They also suggest an optimum dose to be added – 0.7 mg/L – down from the previous 0.7-1.2 mg/L range. Currently, the average fluoride content of fluoridated municipal water supplies is 0.8 mg/L.

There is strong evidence that fluoride does offer protection against dental caries, but “the more the better” is probably not true and most recent reviews of the evidence suggest that topical fluoride (as in toothpastes, gels, and foams) are more effective than systemic fluoride. The NRC report references [20] several literature reviews that conclude “the major anticaries benefit of fluoride is topical and not systemic,” and a more recent study finds that evidence for topical fluoridation is far stronger than for municipal water fluoridation (PDF [21]). In fact, fluoride is most effective in the “post-eruptive” period [22], or after teeth have begun to appear, rather than as a preventive measure. As for systemic fluoridation? 0.7 mg/L of drinking water seems to be the sweet spot where cavity protection peaks. In fact, some studies show that as fluoride concentration approaches 1.2 mg/L, cavity incidence increases (PDF [23]), right in line with the NRC’s recommendations and just under the average dosage in most water supplies.

Fluoride appears to become really problematic to humans in two scenarios: when intake is extremely high; and/or when intake of other important micronutrients and minerals is low and inadequate. The primary health issues ascribed to fluoride consumption are bone health and thyroid dysfunction, for which there is ample evidence – but that doesn’t mean the amounts we typically get from fluoridated water are sufficient to provoke them. As per usual, the dose makes the poison.

Opponents of fluoridation claim that fluoride makes for brittle bones, low bone density, and higher fracture rates. Proponents claim the opposite. The truth appears to be someplace in between. One study [24] looked at different populations in China with different levels of naturally-occurring fluoride in the water ranging from 0.25 mg/L to 7.97 mg/L. Fracture rates increased at both extremes, with the lowest rates coming in populations with water fluoridation at 1 mg/L and the highest rates coming at between 4 mg/L and 7.97 mg/L. So, ultra low levels weren’t protective, l0w-to-mid levels were, while mid-to-high levels were definitely not.

It seems that, unsurprisingly, how fluoride affects bone mineral density depends on factors beyond just the amount of fluoride you’re getting. Calcium matters, for one. Rats on a calcium-deficient diet [25] displayed impaired bone density and strength when given fluoride at 10 ppm and 45 ppm, while it took fluoride at 45 ppm to induce bone density problems in rats with sufficient calcium. Note that it only took sufficient calcium rather than supranormal amounts of it to protect bone density. Vitamin D matters, too; researchers induced rickets [26] in vitamin D [27] deficient rats by giving mega doses of fluoride (between 30 mg/L and 100 mg/L, unheard of doses that you’d never encounter in real life). Giving vitamin D prevented rickets, even though intestinal absorption of fluoride was increased with vitamin D supplementation. And it looks like magnesium interacts with fluoride, too. Magnesium deficient rats have more fluoride in their bones and teeth [28], and a magnesium deficiency increases fluoride absorption rates.

Iodine [29] status of the organism interacts with, and sometimes predicts, how fluoride will affect the organism. For example, rats with sufficient iodine intake are able to tolerate drinking water with a fluoride content of 10 mg/L without negatively affecting thyroid status. At 30 mg/L, those same rats display reduced thyroid function and increased thyroid weight [30]. If rats are iodine deficient, however, 10 mg/L of fluoride is enough to severely hamper thyroid function. Iodine deficient cows are also more vulnerable [31] to fluoride’s effects on the thyroid.

Since we can’t give megadoses of fluoride to iodine-deficient humans in RCTs, human studies are mostly epidemiological, and thus not conclusive. That doesn’t make them any less interesting, though. Workers in an aluminum processing plant showed signs of fluorosis [32] and thyroid dysfunction; fluoride is a common byproduct of aluminum plants, so aluminum workers are exposed to an inordinate amount of fluoride on a daily basis. 65% of workers with more than ten years of service at the plant and 54% of workers with stage 2 fluorosis had hypothyroidism, while 76% of the workers diagnosed with chronic fluoride intoxication (indicated by liver damage) also had hypothyroidism. In other words, the greater their exposure to fluoride, the greater their chances of developing hypothyroidism. The average intake for workers was 10 mg of fluoride per day. For comparison’s sake, most fluoridated tap water contains around 1 mg/L fluoride, so you’d have to drink 10 liters of tap water just to approach the amounts these workers were taking in. Another study actually tried to use fluoride as a treatment for hyperthyroidism. Out of fifteen patients with clinical hyperthyroidism, six responded well to fluoride treatment, with basal metabolic rate lowering to normal levels and the symptoms of hyperthyroidism abating. Although fluoride treatment was considered statistically ineffective in the other nine patients (most of whom had Grave’s disease [33], an autoimmune hyperthyroid disorder that isn’t really linked to iodine intake), some displayed modest signs of improvement nonetheless.

