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Bits and Pieces 4: Is It Safe to Fluoridate Water?

Fluoride is toxic at high levels but has health benefits  at low levels. Fluoride  is added to water at concentrations less than 1 ppm as it  helps to prevent tooth decay by hardening tooth enamel.  Tooth decay can allow bacteria to enter the bloodstream where they cause heart disease and other infections.  There are places where fluoride occurs naturally in water at ten times the concentration used to fluoridate water and there have been no long term effects except fluorosis, a brown stain on children’s teeth.

Fluoride is chemically about like chloride ion in the body – except that at high concentrations it forms a precipitate with calcium and ties it up. That’s the reason it is toxic at high levels. Fluoride can be used at fairly high doses to treat osteoporosis as it will keep calcium from leaving bones.  At 0.5 to 1 ppm, the amount usually used to fluoridate water, there have been no serious side effects. At above 1.5 ppm, fluorosis, a brown stain on the teeth may form in a few % of the population. There are places where natural sources of fluoride are as high as 10ppm and fluorosis is the only health effect found. Fluoride is toxic at high levels with an  LD50 of  125 ppm in rats and it is assumed to be about the same in humans. For comparison, the dose rate for aspirin is about 5 ppm  and the  LD50 in rats is 200 ppm (1 ppm is 1 milligram per kilogram of body weight).

There are very few sources of fluoride in people’s diets except water or products where it is an additive. The source of the fluoride doesn’t really matter as most inorganic fluorides hydrolyze to form fluoride and bifluoride ion in water. Many toothpastes use stannous fluoride. Many countries add fluoride to salt or even to milk as tooth decay  is considered to be a much more serious health risk than fluoride exposure. The exposure from all sources should be kept below 1.0 pm so those who have fluoridate water or salt should not use other fluoridated products or toothpaste. If you are worried about fluoride in you water, there are water filters that remove it from drinking water and it is easy to avoid it from other sources.

Update, 3/14/2011: The U.S. Department of Health and Human Services is announcing a proposal to change the recommended fluoride level to 0.7 milligrams per liter of water. The standard since 1962 has been a range of 0.7 to 1.2 milligrams per liter. There was no health risk at the higher level, but fluorosis has been observed in kids teeth, particularly those who may get fluoride from other sources.

Update, 11/13/2012  Poor oral health, dental disease, and tooth pain can put kids at a serious disadvantage in school, according to a new Ostrow School of Dentistry of USC study. “The Impact of Oral Health on the Academic Performance of Disadvantaged Children,” appearing in the September 2012 issue of the American Journal of Public Health, found that  73 percent of disadvantaged kids in Los Angeles have dental caries, the disease responsible for cavities in teeth. Children who reported having recent tooth pain were four times more likely to have a low grade point average—below the median GPA of 2.8—when compared to children without oral pain. Poor oral health and dental problems also cause more absences from school for kids and more missed work for parents. Treating tooth decay is prohibitively expensive for some and tooth decay has been implicated in a number of later health problems, even heart disease.

Update, 04/11/ 2014: Some people are concerned, not about the toxicity of the fluoride, but of arsenic in the fluorosilic acid that is used to fluoridate most city water supplies. The fluorosilic acid from fertilizer manufacture, used to treat most water supplies, comes as a 20% solution and one source was analyzed to contain about 3.3 ppm of arsenic. By the time the solution is diluted to 1 ppm of fluoride, the concentration of arsenic is diluted to about 1 part per trillion. That is about 10,000 times less than the EPA standard for drinking water, which is 10 parts per billion (ppb) arsenic. It is difficult to see how that can be a health risk.

For perspective, some lakes near older coal-fired power plants have been found to have upward of 200 ppb of arsenic in the water. If I were concerned about arsenic in my city’s water supply, I would look at the concentration in the water from the lake, if that is the water source.

(C) 2010 J.C. Moore

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