字幕表 動画を再生する 英語字幕をプリント How do my teeth look? Pretty good? Okay great. Fluoride in the water might be helping that, but it might also be doing other things. Fluorine is the 13th most abundant element on the planet. It's in seawater, foods like fish, tea and gelatin contain it, and it's a naturally occurring substance in minerals -- that is to say, IT'S IN ALL THE ROCKS, because it's everywhere, fluorine is washed into the water supply during erosion. Fluoride is just fluorine with an extra electron, and when we see it in toothpaste, food or drinking water, it's actually sodium fluoride, or in our bodies it's calcium fluoride. In the 1940s, scientists found that people living near natural water sources with 1 part per million of fluoride had fewer cavities. So, they decided to add fluoride up to that concentration to reduce cavities for everyone. Unsurprisingly, controversy ensued. Today, two-thirds of Americans have fluoridated public water, but studies have thrown into question the benefit of water-borne fluoride compared to topical fluoride… or toothpaste with fluoride. A study of 23,000 skeletons from medieval archaeological sites found people who live near the coast and consumed fluoride-rich fish had fewer cavities. Another CDC study compared kids in the late-60s to kids from the early 90s, and found a 68 percent drop in cavities. Though this could be due to fluoride toothpaste, not fluoridation as communities without fluoridation also saw a decrease. In the right concentrations -- that is, point-8 to 1.2 parts per million -- fluoride reduces tooth enamel solubility during its formation, helping it solidify and form teeth that are more resistant to bacterial attack. After the enamel is formed, fluoride helps prevent bacteria from producing acid that causes tooth decay. Of course, higher concentrations of fluoride can cause pitting in teeth, decay, and major health problems. Anything over 1.5 ppm can cause tooth decay, and 3 to 6 ppm can cause skeletal problems. And though there are some Chinese studies correlating high fluoride with IQ problems, no US city is even close to the 4 ppm EPA limit. Whether it's cool to add fluoride to the water is still a political and social point of contention. From a healthcare perspective, if we want our teeth to last, we've gotta keep the enamel free of harmful bacterial deposits - which fluoride does. Enamel, the outermost layer of the tooth, is the toughest stuff the body can make, but it can't repair itself. It needs help. Whether it belongs in the drinking water is a complicated question, because for those of us who didn't grow up with municipal drinking water, like me, we HAD it in our well water because the EARTH put it there. Municipal sources get it as an odourless and tasteless byproduct of phosphate fertilizers that makes no perceptible change to the water, according to the World Health Organization. The WHO also recommends community water fluoridation as the "most effective public health measure for the prevention of dental decay." Countries and states seem to be on board with fluoridation until someone finds damning evidence they shouldn't be, which, in 70 years, no one has yet found. So, for the moment, water fluoridation is still a thing, but what do you think about it? Do you care?