Overall, iodine status seems to determine whether fluoride will negatively affect the thyroid. Excessive amounts of fluoride exert negative effects regardless of iodine status, but standard fluoridation should be pretty harmless to the thyroid as long you get enough iodine.

They also looked at data on fluoride and various cancers [34], cognitive deficits, reproductive dysfunctions [35], liver/kidney/immune systems [36], but found nothing conclusive. Acutely elevated intakes beyond what you’d get from 4 mg/L exposure was linked with liver and kidney damage, but no evidence that normal intakes are dangerous. They also note that folks with renal impairments tend to accumulate and absorb more fluoride than people without kidney problems (since excess fluoride usually passes through the kidneys en route to the toilet). I recommend reading the linked sections, as they go over all the evidence and explain why it might mean something or why it might not. I’m not totally convinced we have nothing to worry about. There’s a lot to wade through, including some interesting cancer [37] epidemiology.

What about other sources of fluoride? Fluoride isn’t just in the water we drink. It’s also in the products that use tap water, like soda and beer. It’s in tea [38] leaves, with black [39] having the highest levels and white [40] having the lowest. Although one woman even developed severe skeletal fluorosis [41] from drinking two gallons of tea each day for thirty years, tea consumption has reams of epidemiological and clinical evidence for its benefits that can’t be thrown out simply because of the fluoride content. Moderation is key, and longer brewing times increase fluoride release. It’s also commonly found in toothpaste. A pea-sized dollop of fluoride toothpaste has about 0.3 mg fluoride [42], while a larger, commercial-esque serving contains upwards of 2.25 mg. Don’t swallow your toothpaste (whether you use fluoride-free or not) and you’ll be okay.

Bottom line? Fluoride is a ubiquitous trace element that you can’t completely avoid, so to lose sleep over it is probably counterproductive. To wage campaigns against it and spend your days raging about it probably cause more stress and harm than they help. It’s in the food, in the soil, in tea leaves, in the water, and in any product that uses or includes municipal water. The best advice is first to avoid processed food, which you already do (right?). Next, eat lots of plants and animals to insure mineral repletion (while avoiding grains [7] and legumes [43] rich in mineral-binding phytic acid). Then, get daily sun [44] or take a vitamin D supplement. Last, eating good Primal food [45] means you’re avoiding the processed junk and sugary drinks that are high in fluoride. After that, I think you’re good. If you’re anything like me, you’re probably getting most of your hydration through real food, rather than gallon jugs of bottled water [46] – so there’s another avenue of avoidance. To be on the safe side, check the local levels of fluoride (some naturally occurring water sources have levels far higher than the 0.7 mg/L-1.2 mg/L they add to water, so even non-fluoridated areas could be getting really high levels, which you do want to avoid) and respond accordingly. A reverse-osmosis filter, while expensive and somewhat wasteful, will remove fluoride.

It may be that I’ve been sheltered from water fluoridation – Malibu only recently got fluoride added to the water supply – but I haven’t noticed any ill effects, and I drink both tap and tea. High levels are harmful, but they aren’t common. One estimate [47] pegs average daily intake of fluoride for a teenager living in a fluoridated area at around 1.85 mg. For non-fluoridated teens, it’s 0.86 mg/day. For people living and eating Primally? I’d wager it’s even lower and safer than that. You gotta look at the big picture. Complete avoidance of fluoride in all forms is impossible (and unnatural – remember, fluoride occurs naturally in water), so just make sure you’re good in all other aspects of health and let the chips fall where they will.

Did I miss anything? Are normal physiological doses of fluoride as dangerous as some people say? Is it all worth stressing over? I’m totally open to being enlightened. Let’s get it going in the comments (and I know you guys got plenty of ’em!).